Dispatcher.Invoke and Dispatcher.BeginInvoke

Dispatcher.Invoke是同步执行，msdn描述：

Executes the specified delegate with the specified arguments synchronously on the thread the Dispatcher is associated with.

返回值是object， 是被调用的委托的返回值，如果该委托没有返回值，则为null。它有好几个重载方法，下面是其中之一：

public Object Invoke(
	Delegate method,
	paramsObject[] args
)

Invoke is a synchronous operation; therefore, control will not return to the calling object until after the callback returns.

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Dispatcher.BeginInvoke是异步执行，msdn描述：

Executes the specified delegate asynchronously with the specified arguments on the thread that the Dispatcher was created on.

返回值是DispatcherOperation, An object, which is returned immediately after BeginInvoke is called, that can be used to interact with the

delegate as it is pending execution in the event queue. 它有好几个重载方法，下面是其中之一：

public DispatcherOperation BeginInvoke(
	Delegate method,
	params Object[] args
)

不同点是Dispatcher.Invoke直到回调返回之后才将控制权返回给调用对象。Dispatcher.BeginInvoke是立即返回控制权给调用对象，只是把delegate加到消息循环中。

 

如下面的例子：

 

private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            Test1();
            Test2();
            Test3();
        }

        private void Test1()
        {
            // 同步的按代码顺序执行
            Dispatcher.Invoke(new Action<string>(Console.WriteLine), System.Windows.Threading.DispatcherPriority.SystemIdle, "Invoke 1");
            Dispatcher.Invoke(new Action<string>(Console.WriteLine), System.Windows.Threading.DispatcherPriority.Send, "Invoke 2");
            // 以下3个异步，
            Dispatcher.BeginInvoke(new Action<string>(Console.WriteLine), System.Windows.Threading.DispatcherPriority.Normal, "BeginInvoke 1");
            Dispatcher.BeginInvoke(new Action<string>(Console.WriteLine), System.Windows.Threading.DispatcherPriority.Send, "BeginInvoke 2");
            // 异步默认的DispatcherPriority是Normal
            DispatcherOperation dop = Dispatcher.BeginInvoke(new Action<string>(Console.WriteLine), "BeginInvoke 3");
            Console.WriteLine("dop.Priorty: " + dop.Priority.ToString());

            Console.WriteLine("Hello normal");
        }

        private void Test2()
        {
            Dispatcher.BeginInvoke(new Action(() => MessageBox.Show("Invoke 1: Hello world")));
            MessageBox.Show("Invoke 2: Hello world");
        }

        private void Test3()
        {
            Dispatcher.BeginInvoke(new Action(() => { MessageBox.Show("hello 1"); }), System.Windows.Threading.DispatcherPriority.Background);
            MessageBox.Show("hello 2");
        }

输出结果：

Invoke 1
 Invoke 2
 dop.Priorty: Normal
 Hello normal
 BeginInvoke 2
 BeginInvoke 1
 BeginInvoke 3