c# - 使用异步等待从事件更新 UI

Question

我想了解如何在使用异步/等待模式时根据事件更新 UI。 下面是我在 WinForm 应用程序上使用的测试代码。我什至不确定这是正确的方法。允许 pwe_StatusUpdate 方法更新 UI 需要什么？那里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方法可以采用 IProgress<T> ，并且您的调用代码传入该接口(interface)的实现(通常是 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));