在 windows 之间传递对象

Question

我试图将对象传递给下一个 window，但我收到了 Null 异常。所以在我的第一个 window:

        private void Button_Ok_Click(object sender, RoutedEventArgs e)
        {
           if (file == null)
           {
              System.Windows.MessageBox.Show("null");
              return;
           }
           MainWindow wnd = new MainWindow
           {
              myFileInfo = file
           };
           if(wnd.myFileInfo == null)
              System.Windows.MessageBox.Show("null2");
           wnd.Show();
        }

MessegeBox 未出现，因此 file 和 wnd.myFileInfo 绝对不为空。

第二个window:

    public partial class MainWindow : Window
    {
      public FileInfo myFileInfo;
      //...
      public MainWindow()
      {
          InitializeComponent();
          LabelFileName.Content = "File Name: " + this.myFileInfo.Name.ToString(); // Null exception
      //...
      }
    }

我竭尽全力寻找解决方案，不幸的是没有成功。

XAML:

<Grid>
    <Label Name="LabelFileName" Grid.Column="0" Grid.Row="0" />
</Grid>

异常消息：{"Object reference not set to an instance of an object."}

堆栈跟踪：

   at Charts.MainWindow..ctor() in c:\Users\Daniel\Documents\Visual Studio 2012\Projects\Charts\Charts\MainWindow.xaml.cs:line 143
   at Charts.Init.Button_Ok_Click(Object sender, RoutedEventArgs e) in c:\Users\Daniel\Documents\Visual Studio 2012\Projects\Charts\Charts\Init.xaml.cs:line 84
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
   at System.Windows.Controls.Primitives.ButtonBase.OnClick()
   at System.Windows.Controls.Button.OnClick()
   at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
   at System.Windows.UIElement.OnMouseLeftButtonUpThunk(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
   at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
   at System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
   at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
   at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
   at System.Windows.Input.InputManager.ProcessStagingArea()
   at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
   at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
   at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
   at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at System.Windows.Interop.HwndSource.InputFilterMessage(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, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   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.Dispatcher.Run()
   at System.Windows.Application.RunDispatcher(Object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run(Window window)
   at System.Windows.Application.Run()
   at Charts.App.Main() in c:\Users\Daniel\Documents\Visual Studio 2012\Projects\Charts\Charts\obj\Debug\App.g.cs:line 0
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

好的，我明白了为什么它会给我 null 异常。我尝试使用参数创建新的 window。第一个 MainWindow class 试图调用构造函数，在构造函数之后它将参数设置为对象。只要我在构造函数完成之前使用这个对象，它就会给我 null 异常。

Answer 1

如果您对名称进行 "ToString()"，这是否意味着 "Name" 的类型已经不是字符串？如果是这样的话，那么我想你应该给它一个值，或者至少实例化它？

第143行，是什么？

哎呀。在该行上放置一个断点，将鼠标悬停在每个对象和属性上并找出什么是 null。这让我很烦，我想知道！

Answer 2

你能不能为第二个 window 添加辅助构造函数？然后将对象传递给构造函数。

 public partial class MainWindow : Window
    {
      public FileInfo myFileInfo;
      //...
public MainWindow(FileInfo theInfo)
{
InitializeComponent();
myFileInfo = theInfo;
}

      public MainWindow()
      {
          InitializeComponent();
          LabelFileName.Content = "File Name: " + this.myFileInfo.Name.ToString(); // Null exception
      //...
      }
    }

然后在创建新的window时，传入文件信息对象。

Answer 3

您是否考虑过研究消息传递框架？例如 MVVMLight、Jounce 或任何其他 MVVM 框架中包含的框架？但是，推出您自己的事件聚合器并不困难。您必须有一种机制让 windows 都能获得事件聚合器的实例；通过某种服务定位器或依赖注入框架，甚至将其创建为属性主应用 class.

使用消息传递，您实际上是从第一个 window 发送一条消息，第二个 window 会收听它。

在您的场景中，单击按钮会显示 window，然后发布消息。第二个 window 收到消息后将能够根据其内容采取行动。

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