VB.NET WPF線程

Question

我對VB.NET和WPF比較陌生，我有一個基本的線程問題。

我只想弄清楚如何在使用NavigationService的頁面內使用Timer。以下是我有：

Public Class SplashPage 
    Inherits Page 

    Public Sub New(ByVal oData As Object) 

     StartTimer(5000) 

    End Sub 

    Public Sub StartTimer(ByVal iInterval As Double) 

     Dim timeoutTimer As New System.Timers.Timer 

     timeoutTimer.Interval = 5000 
     timeoutTimer.Enabled = True 

     'Function that gets called after each interval 
     AddHandler timeoutTimer.Elapsed, AddressOf OnTimedEvent 

    End Sub 

    Public Sub OnTimedEvent(source As Object, e As System.Timers.ElapsedEventArgs) 

     If NavigationService.CanGoBack Then 
      NavigationService.GoBack() 
     End If 

     'MessageBox.Show(e.SignalTime) 

    End Sub 

End Class 

的NavigationService.CanGoBack語句導致錯誤消息：「因爲不同的線程擁有它調用線程不能訪問此對象」

任何意見或建議，將不勝感激。謝謝！

• MG

Answer 1

這裏的問題是，你不能從後臺線程觸摸UI元素。在這種情況下，Timer.Elapsed事件在後臺線程中觸發，當您觸摸UI時會出錯。你需要觸摸元素

Private context = SynchronizationContext.Current 
Public Sub OnTimedEvent(source As Object, e As System.Timers.ElapsedEventArgs) 
    context.Post(AddressOf OnTimerInMainThread, e) 
End Sub 

Private Sub OnTimerInMainThread(state as Object) 
    Dim e = CType(state, ElapsedEventArgs) 
    If NavigationService.CanGoBack Then 
    NavigationService.GoBack() 
    End If 

    MessageBox.Show(e.SignalTime) 
End Sub