Retargeting Changes for Migration from .NET Framework 4.0 to 4.7

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Introduction

Retargeting changes affect apps that are recompiled to target a different .NET Framework. They include:

  • Changes in the design-time environment. For example, build tools may emit warnings when previously they did not.

  • Changes in the runtime environment. These affect only apps that specifically target the retargeted .NET Framework. Apps that target previous versions of the .NET Framework behave as they did when running under those versions.

In the topics that describe retargeting changes, we have classified individual items by their expected impact, as follows:

Major
This is a significant change that affects a large number of apps or that requires substantial modification of code.

Minor
This is a change that affects a small number of apps or that requires minor modification of code.

Edge case
This is a change that affects apps under very specific scenarios that are not common.

Transparent
This is a change that has no noticeable effect on the app’s developer or user. The app should not require modification because of this change.

If you are migrating from the .NET Framework 4.0 to 4.7, review the following topics for application compatibility issues that may affect your app:

ADO.NET

DbParameter.Precision and DbParameter.Scale are now public virtual members

Details Precision and Scale are implemented as public virtual properties. They replace the corresponding explicit interface implementations, IDbDataParameter.Precision and IDbDataParameter.Scale.
Suggestion When re-building an ADO.NET database provider, these differences will require the ‘override’ keyword to be applied to the Precision and Scale properties. This is only needed when re-building the components; existing binaries will continue to work.
Scope Minor
Version ۴٫۵٫۱
Type Retargeting
Affected APIs

ASP.NET

HtmlTextWriter does not render <br/> element correctly

MachineKey.Encode and MachineKey.Decode methods are now obsolete

Multi-line ASP.Net TextBox spacing changed when using AntiXSSEncoder

Details In .NET Framework 4.0, extra lines were inserted between lines of a multi-line text box on postback, if using the AntiXssEncoder. In .NET Framework 4.5, those extra line breaks are not included, but only if the web app is targeting .NET 4.5
Suggestion Be aware that 4.0 web apps retargeted to .NET 4.5 may have multi-line text boxes improved to no longer insert extra line breaks. If this is not desirable, the app can have the old behavior when running on .NET Framework 4.5 by targeting the .NET Framework 4.0.
Scope Minor
Version ۴٫۵
Type Retargeting

Throttle concurrent requests per session

Details In the .NET Framework 4.6.2 and earlier, ASP.NET executes requests with the same Sessionid sequentially, and ASP.NET always issues the Sessionid through cookies by default. If a page takes a long time to respond, it will significantly degrade server performance just by pressing F5 on the browser. In the fix, we added a counter to track the queued requests and terminate the requests when they exceed a specified limit. The default value is 50. If the limit is reached, a warning will be logged in the event log, and an HTTP 500 response may be recorded in the IIS log.
Suggestion To restore the old behavior, you can add the following setting to your web.config file to opt out of the new behavior.

<appSettings>
<add key="aspnet:RequestQueueLimitPerSession" value="2147483647"/>
</appSettings>
Scope Edge
Version ۴٫۷
Type Retargeting

WebUtility.HtmlEncode and WebUtility.HtmlDecode round-trip BMP correctly

Details For applications that target the .NET Framework 4.5, characters that are outside the Basic Multilingual Plane (BMP) round-trip correctly when they are passed to the HtmlDecode(String) methods.
Suggestion This change should have no effect on current applications, but to restore the original behavior, set the targetFramework attribute of the <httpRuntime> element to a string other than “4.5”. You can also set the unicodeEncodingConformance and unicodeDecodingConformance attributes of the <webUtility> configuration element to control this behavior independently of the targeted version of the .NET Framework.
Scope Edge
Version ۴٫۵
Type Retargeting
Affected APIs

ClickOnce

ClickOnce supports SHA-256 on 4.0-targeted apps

Details Previously, a ClickOnce app with a certificate signed with SHA-256 would require .NET 4.5 or later to be present, even if the app targeted 4.0. Now, 4.0-targeted ClickOnce apps can run on 4.0, even if signed with SHA-256.
Suggestion This change removes that dependency and allows SHA-256 certificates to be used to sign ClickOnce apps that target .NET Framework 4 and earlier versions.
Scope Minor
Version ۴٫۶
Type Retargeting

Core

AesCryptoServiceProvider decryptor provides a reusable transform

Details Starting with apps that target the .NET Framework 4.6.2, the AesCryptoServiceProvider decryptor provides a reusable transform. After a call to TransformFinalBlock(Byte[], Int32, Int32), the transform is reinitialized and can be reused. For apps that target earlier versions of the .NET Framework, attempting to reuse the decryptor by calling TransformBlock(Byte[], Int32, Int32, Byte[], Int32) after a call to TransformFinalBlock(Byte[], Int32, Int32) throws a CryptographicException or produces corrupted data.
Suggestion The impact of this change should be minimal, since this is the expected behavior.Applications that depend on the previous behavior can opt out of it using it by adding the following configuration setting to the <runtime> section of the application’s configuration file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.Security.Cryptography.AesCryptoServiceProvider.DontCorrectlyResetDecryptor=true"/>
</runtime>

In addition, applications that target a previous version of the .NET Framework but are running under a version of the .NET Framework starting with .NET Framework 4.6.2 can opt in to it by adding the following configuration setting to the <runtime> section of the application’s configuration file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.Security.Cryptography.AesCryptoServiceProvider.DontCorrectlyResetDecryptor=false"/>
</runtime>
Scope Minor
Version ۴٫۶٫۲
Type Retargeting
Affected APIs

Calls to ClaimsIdentity constructors

Details Starting with the .NET Framework 4.6.2, there is a change in how ClaimsIdentity constructors with an IIdentity parameter set the Actor property. If the IIdentity argument is a ClaimsIdentity object, and the Actor property of that ClaimsIdentity object is not null, the Actor property is attached by using the Clone() method. In the Framework 4.6.1 and earlier versions, the Actor property is attached as an existing reference.Because of this change, starting with the .NET Framework 4.6.2, the Actor property of the new ClaimsIdentity object is not equal to the Actor property of the constructor’s IIdentity argument. In the .NET Framework 4.6.1 and earlier versions, it is equal.
Suggestion If this behavior is undesirable, you can restore the previous behavior by setting the Switch.System.Security.ClaimsIdentity.SetActorAsReferenceWhenCopyingClaimsIdentity switch in your application configuration file to true. This requires that you add the following to the <runtime> section of your web.config file:

<configuration>
<runtime>
<AppContextSwitchOverrides value="Switch.System.Security.ClaimsIdentity.SetActorAsReferenceWhenCopyingClaimsIdentity=true" />
</runtime>
</configuration>
Scope Edge
Version ۴٫۶٫۲
Type Retargeting
Affected APIs

Change in path separator character in FullName property of ZipArchiveEntry objects

Details For apps that target the .NET Framework 4.6.1 and later versions, the path separator character has changed from a backslash (“”) to a forward slash (“/”) in the FullName property of ZipArchiveEntry objects created by overloads of the CreateFromDirectory method. The change brings the .NET implementation into conformity with section 4.4.17.1 of the .ZIP File Format Specification and allows .ZIP archives to be decompressed on non-Windows systems.Decompressing a zip file created by an app that targets a previous version of the .NET Framework on non-Windows operating systems such as the Macintosh fails to preserve the directory structure. For example, on the Macintosh, it creates a set of files whose filename concatenates the directory path, along with any backslash (“”) characters, and the filename. As a result, the directory structure of decompressed files is not preserved.
Suggestion The impact of this change on .ZIP files that are decompressed on the Windows operating system by APIs in the .NET Framework System.IO namespace should be minimal, since these APIs can seamlessly handle either a slash (“/”) or a backslash (“&quot;) as the path separator character.If this change is undesirable, you can opt out of it by adding a configuration setting to the <runtime> section of your application configuration file. The following example shows both the <runtime> section and the Switch.System.IO.Compression.ZipFile.UseBackslash opt-out switch:

<runtime>
<AppContextSwitchOverrides value="Switch.System.IO.Compression.ZipFile.UseBackslash=true" />
</runtime>

In addition, apps that target previous versions of the .NET Framework but are running on the .NET Framework 4.6.1 and later versions can opt in to this behavior by adding a configuration setting to the <runtime> section of the application configuration file. The following shows both the <runtime> section and the Switch.System.IO.Compression.ZipFile.UseBackslash opt-in switch.

<runtime>
<AppContextSwitchOverrides value="Switch.System.IO.Compression.ZipFile.UseBackslash=false" />
</runtime>
Scope Edge
Version ۴٫۶٫۱
Type Retargeting
Affected APIs

Changes in path normalization

Details Starting with apps that target the .NET Framework 4.6.2, the way in which the runtime normalizes paths has changed.Normalizing a path involves modifying the string that identifies a path or file so that it conforms to a valid path on the target operating system. Normalization typically involves:

  • Canonicalizing component and directory separators.
  • Applying the current directory to a relative path.
  • Evaluating the relative directory (.) or the parent directory (..) in a path.
  • Trimming specified characters.

Starting with apps that target the .NET Framework 4.6.2, the following changes in path normalization are enabled by default:

  • The runtime defers to the operating system’s GetFullPathName function to normalize paths.
  • Normalization no longer involves trimming the end of directory segments (such as a space at the end of a directory name).
  • Support for device path syntax in full trust, including .</code> and, for file I/O APIs in mscorlib.dll, '?'.
  • The runtime does not validate device syntax paths.
  • The use of device syntax to access alternate data streams is supported.

These changes improve performance while allowing methods to access previously inaccessible paths. Apps that target the .NET Framework 4.6.1 and earlier versions but are running under the .NET Framework 4.6.2 or later are unaffected by this change.

Suggestion Apps that target the .NET Framework 4.6.2 or later can opt out of this change and use legacy normalization by adding the following to the <runtime> section of the application configuration file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.IO.UseLegacyPathHandling=true" />
</runtime>

Apps that target the .NET Framework 4.6.1 or earlier but are running on the .NET Framework 4.6.2 or later can enable the changes to path normalization by adding the following line to the <runtime> section of the application .configuration file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.IO.UseLegacyPathHandling=false" />
</runtime>
Scope Minor
Version ۴٫۶٫۲
Type Retargeting

Foreach iterator variable is now scoped within the iteration, so closure capturing semantics are different (in C#5)

Details Beginning with C# 5 (Visual Studio 2012), foreach iterator variables are scoped within the iteration. This can cause breaks if code was previously depending on the variables to not be included in the foreach‘s closure. The symptom of this change is that an iterator variable passed to a delegate is treated as the value it has at the time the delegate is created, rather than the value it has at the time the delegate is invoked.
Suggestion Ideally, code should be updated to expect the new compiler behavior. If the old semantics are required, the iterator variable can be replaced with a separate variable which is explicitly placed outside of the loop’s scope.
Scope Major
Version ۴٫۵
Type Retargeting

IAsyncResult.CompletedSynchronously property must be correct for the resulting task to complete

Details When calling TaskFactory.FromAsync, the implementation of the CompletedSynchronously property must be correct for the resulting task to complete. That is, the property must return true if, and only if, the implementation completed synchronously. Previously, the property was not checked.
Suggestion If IAsyncResult implementations correctly return true for the CompletedSynchronously property only when a task completed synchronously, then no break will be observed. Users should review IAsyncResult implementations they own (if any) to ensure that they correctly evaluate whether a task completed synchronously or not.
Scope Edge
Version ۴٫۵
Type Retargeting
Affected APIs

List<T>.ForEach can throw exception when modifying list item

Details Beginning in .NET 4.5, a ForEach(Action<T>) enumerator will throw an InvalidOperationException exception if an element in the calling collection is modified. Previously, this would not throw an exception but could lead to race conditions.
Suggestion Ideally, code should be fixed to not modify lists while enumerating their elements because that is never a safe operation. To revert to the previous behavior, though, an app may target .NET 4.0.
Scope Edge
Version ۴٫۵
Type Retargeting
Affected APIs

Long path support

Details Starting with apps that target the .NET Framework 4.6.2, long paths (of up to 32K characters) are supported, and the 260-character (or MAX_PATH) limitation on path lengths has been removed.For apps that are recompiled to target the .NET Framework 4.6.2, code paths that previously threw a PathTooLongException because a path exceeded 260 characters will now throw a PathTooLongException only under the following conditions:

  • The length of the path is greater than MaxValue (32,767) characters.
  • The operating system returns COR_E_PATHTOOLONG or its equivalent.

For apps that target the .NET Framework 4.6.1 and earlier versions, the runtime automatically throws a PathTooLongException whenever a path exceeds 260 characters.

Suggestion For apps that target the .NET Framework 4.6.2, you can opt out of long path support if it is not desirable by adding the following to the <runtime> section of your app.config file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.IO.BlockLongPaths=true" />
</runtime>

For apps that target earlier versions of the .NET Framework but run on the .NET Framework 4.6.2 or later, you can opt in to long path support by adding the following to the <runtime> section of your app.config file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.IO.BlockLongPaths=false" />
</runtime>
Scope Minor
Version ۴٫۶٫۲
Type Retargeting

ObsoleteAttribute exports as both ObsoleteAttribute and DeprecatedAttribute in WinMD scenarios

Path colon checks are stricter

Details In .NET Framework 4.6.2, a number of changes were made to support previously unsupported paths (both in length and format). Checks for proper drive separator (colon) syntax were made more correct, which had the side effect of blocking some URI paths in a few select Path APIs where they used to be tolerated.
Suggestion If passing a URI to affected APIs, modify the string to be a legal path first.

  • Remove the scheme from URLs manually (e.g. remove file:// from URLs)
  • Pass the URI to the Uri class and use LocalPath

Alternatively, you can opt out of the new path normalization by setting the Switch.System.IO.UseLegacyPathHandling AppContext switch to true.

Scope Edge
Version ۴٫۶٫۲
Type Retargeting
Affected APIs

System.Uri parsing adheres to RFC 3987

Details URI parsing has changed in several ways in .NET 4.5. Note, however, that these changes only affect code targeting .NET 4.5. If a binary targets .NET 4.0, the old behavior will be observed. Changes to URI parsing in .NET 4.5 include:

  • URI parsing will perform normalization and character checking according to the latest IRI rules in RFC 3987.
  • Unicode normalization form C will only be performed on the host portion of the URI.
  • Invalid mailto: URIs will now cause an exception.
  • Trailing dots at the end of a path segment are now preserved.
  • file:// URIs do not escape the ? character.
  • Unicode control characters U+0080 through U+009F are not supported.
  • Comma characters , or %2c are not automatically unescaped.
Suggestion If the old .NET 4.0 URI parsing semantics are necessary (they often aren’t), they can be used by targeting .NET 4.0. This can be accomplished by using a TargetFrameworkAttribute on the assembly, or through Visual Studio’s project system UI in the ‘project properties’ page.
Scope Major
Version ۴٫۵
Type Retargeting
Affected APIs

System.Uri.IsWellFormedUriString method returns false for relative URIs with a colon char in first segment

Details Beginning with the .NET Framework 4.5, IsWellFormedUriString(String, UriKind) will treat relative URIs with a : in their first segment as not well formed. This is a change from IsWellFormedUriString(String, UriKind) behavior in the .NET Framework 4.0 that was made to conform to RFC3986.
Suggestion This change (like many other URI changes) will only affect applications targeting the .NET Framework 4.5 (or later). To keep using the old behavior, target the app against the .NET Framework 4.0. Alternatively, scan URI’s prior to calling IsWellFormedUriString(String, UriKind) looking for : characters that you may want to remove for validation purposes, if the old behavior is desirable.
Scope Minor
Version ۴٫۵
Type Retargeting
Affected APIs

Entity Framework

Entity Framework version must match the .NET Framework version

Details The entity framework version should be matched with the .NET framework version. Entity Framework 5 is recommended for .NET 4.5. There are some known issues with EF 4.x in a .NET 4.5 project around System.ComponentModel.DataAnnotations. In .NET 4.5, these were moved to a different assembly, so there are issues determining which annotations to use.
Suggestion Upgrade to Entity Framework 5 for .NET Framework 4.5
Scope Major
Version ۴٫۵
Type Retargeting

JIT

IL ret not allowed in a try region

Details Unlike the JIT64 just-in-time compiler, RyuJIT (used in .NET 4.6) does not allow an IL ret instruction in a try region. Returning from a try region is disallowed by the ECMA-335 specification, and no known managed compiler generates such IL. However, the JIT64 compiler will execute such IL if it is generated using reflection emit.
Suggestion If an app is generating IL that includes a ret opcode in a try region, the app may target .NET 4.5 to use the old JIT and avoid this break. Alternatively, the generated IL may be updated to return after the try region.
Scope Edge
Version ۴٫۶
Type Retargeting

New 64-bit JIT compiler in the .NET Framework 4.6

Details Starting with the .NET Framework 4.6, a new 64-bit JIT compiler is used for just-in-time compilation. In some cases, an unexpected exception is thrown or a different behavior is observed than if an app is run using the 32-bit compiler or the older 64-bit JIT compiler. This change does not affect the 32-bit JIT compiler.The known differences include the following:

  • Under certain conditions, an unboxing operation may throw a NullReferenceException in Release builds with optimization turned on.
  • In some cases, execution of production code in a large method body may throw a StackOverflowException.
  • Under certain conditions, structures passed to a method are treated as reference types rather than as value types in Release builds. One of the manifestations of this issue is that the individual items in a collection appear in an unexpected order.
  • Under certain conditions, the comparison of UInt16 values with their high bit set is incorrect if optimization is enabled.
  • Under certain conditions, particularly when initializing array values, memory initialization by the OpCodes.Initblk IL instruction may initialize memory with an incorrect value. This can result either in an unhandled exception or incorrect output.
  • Under certain rare conditions, a conditional bit test can return the incorrect Boolean value or throw an exception if compiler optimizations are enabled.
  • Under certain conditions, if an if statement is used to test for a condition before entering a try block and in the exit from the try block, and the same condition is evaluated in the catch or finally block, the new 64-bit JIT compiler removes the if condition from the catch or finally block when it optimizes code. As a result, code inside the if statement in the catch or finally block is executed unconditionally.
Suggestion Mitigation of known issues If you encounter the issues listed above, you can address them by doing any of the following:

  • Upgrade to the .NET Framework 4.6.2. The new 64-bit compiler included with the .NET Framework 4.6.2 addresses each of these known issues.
  • Ensure that your version of Windows is up to date by running Windows Update. Service updates to the .NET Framework 4.6 and 4.6.1 address each of these issues except the NullReferenceException in an unboxing operation.
  • Compile with the older 64-bit JIT compiler. See the Mitigation of other issues section for more information on how to do this.

Mitigation of other issues If you encounter any other difference in behavior between code compiled with the older 64-bit compiler and the new 64-bit JIT compiler, or between the debug and release versions of your app that are both compiled with the new 64-bit JIT compiler, you can do the following to compile your app with the older 64-bit JIT compiler:

  • On a per-application basis, you can add the <useLegacyJit> element to your application’s configuration file. The following disables compilation with the new 64-bit JIT compiler and instead uses the legacy 64-bit JIT compiler.
<?xml version ="1.0"?>
<configuration>
<runtime>
<useLegacyJit enabled="1" />
</runtime>
</configuration>
  • On a per-user basis, you can add a REG_DWORD value named useLegacyJit to the HKEY_CURRENT_USERSOFTWAREMicrosoft.NETFramework key of the registry. A value of 1 enables the legacy 64-bit JIT compiler; a value of 0 disables it and enables the new 64-bit JIT compiler.
  • On a per-machine basis, you can add a REG_DWORD value named useLegacyJit to the HKEY_LOCAL_MACHINESOFTWAREMicrosoft.NETFramework key of the registry. A value of 1 enables the legacy 64-bit JIT compiler; a value of 0 disables it and enables the new 64-bit JIT compiler.

You can also let us know about the problem by reporting a bug on Microsoft Connect.

