線程調用主窗口？

Question

所以基本上我有一個MainWindow，一個類別SetupViewModel在一個單獨的cs文件中定義，另一個類ImageViewModel在一個單獨的cs文件中; 我想知道有無論如何我可以從ImageViewModel調用MainWindow的操作。詳情如下：

• 在ImageViewModel

  ，調用在主窗口的變化如下（在MainWindow以下代碼）：

  this.Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Normal, 
         new Action(
          delegate() 
          { 
            ((SetupViewModel)this.DataContext).ViewType = Convert.ToInt32(ViewTypes.ViewType2D); 
          } 
         ) 
        ); 
  

• 的ViewType變量在SetupViewModel定義如下

  private int _viewType; 
      public int ViewType 
      { 
       get 
       { 
        return _viewType; 
       } 
       set 
       { 
        _viewType = value; 
        OnPropertyChanged("ViewType"); 
       } 
      } 
  

• 這是我做過的，但沒有成功;在ImageViewModel的invoke代碼：

  嘗試 { 行動SwitchTo2DView =委託（） { （（CaptureSetupViewModel）System.Windows.Application.Current.MainWindow.DataContext）.ViewType = Convert.ToInt32（ViewTypes.ViewType2D） ; };

    System.Windows.Application.Current.MainWindow.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Normal, SwitchTo2DView); 
       } 
       catch (Exception ex) 
       { 
        Console.WriteLine("Caught exception: " + ex.ToString()); 
       } 
  

和異常：

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object. 
    at CaptureSetupDll.ViewModel.LiveImageViewModel.<StartZStackPreview>b__2c() 
    --- End of inner exception stack trace --- 
    at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) 
    at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) 
    at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) 
    at System.Delegate.DynamicInvokeImpl(Object[] args) 
    at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter) 
    at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) 
    at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) 
    at System.Windows.Threading.DispatcherOperation.InvokeImpl() 
    at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state) 
    at System.Threading.ExecutionContext.runTryCode(Object userData) 
    at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) 
    at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) 
    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) 
    at System.Windows.Threading.DispatcherOperation.Invoke() 
    at System.Windows.Threading.Dispatcher.ProcessQueue() 
    at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) 
    at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) 
    at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) 
    at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter) 
    at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) 
    at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) 
    at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Boolean isSingleParameter) 
    at System.Windows.Threading.Dispatcher.Invoke(DispatcherPriority priority, Delegate method, Object arg) 
    at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) 
    at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) 
    at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) 
    at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) 
    at System.Windows.Threading.DispatcherOperation.Wait(TimeSpan timeout) 
    at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Boolean isSingleParameter) 
    at System.Windows.Threading.Dispatcher.Invoke(DispatcherPriority priority, Delegate method) 
    at CaptureSetupDll.ViewModel.LiveImageViewModel.StartZStackPreview() 

我是外行到C＃;任何想法我如何能做到這一點？非常感謝。

Answer 1

我打賭你五個錢，你的DataContext在調用時是空的。這意味着它可能被稱爲太早。這可能意味着你應該推動你在Dispatcher上做的任何事情。

雖然你可能假設你的應用程序在調用這個方法時被完全加載，但它不一定是真的。要測試這個，在調試過程中設置一個斷點並檢查DataContext以查看它是否爲空。

如果它爲空，則有兩種選擇。首先，回來。根據調用方法的不同，可能會在加載過程中多次調用該方法。稍後的調用可能會顯示非空的上下文。

另一種選擇是在加載應用程序後，使用Dispatcher稍後重新調用該方法。

這裏有一個小的僞代碼看起來有點像C＃，甚至可能編譯：

public void CheckTheDataContext() 
{ 
    // is it null? 
    if(this.DataContext == null) 
    { 
     // then drop an Action re-invoking this method later 
     // when the application idles out a bit 
     Dispatcher.BeginInvoke((Action)(() => 
     { 
      CheckTheDataContext(); 
     }), System.Windows.Threading.DispatcherPriority.ApplicationIdle); 
     return; 
    } 
    DoSomethingElseWithTheContext(DataContext); 
}