更新UI异步？

Question

考虑这个例子：

Private Sub Button_Click(
    sender As Button, e As RoutedEventArgs) Handles btn.Click 

    sender.IsEnabled = False 

    Thread.Sleep(5000) 

    sender.IsEnabled = True 
End Sub 

我的方案的Button_Click是VM中的命令代表，以及Thread.Sleep是一些长期运行的进程（约2-10秒）。

我想，当用户调用该命令时，应立即更新禁用该按钮的UI，以便用户在运行时无法执行该操作，然后执行该操作，然后在操作完成时解除对按钮的阻止。

我试图包裹中间线如下所示：

Dispatcher.BeginInvoke(Sub() Thread.Sleep(5000)) 

但它并没有做的工作。
最好的办法是什么？

Answer 1

除了创建自己的线程外，还可以使用BackgroundWorker控件。 通过调用Method“RunWorkerAsync”，DoWork事件get在另一个线程中调用。

通过从您的UI线程调用方法“CancelAsync”，您可以将Backgroundworker设置为“Cancellation Pending”（控件的属性“CancellationPending”为true）。在长时间运行的后台线程中，您可以检查该属性（例如，如果您有循环：一旦CancellationPending为真，退出循环）。这是安全中止线程的一个很好的功能。

除了与BackgroundWorker的，你也可以报告线程的进展（如使用的进度）

例子：

Public Class Form1 

    Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles Me.Load 

     '** Set to true if you want the ReportProgress Event 
     BackgroundWorker1.WorkerReportsProgress = True 
     BackgroundWorker1.WorkerSupportsCancellation = True 
    End Sub 

    Private Sub BackgroundWorker1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork 

     Dim i As Integer 
     Dim n As Integer = 100 
     Dim iLastPerc As Integer 


     While Not BackgroundWorker1.CancellationPending AndAlso i < n 

     '** Do your time consuming actions here 
     Threading.Thread.Sleep(500) 

     If Math.Floor((i/n) * 100) > iLastPerc Then 
      '** If the Progress has changed. Report 
      iLastPerc = CInt(Math.Floor((i/n) * 100)) 
      BackgroundWorker1.ReportProgress(iLastPerc) 
     End If 

     i += 1 
     End While 

    End Sub 

    Private Sub btnStart_Click(sender As System.Object, e As System.EventArgs) Handles btnStart.Click 

     '** Run the Backgroundworker 
     BackgroundWorker1.RunWorkerAsync() 

    End Sub 

    Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged 

     '** Update the ProgressBar 
     ProgressBar1.Value = e.ProgressPercentage 

    End Sub 

    Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted 

     '** Worker is done. Check for Exceptions or evaluate the Result Object if you like 

    End Sub 

    Private Sub btnCancel_Click(sender As System.Object, e As System.EventArgs) Handles btnCancel.Click 

     '** Cancel the worker 
     BackgroundWorker1.CancelAsync() 

     MsgBox("Finished!") 

    End Sub 
End Class 

关于你问题的代码应该是：

Private Sub btn_Click(sender As Button, e As RoutedEventArgs) Handles btn.Click 
    sender.IsEnabled = False 
    Using bw As New BackgroundWorker() 
    AddHandler bw.DoWork, Sub(s, ea) Thread.Sleep(5000) 
    AddHandler bw.RunWorkerCompleted, Sub(s, ea) sender.IsEnabled = True 
    bw.RunWorkerAsync() 
    End Using 
End Sub 

Answer 2

将启用按钮的属性绑定到VM中的属性（比如ProcessComplete）。

使用按钮onclick事件触发虚拟机中启动漫长流程的方法。在进程运行时保持ProcessComplete False，然后在完成时将其设置为True。

Answer 3

按钮单击事件由UI线程处理，因此，当您调用thread.sleep时，您将使UI线程处于睡眠状态，并且在方法结束前您看不到任何更改。

因此，您需要在新线程上运行进程，并在进程结束时使用调度程序更改UI。

例如：

Private event TaskEnded() 
Private Sub Button_Click(sender As Button, e As RoutedEventArgs) Handles btn.Click 
    btn.IsEnabled = False 
    dim l as new Thread(sub() 
         Thread.Sleep(5000) 
         RaiseEvent TaskEnded 
         End Sub) 
    l.start() 
End Sub 

Private Sub bla() Handles Me.TaskEnded 
    dispatcher.BeginInvoke(sub() 
          btn.IsEnabled = True 
         end sub) 
End Sub 

的MVVM方式，您会在按钮IsEnabled属性为布尔属性绑定在你的视图模型，并直接更新VM欢迎使用属性，而不是上的按钮。