This interface is used in asynchronous programming to act as a placeholder for the result of the async call. It is most commonly used when an instance of a delegate type is fired using the BeginInvoke method. (This idiom is used extensively throughout the .NET Framework Class Library.)

Asynchronous method calls can be harvested in a number of ways. A programmer can poll the call by checking the IsCompleted property of the IAsyncResult object to see if the call has completed yet. This, while perhaps the simplest approach, is also likely the most wasteful, as the caller needs to be in some sort of spin loop, repeatedly checking the property until a true is received.

A variant of the polling spin loop is to use the AsyncWaitHandle property of IAsyncResult. This is a standard Win32 handle that can be used in some of the synchronization primitives provided in the System.Threading namespace. Specifically, this property is a System.Threading.WaitHandle instance, meaning that the programmer can call any of the Wait methods: WaitOne( ), WaitAny( ), or WaitAll( ). The net effect is the same—put the calling thread to sleep until the async call completes.

Although not formally part of the IAsyncResult interface, a corresponding EndInvoke method is supported by delegates. The EndInvoke method blocks the calling thread until the async call completes. Alternatively, at the point of the async delegate call, a programmer can specify a callback delegate to call when the async call completes. This callback, a delegate instance of type AsyncCallback, is passed this IAsyncResult instance as part of the call. An optional generic argument can also be passed in as part of the async call, and this generic argument is available on the IAsyncResult through the AsyncState property. For an example of using IAsyncResult, see Section 16.3.

public interface IAsyncResult {
// Public Instance Properties
   public object AsyncState{get; }
   public WaitHandle AsyncWaitHandle{get; }
   public bool CompletedSynchronously{get; }
   public bool IsCompleted{get; }
}

Returned By

Multiple types

Passed To

Multiple types