Scope Edge
Version ۴٫۶
Type Retargeting

MSBuild

ResolveAssemblyReference task now warns of dependencies with the wrong architecture

Details The task emits a warning, MSB3270, which indicates that a reference or any of its dependencies does not match the app’s architecture. For example, this occurs if an app that was compiled with the AnyCPU option includes an x86 reference. Such a scenario could result in an app failure at run time (in this case, if the app is deployed as an x64 process).
Suggestion There are two areas of impact:

  • Recompilation generates warnings that did not appear when the app was compiled under a previous version of MSBuild. However, because the warning identifies a possible source of runtime failure, it should be investigated and addressed.
  • If warnings are treated as errors, the app will fail to compile.
Scope Minor
Version ۴٫۵٫۱
Type Retargeting

Networking

Certificate EKU OID validation

Default value of ServicePointManager.SecurityProtocol is SecurityProtocolType.System.Default

Details Starting with apps that target the .NET Framework 4.7, the default value of the ServicePointManager.SecurityProtocol property is SecurityProtocolType.SystemDefault. This change allows .NET Framework networking APIs based on SslStream (such as FTP, HTTPS, and SMTP) to inherit the default security protocols from the operating system instead of using hard-coded values defined by the .NET Framework. The default varies by operating system and any custom configuration performed by the system administrator. For information on the default SChannel protocol in each version of the Windows operating system, see Protocols in TLS/SSL (Schannel SSP).For applications that target an earlier version of the .NET Framework, the default value of the ServicePointManager.SecurityProtocol property depends on the version of the .NET Framework targeted. See the Networking section of Retargeting Changes for Migration from .NET Framework 4.5.2 to 4.6 for more information.
Suggestion This change affects applications that target the .NET Framework 4.7 or later versions.If you prefer to use a defined protocol rather than relying on the system default, you can explicitly set the value of the ServicePointManager.SecurityProtocol property.If this change is undesirable, you can opt out of it by adding a configuration setting to the <runtime> section of your application configuration file. The following example shows both the <runtime> section and the Switch.System.Net.DontEnableSystemDefaultTlsVersions opt-out switch:

<runtime>
<AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=true" />
</runtime>
Scope Minor
Version ۴٫۷
Type Retargeting
Affected APIs

Only Tls 1.0, 1.1 and 1.2 protocols supported in System.Net.ServicePointManager and System.Net.Security.SslStream

Details Starting with the .NET Framework 4.6, the ServicePointManager and SslStream classes are only allowed to use one of the following three protocols: Tls1.0, Tls1.1, or Tls1.2. The SSL3.0 protocol and RC4 cipher are not supported.
Suggestion The recommended mitigation is to upgrade the sever-side app to Tls1.0, Tls1.1, or Tls1.2. If this is not feasible, or if client apps are broken, the AppContext class can be used to opt out of this feature in either of two ways:

  1. By programmatically setting compat switches on the AppContext, as explained here
  2. By adding the following line to the <runtime> section of the app.config file: <AppContextSwitchOverrides value="Switch.System.Net.DontEnableSchUseStrongCrypto=true"/>;
Scope Minor
Version ۴٫۶
Type Retargeting
Affected APIs

SslStream supports TLS Alerts

Details After a failed TLS handshake, an IOException with an inner Win32Exception exception will be thrown by the first I/O Read/Write operation. The NativeErrorCode code for the Win32Exception can be mapped to the TLS Alert from the remote party using this Schannel documentation.For more information, see RFC 2246: Section 7.2.2 Error alertsThe behavior in .NET 4.6.2 and below is that the transport channel (usually TCP connection) will timeout during either Write or Read if the other party failed the handshake and immediately afterwards rejected the connection.
Suggestion Applications calling network I/O APIs such as Read(Byte[], Int32, Int32)/Write(Byte[], Int32, Int32) should handle IOException or TimeoutException.The TLS Alerts feature is enabled by default starting with .NET 4.7. Applications targeting .NET 4.0 – .NET 4.6.2 running on a .NET 4.7 or higher system will have the feature disabled to preserve compatibility.The following configuration API is available to enable or disable the feature for .NET 4.6 and above applications running on .NET 4.7 or higher framework.Must be the very first thing the application does since ServicePointManager will initialize only once:

AppContext.SetSwitch("TestSwitch.LocalAppContext.DisableCaching", true);
AppContext.SetSwitch("Switch.System.Net.DontEnableTlsAlerts", true); // Set to 'false' to enable the feature in .NET 4.6 - 4.6.2.
<runtime>
<AppContextSwitchOverrides value="Switch.System.Net.DontEnableTlsAlerts=true"/>
<!-- Set to 'false' to enable the feature in .NET 4.6 - 4.6.2. -->
</runtime>
  • Registry key (machine global):

Set the Value to ‘false’ to enable the feature in .NET 4.6 – 4.6.2.

Key = HKLMSOFTWARE[Wow6432Node]Microsoft.NETFrameworkAppContextSwitch.System.Net.DontEnableTlsAlerts
Type = String
Value = "true"
Scope Edge
Version ۴٫۷
Type Retargeting
Affected APIs

TLS 1.x by default passes the SCH_SEND_AUX_RECORD flag to the underlying SCHANNEL API

Details When using TLS 1.x, the .NET Framework relies on the underlying Windows SCHANNEL API. Starting with .NET Framework 4.6, the SCH_SEND_AUX_RECORD flag is passed by default to SCHANNEL. This causes SCHANNEL to split data to be encrypted into two separate records, the first as a single byte and the second as n-1 bytes.In rare cases, this breaks communication between clients and existing servers that make the assumption that the data resides in a single record.
Suggestion If this change breaks communication with an existing server, you can disable sending the SCH_SEND_AUX_RECORD flag and restore the previous behavior of not splitting data into separate records by adding the following switch to the <AppContextSwitchOverrides> in the ` of your app configuration file:

<runtime>
<AppContextSwitchOverrides
value="Switch.System.Net.DontEnableSchSendAuxRecord=true" />
</runtime>

[!IMPORTANT] This setting is provided for backward compatibility only. Its use is otherwise not recommended.

Scope Edge
Version ۴٫۶
Type Retargeting
Affected APIs

Security

CspParameters.ParentWindowHandle now expects HWND value

Details The ParentWindowHandle value, introduced in .NET Framework 2.0, allows an application to register a parent window handle value such that any UI required to access the key (such as a PIN prompt or consent dialog) opens as a modal child to the specified window.Starting with apps that target the .NET Framework 4.7, a Windows Forms application can set the ParentWindowHandle property with code like the following:

cspParameters.ParentWindowHandle = form.Handle;

In previous versions of the .NET Framework, the value was expected to be an IntPtr representing a location in memory where the HWND value resided. Setting the property to form.Handle on Windows 7 and earlier versions had no effect, but on Windows 8 and later versions, it results in a “CryptographicException: The parameter is incorrect.”

Suggestion Applications targeting .NET 4.7 or higher wishing to register a parent window relationship are encouraged to use the simplified form:

cspParameters.ParentWindowHandle = form.Handle;

Users who had identified that the correct value to pass was the address of a memory location which held the value form.Handle can opt out of the behavior change by setting the AppContext switch Switch.System.Security.Cryptography.DoNotAddrOfCspParentWindowHandle to true.

  1. By programmatically setting compat switches on the AppContext, as explained here
  2. By adding the following line to the <runtime> section of the app.config file:
<runtime>
<AppContextSwitchOverrides value="Switch.System.Security.Cryptography.DoNotAddrOfCspParentWindowHandle=true"/>
</runtime>

Conversely, users who wish to opt in to the new behavior on the .NET Framework 4.7 runtime when the application loads under older .NET Framework versions can set the AppContext switch to false.

Scope Minor
Version ۴٫۷
Type Retargeting
Affected APIs

RSACng now correctly loads RSA keys of non-standard key size

SignedXml.GetPublicKey returns RSACng on net462 (or lightup) without retargeting change

Details Starting with the .NET Framework 4.6.2, the concrete type of the object returned by the SignedXml.GetPublicKey method changed (without a quirk) from a CryptoServiceProvider implementation to a Cng implementation. This is because the implementation changed from using certificate.PublicKey.Key to using the internal certificate.GetAnyPublicKey which forwards to RSACertificateExtensions.GetRSAPublicKey.
Suggestion Starting with apps running on the .NET Framework 4.7.1, you can use the CryptoServiceProvider implementation used by default in the .NET Framework 4.6.1 and earlier versions by adding the following configuration switch to the runtime section of your app config file:

<AppContextSwitchOverrides value="Switch.System.Security.Cryptography.Xml.SignedXmlUseLegacyCertificatePrivateKey=true" />
Scope Edge
Version ۴٫۶٫۲
Type Retargeting
Affected APIs

SslStream supports TLS Alerts

Details After a failed TLS handshake, an IOException with an inner Win32Exception exception will be thrown by the first I/O Read/Write operation. The NativeErrorCode code for the Win32Exception can be mapped to the TLS Alert from the remote party using this Schannel documentation.For more information, see RFC 2246: Section 7.2.2 Error alertsThe behavior in .NET 4.6.2 and below is that the transport channel (usually TCP connection) will timeout during either Write or Read if the other party failed the handshake and immediately afterwards rejected the connection.
Suggestion Applications calling network I/O APIs such as Read(Byte[], Int32, Int32)/Write(Byte[], Int32, Int32) should handle IOException or TimeoutException.The TLS Alerts feature is enabled by default starting with .NET 4.7. Applications targeting .NET 4.0 – .NET 4.6.2 running on a .NET 4.7 or higher system will have the feature disabled to preserve compatibility.The following configuration API is available to enable or disable the feature for .NET 4.6 and above applications running on .NET 4.7 or higher framework.Must be the very first thing the application does since ServicePointManager will initialize only once:

AppContext.SetSwitch("TestSwitch.LocalAppContext.DisableCaching", true);
AppContext.SetSwitch("Switch.System.Net.DontEnableTlsAlerts", true); // Set to 'false' to enable the feature in .NET 4.6 - 4.6.2.
<runtime>
<AppContextSwitchOverrides value="Switch.System.Net.DontEnableTlsAlerts=true"/>
<!-- Set to 'false' to enable the feature in .NET 4.6 - 4.6.2. -->
</runtime>
  • Registry key (machine global):

Set the Value to ‘false’ to enable the feature in .NET 4.6 – 4.6.2.

Key = HKLMSOFTWARE[Wow6432Node]Microsoft.NETFrameworkAppContextSwitch.System.Net.DontEnableTlsAlerts
Type = String
Value = "true"
Scope Edge
Version ۴٫۷
Type Retargeting
Affected APIs

Visual Basic .NET

VB.NET no longer supports partial namespace qualification for System.Windows APIs

Details Beginning in .NET 4.5.2, VB.NET projects cannot specify System.Windows APIs with partially-qualified namespaces. For example, referring to Windows.Forms.DialogResult will fail. Instead, code must refer to the fully qualified name (DialogResult) or import the specific namespace and refer simply to DialogResult.
Suggestion Code should be updated to refer to System.Windows APIs either with simple names (and importing the relevant namespace) or with fully qualified names.
Scope Minor
Version ۴٫۵٫۲
Type Retargeting

Windows Communication Foundation (WCF)

Calling CreateDefaultAuthorizationContext with a null argument has changed

Details The implementation of the AuthorizationContext returned by a call to the <xref:System.IdentityModel.Policy.AuthorizationContext.CreateDefaultAuthorizationContext(System.Collections.Generic.IListSystem.IdentityModel.Policy.IAuthorizationPolicy)?displayProperty=name> with a null authorizationPolicies argument has changed its implementation in the .NET Framework 4.6.
Suggestion In rare cases, WCF apps that use custom authentication may see behavioral differences. In such cases, the previous behavior can be restored in either of two ways:

  1. Recompile your app to target an earlier version of the .NET Framework than 4.6. For IIS-hosted services, use the <httpRuntime targetFramework=”x.x” /> element to target an earlier version of the .NET Framework.
  2. Add the following line to the <appSettings> section of your app.config file: <add key="appContext.SetSwitch:Switch.System.IdentityModel.EnableCachedEmptyDefaultAuthorizationContext" value="true" />
Scope Minor
Version ۴٫۶
Type Retargeting
Affected APIs
  • <xref:System.IdentityModel.Policy.AuthorizationContext.CreateDefaultAuthorizationContext(System.Collections.Generic.IListSystem.IdentityModel.Policy.IAuthorizationPolicy)?displayProperty=nameWithType>

Deadlock may result when using Reentrant services

Details A deadlock may result in a Reentrant service, which restricts instances of the service to one thread of execution at a time. Services prone to encounter this problem will have the following ServiceBehaviorAttribute in their code:

[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant)]
Suggestion To address this issue, you can do the following:

  • Set the service’s concurrency mode to ConcurrencyMode.Single or <System.ServiceModel.ConcurrencyMode.Multiple?displayProperty=nameWithType>. For example:
[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Single)]
  • Install the latest update to the .NET Framework 4.6.2, or upgrade to a later version of the .NET Framework. This disables the flow of the ExecutionContext in OperationContext.Current. This behavior is configurable; it is equivalent to adding the following app setting to your configuration file:
<appSettings>
<add key="Switch.System.ServiceModel.DisableOperationContextAsyncFlow" value="true" />
</appSettings>

The value of 'Switch.System.ServiceModel.DisableOperationContextAsyncFlow' should never be set to 'false' for Rentrant services.
Scope Minor
Version ۴٫۶٫۲
Type Retargeting
Affected APIs

OperationContext.Current may return null when called in a using clause

Details OperationContext.Current may return null and a NullReferenceException may result if all of the following conditions are true:

using (new OperationContextScope(OperationContext.Current))

OperationContext context = OperationContext.Current;      // OperationContext.Current is null.
// ...

Suggestion To address this issue, you can do the following:

  • Modify your code as follows to instantiate a new non-null Current object:
OperationContext ocx = OperationContext.Current;
using (new OperationContextScope(OperationContext.Current))

OperationContext.Current = new OperationContext(ocx.Channel);
// ...

  • Install the latest update to the .NET Framework 4.6.2, or upgrade to a later version of the .NET Framework. This disables the flow of the ExecutionContext in OperationContext.Current and restores the behavior of WCF applications in the .NET Framework 4.6.1 and earlier versions. This behavior is configurable; it is equivalent to adding the following app setting to your configuration file:
<appSettings>
<add key="Switch.System.ServiceModel.DisableOperationContextAsyncFlow" value="true" />
</appSettings>

If this change is undesirable and your application depends on execution context flowing between operation contexts, you can enable its flow as follows:

<appSettings>
<add key="Switch.System.ServiceModel.DisableOperationContextAsyncFlow" value="false" />
</appSettings>
Scope Edge
Version ۴٫۶٫۲
Type Retargeting
Affected APIs

Serialization of control characters with DataContractJsonSerializer is now compatible with ECMAScript V6 and V8

Details In the .NET framework 4.6.2 and earlier versions, the DataContractJsonSerializer did not serialize some special control characters, such as b, f, and t, in a way that was compatible with the ECMAScript V6 and V8 standards. Starting with the .NET Framework 4.7, serialization of these control characters is compatible with ECMAScript V6 and V8.
Suggestion For apps that target the .NET Framework 4.7, this feature is enabled by default. If this behavior is not desirable, you can opt out of this feature by adding the following line to the <runtime> section of the app.config or web.config file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.Runtime.Serialization.DoNotUseECMAScriptV6EscapeControlCharacter=false" />
</runtime>
Scope Edge
Version ۴٫۷
Type Retargeting
Affected APIs

WCF binding with the TransportWithMessageCredential security mode

Details Beginning in the .NET Framework 4.6.1, WCF binding that uses the TransportWithMessageCredential security mode can be set up to receive messages with unsigned “to” headers for asymmetric security keys.By default, unsigned “to” headers will continue to be rejected in .NET 4.6.1. They will only be accepted if an application opts into this new mode of operation using the Switch.System.ServiceModel.AllowUnsignedToHeader configuration switch.Because this is an opt-in feature, it should not affect the behavior of existing apps.
Suggestion Because this is an opt-in feature, it should not affect the behavior of existing apps. To control whether the new behavior is used or not, use the following configuration setting:

<runtime>
<AppContextSwitchOverrides value="Switch.System.ServiceModel.AllowUnsignedToHeader=true" />
</runtime>
Scope Transparent
Version ۴٫۶٫۱
Type Retargeting
Affected APIs

WCF message security now is able to use TLS1.1 and TLS1.2

Details Starting in the .NET Framework 4.7, customers can configure either TLS1.1 or TLS1.2 in WCF message security in addition to SSL3.0 and TLS1.0 through application configuration settings.
Suggestion In the .NET Framework 4.7, support for TLS1.1 and TLS1.2 in WCF message security is disabled by default. You can enable it by adding the following line to the <runtime> section of the app.config or web.config file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.ServiceModel.DisableUsingServicePointManagerSecurityProtocols=false;Switch.System.Net.DontEnableSchUseStrongCrypto=false" />
</runtime>
Scope Edge
Version ۴٫۷
Type Retargeting

WCF transport security supports certificates stored using CNG

Details Starting with apps that target the .NET Framework 4.6.2, WCF transport security supports certificates stored using the Windows Cryptography Library (CNG). This support is limited to certificates with a public key that has an exponent no more than 32 bits in length. When an application targets the .NET Framework 4.6.2, this feature is on by default.In earlier versions of the .NET Framework, the attempt to use X509 certificates with a CSG key storage provider throws an exception.
Suggestion Apps that target the .NET Framework 4.6.1 and earlier but are running on the .NET Framework 4.6.2 can enable support for CNG certificates by adding the following line to the <runtime> section of the app.config or web.config file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.ServiceModel.DisableCngCertificates=false" />
</runtime>

This can also be done programmatically with the following code:

private const string DisableCngCertificates = @"Switch.System.ServiceModel.DisableCngCertificate";
AppContext.SetSwitch(disableCngCertificates, false);
Const DisableCngCertificates As String = "Switch.System.ServiceModel.DisableCngCertificates"
AppContext.SetSwitch(disableCngCertificates, False)

Note that, because of this change, any exception handling code that depends on the attempt to initiate secure communication with a CNG certificate to fail will no longer execute.

Scope Minor
Version ۴٫۶٫۲
Type Retargeting

X509CertificateClaimSet.FindClaims Considers All claimTypes

Details In apps that target the .NET Framework 4.6.1, if an X509 claim set is initialized from a certificate that has multiple DNS entries in its SAN field, the FindClaims(String, String) method attempts to match the claimType argument with all the DNS entries.For apps that target previous versions of the .NET Framework, the FindClaims(String, String) method attempts to match the claimType argument only with the last DNS entry.
Suggestion This change only affects applications targeting the .NET Framework 4.6.1. This change may be disabled (or enabled if targetting pre-4.6.1) with the DisableMultipleDNSEntries compatibility switch.
Scope Minor
Version ۴٫۶٫۱
Type Retargeting
Affected APIs

Windows Forms

Application.FilterMessage no longer throws for re-entrant implementations of IMessageFilter.PreFilterMessage

DataObject.GetData now retrieves data as UTF-8

Details For apps that target the .NET Framework 4 or that run on the .NET Framework 4.5.1 or earlier versions, DataObject.GetData retrieves HTML-formatted data as an ASCII string. As a result, non-ASCII characters (characters whose ASCII codes are greater than 0x7F) are represented by two random characters.For apps that target the .NET Framework 4.5 or later and run on the .NET Framework 4.5.2, DataObject.GetData retrieves HTML-formatted data as UTF-8, which represents characters greater than 0x7F correctly.
Suggestion If you implemented a workaround for the encoding problem with HTML-formatted strings (for example, by explicitly encoding the HTML string retrieved from the Clipboard by passing it to GetString(Byte[], Int32, Int32)) and you’re retargeting your app from version 4 to 4.5, that workaround should be removed.If the old behavior is needed for some reason, the app can target the .NET Framework 4.0 to get that behavior.
Scope Edge
Version ۴٫۵٫۲
Type Retargeting
Affected APIs

EncoderParameter ctor is obsolete

Details The EncoderParameter(Encoder, Int32, Int32, Int32, Int32) constructor is obsolete now and will introduce build warnings if used.
Suggestion Although the EncoderParameter(Encoder, Int32, Int32, Int32, Int32)constructor will continue to work, the following constructor should be used instead to avoid the obsolete build warning when re-compiling code with .NET 4.5 tools: EncoderParameter(Encoder, Int32, EncoderParameterValueType, IntPtr).
Scope Minor
Version ۴٫۵
Type Retargeting
Affected APIs

Icon.ToBitmap successfully converts icons with PNG frames into Bitmap objects

Details Starting with the apps that target the .NET Framework 4.6, the Icon.ToBitmap method successfully converts icons with PNG frames into Bitmap objects.In apps that target the .NET Framework 4.5.2 and earlier versions, the Icon.ToBitmap method throws an ArgumentOutOfRangeException exception if the Icon object has PNG frames.This change affects apps that are recompiled to target the .NET Framework 4.6 and that implement special handling for the ArgumentOutOfRangeException that is thrown when an Icon object has PNG frames. When running under the .NET Framework 4.6, the conversion is successful, an ArgumentOutOfRangeException is no longer thrown, and therefore the exception handler is no longer invoked.
Suggestion If this behavior is undesirable, you can retain the previous behavior by adding the following element to the <runtime> section of your app.config file:

<AppContextSwitchOverrides
value="Switch.System.Drawing.DontSupportPngFramesInIcons=true" />

If the app.config file already contains the AppContextSwitchOverrides element, the new value should be merged with the value attribute like this:

<AppContextSwitchOverrides
value="Switch.System.Drawing.DontSupportPngFramesInIcons=true;<previous key>=<previous value>" />
Scope Minor
Version ۴٫۶
Type Retargeting
Affected APIs

Incorrect implementation of MemberDescriptor.Equals

Details Original implementation of “Equals” method was comparing two different string properties from the objects under comparison: category name to description string. The fix is to compare “category” of first object to “category” of the second one and “description” to “description”. MemberDescriptorEqualsReturnsFalseIfEquivalent configuration value can be set to true to opt out of the new behavior if targeting 4.6.2 or to false to enable this fix when targeting framework version is below 4.6.2.
Suggestion If your application depends on MemberDescriptor.Equals sometimes returning false when descriptors are equivalent, and you are targeting 4.6.2 version of the .NET Framework, you have several options:

  1. Make code changes to compare “category” and “description” fields manually in addition to running Equals method.
  2. Opt out from this change by adding the following value to the app.config file:
<runtime>
<AppContextSwitchOverrides value="Switch.System.MemberDescriptorEqualsReturnsFalseIfEquivalent=true" />
</runtime>

If your application targets 4.6.1 or lower version of the .NET Framework, and you want this change enabled, you can set the compatibility switch to false by adding the following value to the app.config file:

<runtime>
<AppContextSwitchOverrides value="Switch.System.MemberDescriptorEqualsReturnsFalseIfEquivalent=false" />
</runtime>
Scope Edge
Version ۴٫۶٫۲
Type Retargeting
Affected APIs

Windows Presentation Foundation (WPF)

NullReferenceException in exception handling code from ImageSourceConverter.ConvertFrom

Two-way data-binding to a property with a non-public setter is not supported

Details Attempting to data bind to a property without a public setter has never been a supported scenario. Beginning in the .NET Framework 4.5.1, this scenario will throw an InvalidOperationException. Note that this new exception will only be thrown for apps that specifically target the .NET Framework 4.5.1. If an app targets the .NET Framework 4.5, the call will be allowed. If the app does not target a particular .NET Framework version, the binding will be treated as one-way.
Suggestion The app should be updated to either use one-way binding, or expose the property’s setter publicly. Alternatively, targeting the .NET Framework 4.5 will cause the app to exhibit the old behavior.
Scope Minor
Version ۴٫۵٫۱
Type Retargeting
Affected APIs

WPF Grid allocation of space to star-columns

Details Starting with the .NET Framework 4.7, WPF replaces the algorithm that Grid uses to allocate space to *-columns. This will change the actual width assigned to *-columns in a number of cases:

  • When one or more *-columns also have a minimum or maximum width that overrides the proportional allocation for that colum. (The minimum width can derive from an explicit MinWidth declaration, or from an implicit minimum obtained from the column’s content. The maximum width can only be defined explicitly, from a MaxWidth declaration.)
  • When one or more *-columns declare an extremely large *-weight, greater than 10^298.
  • When the *-weights are sufficiently different to encounter floating-point instability (overflow, underflow, loss of precision).
  • When layout rounding is enabled, and the effective display DPI is sufficiently high.

In the first two cases, the widths produced by the new algorithm can be significantly different from those produced by the old algorithm; in the last case, the difference will be at most one or two pixels.The new algorithm fixes several bugs present in the old algorithm:

  1. Total allocation to columns can exceed the Grid’s width. This can occur when allocating space to a column whose proportional share is less than its minimum size. The algorithm allocates the minimum size, which decreases the space available to other columns. If there are no *-columns left to allocate, the total allocation will be too large.
  2. Total allocation can fall short of the Grid’s width. This is the dual problem to #1, arising when allocating to a column whose proportional share is greater than its maximum size, with no *-columns left to take up the slack.
  3. Two *-columns can receive allocations not proportional to their *-weights. This is a milder version of #1/#2, arising when allocating to *-columns A, B, and C (in that order), where B’s proportional share violates its min (or max) constraint. As above, this changes the space available to column C, who gets less (or more) proportional allocation than A did,
  4. Columns with extremely large weights (> 10^298) are all treated as if they had weight 10^298. Proportional differences between them (and between columns with slightly smaller weights) are not honored.
  5. Columns with inifinte weights are not handled correctly. [Actually you can’t set a weight to Infinity, but this is an artificial restriction. The allocation code was trying to handle it, but doing a bad job.]
  6. Several minor problems while avoiding overflow, underflow, loss of precision and similar floating-point issues.
  7. Adjustments for layout rounding are incorrect at sufficiently high DPI.

The new algorithm produces results that meet the following criteria:A. The actual width assigned to a *-column is never less than its minimum width nor greater than its maximum width.B. Each -column that is not assigned its minimum or maximum width is assigned a width proportional to its -weight. To be precise, if two columns are declared with width x and y respectively, and if neither column receives its minimum or maximum width, the actual widths v and w assigned to the columns are in the same proportion: v / w == x / y.C. The total width allocated to “proportional” *-columns is equal to the space available after allocating to the constrained columns (fixed, auto, and *-columns that are allocated their min or max width). This might be zero, for instance if the sum of the minimum widths exceeds the Grid’s availbable width.D. All these statements are to be interpreted with respect to the “ideal” layout. When layout rounding is in effect, the actual widths can differ from the ideal widths by as much as one pixel.The old algorithm honored (A) but failed to honor the other criteria in the cases outlined above.Everything said about columns and widths in this article applies as well to rows and heights.

Suggestion By default, apps that target versions of the .NET Framework starting with the .NET Framework 4.7 will see the new algorithm, while apps that target the .NET Framework 4.6.2 or earlier versions will see the old algorithm.To override the default, use the following configuration setting:

<runtime>
<AppContextSwitchOverrides value="Switch.System.Windows.Controls.Grid.StarDefinitionsCanExceedAvailableSpace=true" />
</runtime>

The value ‘true’ selects the old algorithm, ‘false’ selects the new algorithm.

