Question

我正在尝试了解如何在使用async / await模式时从事件更新UI。下面是我在WinForm应用程序上使用的测试代码。我甚至不确定这是正确的方法。允许pwe_StatusUpdate方法更新UI的必要条件是什么？抛出跨线程操作错误。

感谢阅读。

 // calling code
    ProcessWithEvents pwe = new ProcessWithEvents();
    pwe.StatusUpdate += pwe_StatusUpdate;
    await pwe.Run();



 void pwe_StatusUpdate(string updateMsg)
    {
      // Error Here: Cross-thread operation not valid: Control '_listBox_Output' accessed from a thread other than the thread it was created on.
      _listBox_Output.Items.Add(updateMsg);
    }

-

// Class with long running process and event    
public delegate void StatusUpdateHandler(string updateMsg);

 public class ProcessWithEvents
  {
    public event StatusUpdateHandler StatusUpdate;

    public async Task Run()
    {
        await Task.Run(() =>
        {
            for (int i = 0; i < 10; i++)
                {

                    RaiseUpdateEvent(String.Format("Update {0}", i));

                    Thread.Sleep(500);
                }
            });

        }

        private void RaiseUpdateEvent(string msg)
        {
        if (StatusUpdate != null)
            StatusUpdate(msg);
        }
   }

-

Answer 1

The async pattern has support for progress updates

简而言之，您的async方法可以使用IProgress<T>，并且您的调用代码会传递该接口的实现（通常为Progress<T>）。

public class ProcessWithUpdates
{
  public async Task Run(IProgress<string> progress)
  {
    await Task.Run(() =>
    {
      for (int i = 0; i < 10; i++)
      {
        if (progress != null)
          progress.Report(String.Format("Update {0}", i));
        Thread.Sleep(500);
      }
    });
  }
}

// calling code
ProcessWithUpdates pwp = new ProcessWithUpdates();
await pwp.Run(new Progress<string>(pwp_StatusUpdate));

Answer 2

您应该使用Invoke的{{1}}方法。它在Control的线程中执行一些代码。您还可以检查Control属性以检查是否需要调用InvokeRequired方法（它检查调用方是否与创建控件的线程不同）。

简单示例：

Invoke

在某些情况下，您应该在调用void SomeAsyncMethod() { // Do some work if (this.InvokeRequired) { this.Invoke((MethodInvoker)(() => { DoUpdateUI(); } )); } else { DoUpdateUI(); } } void DoUpdateUI() { // Your UI update code here }方法之前检查IsHandleCreated的{{1}}属性。如果Control返回false，则需要等待创建Control的句柄

Answer 3

//只需声明一个像这样的委托

delegate void Add(string msg);

//然后声明委托方法，如下所示：

var add = new Add((msg) => {
   _listBox_Output.Items.Add(msg);
});

//现在只需调用委托：

void pwe_StatusUpdate(string updateMsg)
    {

      _listBox_Output.Invoke(add,updateMsg);
    }

Answer 4

这是另一个例子

async void DoExport()
{
    var rMsg = "";
    var t = await Task<bool>.Factory.StartNew(() => ExportAsMonthReport(LastMonth.Name, LastYear.Name, out rMsg));

    if (t)
    {
          BeginInvoke((Action)(() =>
          {
               spinnerMain.Visible = false;
               menuItemMonth.Enabled = true;

               MetroMessageBox.Show(this, rMsg, "Export", MessageBoxButtons.OK, MessageBoxIcon.Information, 200);
          }));
   }
   else
   {
          BeginInvoke((Action)(() =>
          {
               spinnerMain.Visible = false;
               menuItemMonth.Enabled = true;

               MetroMessageBox.Show(this, rMsg, "Export", MessageBoxButtons.OK, MessageBoxIcon.Error, 200);
          }));
    }
}

使用async await从事件更新UI

4 个答案: