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new-(ambiguous)-dispatcher_invoke-overloads-could-result-in-different-behavior.md

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

Scope

Minor

Version Introduced

4.5

Source Analyzer Status

Available

Change Description

The .NET Framework 4.5 adds new overloads to xref:System.Windows.Threading.Dispatcher.Invoke%2A?displayProperty=nameWithType that include a parameter of type xref:System.Action. When existing code is recompiled, compilers may resolve calls to Dispatcher.Invoke methods that have a xref:System.Delegate parameter as calls to Dispatcher.Invoke methods with an xref:System.Action parameter. If a call to a Dispatcher.Invoke overload with a xref:System.Delegate parameter is resolved as a call to a Dispatcher.Invoke overload with an xref:System.Action parameter, the following differences in behavior may occur:

  • If an exception occurs, the xref:System.Windows.Threading.Dispatcher.UnhandledExceptionFilter and xref:System.Windows.Threading.Dispatcher.UnhandledException events are not raised. Instead, exceptions are handled by the xref:System.Threading.Tasks.TaskScheduler.UnobservedTaskException?displayProperty=name event.

  • Calls to some members, such as xref:System.Windows.Threading.DispatcherOperation.Result, block until the operation has completed.

  • Quirked

  • Build-time break

Recommended Action

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 Framework 4.0 method overload.

Affected APIs

  • M:System.Windows.Threading.Dispatcher.Invoke(System.Delegate,System.Object[])
  • M:System.Windows.Threading.Dispatcher.Invoke(System.Delegate,System.TimeSpan,System.Object[])
  • M:System.Windows.Threading.Dispatcher.Invoke(System.Delegate,System.TimeSpan,System.Windows.Threading.DispatcherPriority,System.Object[])
  • M:System.Windows.Threading.Dispatcher.Invoke(System.Delegate,System.Windows.Threading.DispatcherPriority,System.Object[])

Category

Windows Workflow Foundation (WF)