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MainWindow调用ImageViewModel中的操作。更多详情如下：

，调用MainWindow中的更改如下（MainWindow中的代码之后）：

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");
        }
    }

这是我的表现，但没有成功; ImageViewModel中的调用代码：

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());
        }
```

和例外：

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;知道如何让这个工作吗？非常感谢。

Answer 1

我敢打赌，在调用它时，你的DataContext为空的五块钱。这意味着它可能被称为太早。这可能意味着你应该在Dispatcher上推送你正在做的任何事情。

虽然您可能假设您的应用程序在调用此方法时已完全加载，但未必如此。要对此进行测试，请在调试期间设置断点并检查DataContext以查看它是否为空。

如果为null，则有两个选择。首先，回归。根据方法的调用方式，可以在加载期间多次调用。稍后的调用可能会显示非空的上下文。

另一个选项是在加载应用程序后使用Dispatcher稍后重新调用该方法。

这是一个看起来有点像C＃的伪代码，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);
}

线程调用主窗口？

1 个答案: