Use of C # async and await

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Avoid Async Void

The Async method has three possible return types: task, task<t>, and void, but the intrinsic return type of the Async method is only task and task<t>. When converting from synchronous to asynchronous code, any method that returns a type T becomes an async method that returns task<t>, and any method that returns void becomes an Async method that returns a Task. The following code snippet shows a synchronous method that returns void and its equivalent async method:

Do synchronous work. Thread.Sleep (1000);}  //Do asynchronous work.  Await Task.delay (+);} 

The Async method that returns void has a specific purpose: to support asynchronous event handlers. event handlers can return some actual types but not work in the relevant language , it is very difficult to invoke an event handler for the return type, and the notion that the event handler actually returns some content is not significant. event handlers essentially return void, so the Async method returns void, So that you can use asynchronous event handlers. However, some semantics of the Async void method are related to async Task or async task<t The semantics of the > approach are slightly different.

The Async void method has different error handling semantics. When an async Task or Async task<t> method throws an exception, it catches the exception and places it on the Task object. for Async void methods, there is no Task object, so any exceptions thrown by the Async void method are raised directly on SynchronizationContext (active at the time the Async void method starts). Figure 2 demonstrates that the exception thrown from the Async void method cannot be captured in nature.

To create a truly asynchronous asynchronous function

As we mentioned earlier, the await statements await to the end inevitably call a really asynchronous asynchronous function that starts a new thread to do the actual work, so how do you define one of these functions yourself? In fact, it is very simple to use the task class to create such a function, the sample code is as follows:

        PrivateAsyncvoid Button_Click (Objectsender, RoutedEventArgs e) {resultstextbox.text + = String.Format ("\r\nmyasync ({0}). \ r \ n", Thread.CurrentThread.ManagedThreadId);while (True) Resultstextbox.text + = String.Format ("\r\nmyasync ({0}): {1}.\r\n", Thread.CurrentThread.ManagedThreadId,AwaitMyasync ()); }Public task<String> Myasync () { var t = new task<string> ((str) = = { var dt = DateTime.Now; Thread.Sleep (4000); return String.Format ("({0}) {1}-{2}", Thread.CurrentThread.ManagedThreadId, DT, DateTime.Now); }, null); T.start (); return t;}
The results of the operation are as follows:

Use of C # async and await