Question

我继承了一些通过WCF服务查询数据库的代码，然后在完成后使用回调。我正在尝试向该回调添加一些代码，以便在处理数据时更新UI。我发现在回调期间我无法更新UI：

client.GetDataAsync();
client.GetDataCompleted += new EventHandler<GetDataCompletedEventArgs>(GetDataCompleted);

void GetDataCompleted(object sender, GetDataCompletedEventArgs e)
{
  // Loop through the data
  // ...
  textBlock1.Text= "test1";
  Dispatcher.BeginInvoke(() => textBlock1.Text= "test2" );
  var thread = new Thread(() =>
  {
     // textBlock1.Text= "test3"; (this throws a cross-thread access exception)
     Dispatcher.BeginInvoke(() =>
     {
       textBlock1.Text= "test4";
     });
  }
  thread.Start();
  // ...
  Debug.WriteLine("done");
}

这些事情都没有更新UI，直到（显然）整个回调完成。这篇文章：

What thread calls the completed event handler on silverlight WCF calls?

建议回调在主UI线程上运行，以便不需要BeginInvoke调用。即使我在上面的代码中添加了各种延迟，它仍然无效。这可能吗？有更好的方法吗？

（这是对此的后续问题：Multiple asynchronous UI updates in Silverlight）

Answer 1

degorolls建议TPL正确，你的代码看起来如下（除了没有注释）（另外，必须在TPL中处理异常，所以这可能使它不值得，但我不认为它应该）。第一种方法将保持不变，并且基于事件的异步编程线程安全性得到处理（即：您总是返回到您调出的同一线程）我还注意到文本输出都是在做=而不是+ =，但这可能更像是输入溢出的问题因此，test1和test2将同时打印出来，但是从TPL代码吐出的所有东西都应该打印出来。 UI代码不应该做任何需要太多时间的事情，但是......只更新UI。那么，是否认为这是重构的一个重点？如果这有帮助，或者我错过了你想要的东西，请告诉我。

client.GetDataAsync();
client.GetDataCompleted += new EventHandler<GetDataCompletedEventArgs>(GetDataCompleted);

void GetDataCompleted(object sender, GetDataCompletedEventArgs e)
{
  // Loop through the data
  // ...
  textBlock1.Text= "test1";
  //////Dispatcher should not be needed here as this IS on the main UI thread
  Dispatcher.BeginInvoke(() => textBlock1.Text= "test2" );
  //////Everything that happens here should NOT be on the main UI thread, thus the cross-thread access exception
  //////You can do Dispatcher.CheckAccess to determine if you need to invoke or not
  //////Notice the newCopyOfDataToBeWritten. This is a closure, 
  //////so using the same referenced object will result in errant data as it loops
  //////Also, doing it this way does not guarantee any order that this will be written out
  //////This will utilize the parallel fully, but there are ways to force the order
  var task = Task.Factory.StartNew(()=>
    {
      Dispatcher.BeginInvoke(()=>textBlock1.Text += newCopyOfDataToBeWritten)
    }
  );
  // ...
  ///////I assume this is the end of the loop?
  Debug.WriteLine("done");
}

.... 以下基于您发布的内容的代码似乎对我有用

 var outsideThread = new Thread(()=>
 {         
     for(int i = 0; i < 20; i++)
          {
              //This code will show all at once since it is on the main thread, 
              //which is still running
              //If you want this to display one at a time also, then you need
              //to use threads and callbacks like below, also
              Dispatcher.BeginInvoke(()=>{textBlock1.Text += "outer" + i;});
              int newI = i;
              var thread = new Thread(() =>
              {
                  System.Threading.Thread.Sleep(1000 * newI);
                  Dispatcher.BeginInvoke(() =>
                  {
                      //This will display as it comes in

                      textBlock1.Text += "inner" + newI;
                  });
              });
              thread.Start();
          }
});
outsideThread.Start();

无法从异步方法完成回调更新Silverlight UI

1 个答案: