AsyncCallback Delegate

Microsoft Silverlight will reach end of support after October 2021. Learn more.

References a method to be called when a corresponding asynchronous operation is completed.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)


<ComVisibleAttribute(True)> _
Public Delegate Sub AsyncCallback ( _
    ar As IAsyncResult _
public delegate void AsyncCallback(
    IAsyncResult ar



Use an AsyncCallback delegate to process the results of an asynchronous operation in a separate thread. The AsyncCallback delegate represents a callback method that is called when the asynchronous operation is completed. The callback method takes an IAsyncResult parameter, which is subsequently used to obtain the results of the asynchronous operation.

Platform Notes

Silverlight for Windows Phone Silverlight for Windows Phone

 Asynchronous delegate calls, specifically the BeginInvoke and EndInvoke methods, are not supported in Silverlight for Windows Phone. If you attempt to invoke delegates asynchronously, the application throws TargetInvocationException instead of NotSupportedException.

Version Information


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0


For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

See Also