如何引用WPF上下文菜单右键点击的对象单击事件处理程序？ [英] How to reference right-clicked object in WPF Context Menu item click event handler?

问题描述

在WPF应用程序有一个电网与多个对象（它们是从一个自定义控件派生）。我想在他们每个人的使用右键菜单中执行某些操作：

In WPF application there is a Grid with a number of objects (they are derived from a custom control). I want to perform some actions on each of them using context menu:

   <Grid.ContextMenu>
     <ContextMenu>
       <MenuItem  Name="EditStatusCm" Header="Change status" Click="EditStatusCm_Click"/>
     </ContextMenu>                   
   </Grid.ContextMenu> 

不过，在事件处理程序我不能知道哪些对象是右键单击：

But in the event handler I cannot get know which of the objects was right-clicked:

    private void EditStatusCm_Click(object sender, RoutedEventArgs e)
    {
        MyCustControl SCurrent = new MyCustControl();
        MenuItem menu = sender as MenuItem;
        SCurrent = menu.DataContext as MyCustControl; // here I get a run-time error
        SCurrent.Status = MyCustControl.Status.Sixth;
    }

在该注释行调试器说：的未将对象引用设置到对象的实例。的

On that commented line Debugger says: Object reference not set to an instance of an object.

请帮忙，什么是错在我的代码？

Please help, what is wrong in my code?

编辑（添加）：

我试图做同样的，使用的命令办法

I tried to do the same, using Command approach:

我声明了一个 DataCommands 类具有 RoutedUICommand重新查询然后用 Window.CommandBindings

I declared a DataCommands Class with RoutedUICommand Requery and then used Window.CommandBindings

<Window.CommandBindings>
  <CommandBinding Command="MyNamespace:DataCommands.Requery" Executed="RequeryCommand_Executed"></CommandBinding>
</Window.CommandBindings>

菜单项的XAML现在看起来像：

XAML of MenuItem now looks like:

<Grid.ContextMenu>
 <ContextMenu>
  <MenuItem  Name="EditStatusCm" Header="Change status"  Command="MyNamespace:DataCommands.Requery"/>
 </ContextMenu>                   
</Grid.ContextMenu>

和事件处理程序是这样的：

And event handler looks like:

    private void RequeryCommand_Executed(object sender, ExecutedRoutedEventArgs e)
    {
        IInputElement parent = (IInputElement)LogicalTreeHelper.GetParent((DependencyObject)sender);
        MyCustControl SCurrent = new MyCustControl();
        SCurrent = (MuCustControl)parent;
        string str = SCurrent.Name.ToString();// here I get the same error
        MessageBox.Show(str);
    }

但调试器显示相同的运行时错误： 对象引用未设置到对象的实例。的

But debugger shows the same run-time error: Object reference not set to an instance of an object.

什么在我的这两种方法丢失？

What is missing in my both approaches?

我应该如何引用WPF上下文菜单项Click事件处理程序右键点击的对象？

How I should reference right-clicked object in WPF Context Menu item click event handler?

推荐答案

请注意在CommandParameter

note the CommandParameter

<Grid Background="Red" Height="100" Width="100">
    <Grid.ContextMenu>
        <ContextMenu>
            <MenuItem 
                Header="Change status" 
                Click="EditStatusCm_Click"
                CommandParameter="{Binding RelativeSource={RelativeSource Self}, Path=Parent}" />
        </ContextMenu>
    </Grid.ContextMenu>
</Grid>

和在处理程序使用它来找出哪些网格是

and use it in the handler to figure out which Grid it is

    private void EditStatusCm_Click(object sender, RoutedEventArgs e)
    {
        MenuItem mi = sender as MenuItem;
        if (mi != null)
        {
            ContextMenu cm = mi.CommandParameter as ContextMenu;
            if (cm != null)
            {
                Grid g = cm.PlacementTarget as Grid;
                if (g != null)
                {
                    Console.WriteLine(g.Background); // Will print red
                }
            }
        }
    }

更新：的结果
如果你想在菜单项处理程序来获取到网格的孩子而网格本身，使用这种方法。

Update:
If you want the menuitem handler to get to the Grid's children instead of the Grid itself, use this approach

<Grid Background="Red" Height="100" Width="100">
    <Grid.Resources>
        <ContextMenu x:Key="TextBlockContextMenu">
            <MenuItem 
                Header="Change status" 
                Click="EditStatusCm_Click"
                CommandParameter="{Binding RelativeSource={RelativeSource Self}, Path=Parent}" />
        </ContextMenu>

        <Style TargetType="{x:Type TextBlock}">
            <Setter Property="ContextMenu" Value="{StaticResource TextBlockContextMenu}" />
        </Style>
    </Grid.Resources>

    <Grid.RowDefinitions>
        <RowDefinition />
        <RowDefinition />
    </Grid.RowDefinitions>

    <TextBlock Text="Row0" Grid.Row="0" />
    <TextBlock Text="Row1" Grid.Row="1" />
</Grid>

只需要用无论您的自定义对象类型是的TextBlocks。然后在事件处理程序，替换电网G = cm.PlacementTarget为网格与 TextBlock的T = cm.PlacementTarget作为TextBlock的 （或任何你自定义的对象类型）。

Just replace the TextBlocks with whatever your custom object type is. Then in the event handler, replace Grid g = cm.PlacementTarget as Grid with TextBlock t = cm.PlacementTarget as TextBlock (or whatever your custom object type is).

这篇关于如何引用WPF上下文菜单右键点击的对象单击事件处理程序？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！