微软示例:
private async void StartButton_Click(object sender, RoutedEventArgs e) { // ExampleMethodAsync returns a Task<int>, which means that the method // eventually produces an int result. However, ExampleMethodAsync returns // the Task<int> value as soon as it reaches an await. ResultsTextBox.Text += " "; try { int length = await ExampleMethodAsync(); // Note that you could put "await ExampleMethodAsync()" in the next line where // "length" is, but due to when '+=' fetches the value of ResultsTextBox, you // would not see the global side effect of ExampleMethodAsync setting the text. ResultsTextBox.Text += String.Format("Length: {0} ", length); } catch (Exception) { // Process the exception if one occurs. } } public async Task<int> ExampleMethodAsync() { var httpClient = new HttpClient(); int exampleInt = (await httpClient.GetStringAsync("http://msdn.microsoft.com")).Length; ResultsTextBox.Text += "Preparing to finish ExampleMethodAsync. "; // After the following return statement, any method that's awaiting // ExampleMethodAsync (in this case, StartButton_Click) can get the // integer result. return exampleInt; } // Output: // Preparing to finish ExampleMethodAsync. // Length: 53292
上面是微软给的写法,给按钮的响应方法加上async,然后await ExampleMethodAsync
但是其实async和await表达式写法:
private async void button_Click(object sender, RoutedEventArgs e) { TB_Result.Text = await exampleAsync(); }
private async Task<string> exampleAsync() { return await Task.Run(() => { WebClient w = new WebClient(); w.DownloadFile("http://provissy.com", "webPage1"); w.DownloadFile("http://microsoft.com", "webPage2"); string a = w.DownloadString("http://microsoft.com"); return a; }); }
Task.Run 和 Lambda表达式,用起来其实更加简单。
在 => { }范围内写任何代码都是异步执行的,因此不用担心某几个语句是否会长时间堵住UI线程。
当然,你不能访问UI线程,否则会抛出异常。
要是访问UI线程,可以加上Dispacter.BeginInvoke();