Different Datacontext for Command and CommandParam

问题:

Is it possible to have a different Datacontext for a WPF Command and a CommandParameter?

<UserControl>
<UserControl.Resources>
    <viewmodels:ListViewGridBaseViewModel x:Key="vm" />
</UserControl.Resources>
<Grid>
    <ContentControl x:Name="currentContent" 
                    Content="{Binding Path=ListGrid}" >
        <ContentControl.ContextMenu>
            <ContextMenu >
                <MenuItem Command="{Binding Path=Save}" 
                          CommandParameter="{Binding ElementName=currentContent}"
                          DataContext="{StaticResource ResourceKey=vm}"
                          Header="Save">
                    <MenuItem.Icon>
                        <Image Source="{StaticResource ResourceKey=Save}"
                               Height="16"
                               Width="16"/>
                    </MenuItem.Icon>
                </MenuItem>
                <MenuItem Command="{Binding Path=Revert}" 
                          DataContext="{StaticResource ResourceKey=vm}"
                          Header="Revert">
                    <MenuItem.Icon>
                        <Image Source="{StaticResource ResourceKey=Revert}"
                               Height="16"
                               Width="16"/>
                    </MenuItem.Icon>
                </MenuItem>
            </ContextMenu>
        </ContentControl.ContextMenu>
    </ContentControl>
</Grid>
</UserControl>

I want the Binding for ListGrid bubbled up to another Viewmodel and the Command to a local ViewModel. But the CommandParameter should be the ContentControl. LOG is saying:

System.Windows.Data Error: 4 : Cannot find source for binding with 
reference 'ElementName=currentContent'. BindingExpression:(no path); 
DataItem=null; target element is 'MenuItem' (Name=''); 
target property is 'CommandParameter' (type 'Object')

回答1:

ContextMenu breaks the DataContext inheritance chain, that's why ElementName=currentContent cannot be found.

Look here for artificial inheritance context and use the class DataContextSpy

then do the following:

<UserControl>
<UserControl.Resources>
    <viewmodels:ListViewGridBaseViewModel x:Key="vm" />
    <local:DataContextSpy DataContext="{Binding ElementName=currentContent}" x:Key="Spy">
</UserControl.Resources>
<Grid>
    <ContentControl x:Name="currentContent" 
                    Content="{Binding Path=ListGrid}" >
        <ContentControl.ContextMenu>
            <ContextMenu >
                <MenuItem Command="{Binding Path=Save}" 
                          CommandParameter="{Binding DataContext,Source={StaticResource Spy}}"
                          DataContext="{StaticResource ResourceKey=vm}"
                          Header="Save">
                    <MenuItem.Icon>
                        <Image Source="{StaticResource ResourceKey=Save}"
                               Height="16"
                               Width="16"/>
                    </MenuItem.Icon>
                </MenuItem>
                <MenuItem Command="{Binding Path=Revert}" 
                          DataContext="{StaticResource ResourceKey=vm}"
                          Header="Revert">
                    <MenuItem.Icon>
                        <Image Source="{StaticResource ResourceKey=Revert}"
                               Height="16"
                               Width="16"/>
                    </MenuItem.Icon>
                </MenuItem>
            </ContextMenu>
        </ContentControl.ContextMenu>
    </ContentControl>
</Grid>
</UserControl>

回答2:

The ContextMenu has a separate VisualTree and is not part of UserControl's VisualTree and that's why Elementname binding's won't work. A simple workaround to use ElementName bindings is to add this in your UserControl's code-behind

NameScope.SetNameScope(currentContent, NameScope.GetNameScope(this)); 

Or you can use Enable ElementName Bindings with ElementSpy