在 WPF 应用程序中，有一个 Grid 包含许多对象(它们派生自自定义控件).我想使用上下文菜单对它们中的每一个执行一些操作:
<Grid.ContextMenu><上下文菜单><MenuItem Name="EditStatusCm" Header="更改状态" Click="EditStatusCm_Click"/></上下文菜单></Grid.ContextMenu>但在事件处理程序中，我无法知道右键单击了哪些对象:
private void EditStatusCm_Click(object sender, RoutedEventArgs e){MyCustControl SCurrent = new MyCustControl();MenuItem menu = 作为 MenuItem 的发件人；SCurrent = menu.DataContext as MyCustControl;//这里我得到一个运行时错误SCurrent.Status = MyCustControl.Status.Sixth;}在注释行上，调试器说:对象引用未设置为对象的实例.
请帮忙，我的代码有什么问题?
已编辑(添加):
我尝试做同样的事情，使用 Command 方法:
我用 RoutedUICommand Requery 声明了一个 DataCommands 类，然后使用了 Window.CommandBindings
<Window.CommandBindings><CommandBinding Command="MyNamespace:DataCommands.Requery" Executed="RequeryCommand_Executed"></CommandBinding></Window.CommandBindings>MenuItem 的 XAML 现在看起来像:
<Grid.ContextMenu><上下文菜单><MenuItem Name="EditStatusCm" Header="更改状态" Command="MyNamespace:DataCommands.Requery"/></上下文菜单></Grid.ContextMenu>事件处理程序看起来像:
private void RequeryCommand_Executed(object sender, ExecutedRoutedEventArgs e){IInputElement parent = (IInputElement)LogicalTreeHelper.GetParent((DependencyObject)sender);MyCustControl SCurrent = new MyCustControl();SCurrent = (MuCustControl) 父级；string str = SCurrent.Name.ToString();//这里我得到同样的错误消息框.Show(str);}但调试器显示相同的运行时错误:对象引用未设置为对象的实例.
我的两种方法都缺少什么?
我应该如何在 WPF 上下文菜单项单击事件处理程序中引用右键单击的对象?
注意CommandParameter
<网格背景=红色"高度=100"宽度=100"><Grid.ContextMenu><上下文菜单><菜单项标头="更改状态"点击="EditStatusCm_Click"CommandParameter="{Binding RelativeSource={RelativeSource Self}, Path=Parent}"/></上下文菜单></Grid.ContextMenu></网格>并在处理程序中使用它来确定它是哪个网格
private void EditStatusCm_Click(object sender, RoutedEventArgs e){MenuItem mi = 作为 MenuItem 的发件人；如果(mi！= null){ContextMenu cm = mi.CommandParameter as ContextMenu;如果(厘米！= 空){网格 g = cm.PlacementTarget 作为网格；如果 (g != null){Console.WriteLine(g.Background);//将打印红色}}}}更新:
如果您希望 menuitem 处理程序访问 Grid 的子项而不是 Grid 本身，请使用此方法
<网格背景=红色"高度=100"宽度=100"><网格.资源><ContextMenu x:Key="TextBlockContextMenu"><菜单项标头="更改状态"点击="EditStatusCm_Click"CommandParameter="{Binding RelativeSource={RelativeSource Self}, Path=Parent}"/></上下文菜单><Style TargetType="{x:Type TextBlock}"><Setter Property="ContextMenu" Value="{StaticResource TextBlockContextMenu}"/></风格></Grid.Resources><Grid.RowDefinitions><行定义/><行定义/></Grid.RowDefinitions><TextBlock 文本="Row0" Grid.Row="0"/><TextBlock 文本="Row1" Grid.Row="1"/></网格>只需将 TextBlocks 替换为您的自定义对象类型即可.然后在事件处理程序中，将 Grid g = cm.PlacementTarget as Grid 替换为 TextBlock t = cm.PlacementTarget as TextBlock(或任何您的自定义对象类型).p>
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>
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;
}
On that commented line Debugger says: Object reference not set to an instance of an object.
Please help, what is wrong in my code?
Edited (added):
I tried to do the same, using Command approach:
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>
XAML of MenuItem now looks like:
<Grid.ContextMenu>
<ContextMenu>
<MenuItem Name="EditStatusCm" Header="Change status" Command="MyNamespace:DataCommands.Requery"/>
</ContextMenu>
</Grid.ContextMenu>
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);
}
But debugger shows the same run-time error: Object reference not set to an instance of an object.
What is missing in my both approaches?
How I should reference right-clicked object in WPF Context Menu item click event handler?
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>
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
}
}
}
}
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>
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).
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