线程调用主窗口？

Question

所以基本上我有一个MainWindow，一个类SetupViewModel在一个单独的cs文件中定义，另一个类ImageViewModel在一个单独的cs文件中； 我想知道无论如何我可以从ImageViewModel 调用MainWindow 中的操作。下面列出了更多详细信息：

• 在 ImageViewModel 中，调用 MainWindow 中的更改如下（遵循MainWindow 中的代码）：

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

• ViewType 变量在SetupViewModel 中定义如下

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

• 这是我的做法，但没有成功； ImageViewModel中的调用代码：

  试试 { 动作 SwitchTo2DView = delegate() { ((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());
          }
  

还有例外：

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 C# 的外行；知道我怎样才能完成这项工作吗？非常感谢。

Answer 1

我敢打赌，你的 DataContext 在被调用时是空的。这意味着它可能被调用得太早了。这可能意味着你应该把你正在做的任何事情都推到 Dispatcher 上。

虽然您可能假设在调用此方法时您的应用程序已完全加载，但这不一定是正确的。要对此进行测试，请在调试期间设置断点并检查 DataContext 是否为空。

如果它为空，您有两个选择。首先，只是返回。根据调用方法的方式，可能会在加载期间调用多次。稍后的调用可能会显示非空上下文。

另一种选择是使用Dispatcher 稍后在加载应用程序后重新调用该方法。

这里有一个小伪代码，看起来有点像 C#，甚至可以编译：

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);
}