Scope Minor
Version ۴٫۷
Type Retargeting

WPF layout rounding of margins has changed

Details The way in which margins are rounded and borders and the background inside of them has changed. As a result of this change:

  • The width or height of elements may grow or shrink by at most one pixel.
  • The placement of an object can move by at most one pixel.
  • Centered elements can be vertically or horizontally off center by at most one pixel.

By default, this new layout is enabled only for apps that target the .NET Framework 4.6.

Suggestion Since this modification tends to eliminate clipping of the right or bottom of WPF controls at high DPIs, apps that target earlier versions of the .NET Framework but are running on the .NET Framework 4.6 can opt into this new behavior by adding the following line to the <runtime> section of the app.config file: <AppContextSwitchOverrides value="Switch.MS.Internal.DoNotApplyLayoutRoundingToMarginsAndBorderThickness=false" />Apps that target the .NET Framework 4.6 but want WPF controls to render using the previous layout algorithm can do so by adding the following line to the <runtime> section of the app.config file: <AppContextSwitchOverrides value="Switch.MS.Internal.DoNotApplyLayoutRoundingToMarginsAndBorderThickness=true" />.
Scope Minor
Version ۴٫۶
Type Retargeting

WPF Pointer-Based Touch Stack

Details This change adds the ability to enable an optional WM_POINTER based WPF touch/stylus stack. Developers that do not explicitly enable this should see no change in WPF touch/stylus behavior.Current Known Issues With optional WM_POINTER based touch/stylus stack:

  • No support for real-time inking.
  • While inking and StylusPlugins will still work, they will be processed on the UI Thread which can lead to poor performance.
  • Behavioral changes due to changes in promotion from touch/stylus events to mouse events
  • Manipulation may behave differently
  • Drag/Drop will not show appropriate feedback for touch input
  • This does not affect stylus input
  • Drag/Drop can no longer be initiated on touch/stylus events
  • This can potentially hang the application until mouse input is detected.
  • Instead, developers should initiate drag and drop from mouse events.
Suggestion Developers who wish to enable this stack can add/merge the following to their application’s App.config file:

<configuration>
<runtime>
<AppContextSwitchOverrides value="Switch.System.Windows.Input.Stylus.EnablePointerSupport=true"/>
</runtime>
</configuration>

Removing this or setting the value to false will turn this optional stack off.Please note that this stack is available only on Windows 10 Creators Update and above.

Scope Edge
Version ۴٫۷
Type Retargeting

WPF TextBox.Text can be out-of-sync with databinding

Details In some cases, the Text property reflects a previous value of the databound property value if the property is modified during a databinding write operation.
Suggestion This should have no negative impact. However, you can restore the previous behavior by setting the KeepTextBoxDisplaySynchronizedWithTextProperty property to false.
Scope Edge
Version ۴٫۵
Type Retargeting
Affected APIs

Windows Workflow Foundation (WF)

New (ambiguous) Dispatcher.Invoke overloads could result in different behavior

Details The .NET Framework 4.5 adds new overloads to Dispatcher.Invoke that include a parameter of type Action. When existing code is recompiled, compilers may resolve calls to Dispatcher.Invoke methods that have a Delegate parameter as calls to Dispatcher.Invoke methods with an Action parameter. If a call to a Dispatcher.Invoke overload with a Delegate parameter is resolved as a call to a Dispatcher.Invoke overload with an Action parameter, the following differences in behavior may occur:
Suggestion To avoid ambiguity (and potential differences in exception handling or blocking behaviors), code calling Dispatcher.Invoke can pass an empty object[] as a second parameter to the Invoke call to be sure of resolving to the .NET 4.0 method overload.
Scope Minor
Version ۴٫۵
Type Retargeting
Affected APIs

Some WorkFlow drag-and-drop APIs are obsolete

WorkFlow 3.0 types are obsolete

Details Windows Workflow Foundation (WWF) 3.0 APIs (those from the System.Workflow namespace) are now obsolete.
Suggestion New WWF 4.0 APIs (in System.Activities) should be used instead. An example of using the new APIs can be found here and further guidance is available here. Alternatively, since the WWF 3.0 APIs are still supported, they may be used and the build-time warning avoided either by suppressing it or by using an older compiler.
Scope Major
Version ۴٫۵
Type Retargeting

Workflow checksums changed from MD5 to SHA1

Details To support debugging with Visual Studio, the Workflow runtime generates a checksum for a workflow instance using a hashing algorithm. In the .NET Framework 4.6.2 and earlier versions, workflow checksum hashing used the MD5 algorithm, which caused issues on FIPS-enabled systems. Starting with the .NET Framework 4.7, the algorithm is SHA1. If your code has persisted these checksums, they will be incompatible.
Suggestion If your code is unable to load workflow instances due to a checksum failure, try setting the AppContext switch “Switch.System.Activities.UseMD5ForWFDebugger” to true.In code:

System.AppContext.SetSwitch("Switch.System.Activities.UseMD5ForWFDebugger", true);

Or in configuration:

<configuration>
<runtime>
<AppContextSwitchOverrides value="Switch.System.Activities.UseMD5ForWFDebugger=true" />
</runtime>
</configuration>
Scope Minor
Version ۴٫۷
Type Retargeting

XML, XSLT

XML schema validation is stricter

Details In the .NET Framework 4.5, XML schema validation is more strict. If you use xsd:anyURI to validate a URI such as a mailto protocol, validation fails if there are spaces in the URI. In previous versions of the .NET Framework, validation succeeded. The change affects only applications that target the .NET Framework 4.5.
Suggestion If looser .NET Framework 4.0 validation is needed, the validating application can target version 4.0 of the .NET Framework. When retargeting to .NET 4.5, however, code review should be done to be sure that invalid URIs (with spaces) are not expected as attribute values with the anyURI data type.
Scope Minor
Version ۴٫۵
Type Retargeting

XmlWriter throws on invalid surrogate pairs

Details For apps that target the .NET Framework 4.5.2 or previous versions, writing an invalid surrogate pair using exception fallback handling does not always throw an exception. For apps that target the .NET Framework 4.6, attempting to write an invalid surrogate pair throws an ArgumentException.
Suggestion If necessary, this break can be avoided by targeting the .NET Framework 4.5.2 or earlier. Alternatively, invalid surrogate pairs can be pre-processed into valid xml prior to writing them.
Scope Edge
Version ۴٫۶
Type Retargeting
Affected APIs

XSD Schema validation now correctly detects violations of unique constraints if compound keys are used and one key is empty

Details Versions of the .NET Framework prior to 4.6 had a bug that caused XSD validation to not detect unique constraints on compound keys if one of the keys was empty. In the .NET Framework 4.6, this issue is corrected. This will result in more correct validation, but it may also result in some XML not validating which previously would have.
Suggestion If looser .NET Framework 4.0 validation is needed, the validating application can target version 4.5 (or earlier) of the .NET Framework. When retargeting to .NET 4.6, however, code review should be done to be sure that duplicate compound keys (as described in this issue’s description) are not expected to validate.
Scope Edge
Version ۴٫۶
Type Retargeting

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