Question

There are two different ideas about the element which plays role of default command target in the “WPF Control Development” book:

Page 258» A command target is the object on which the command is
raised. ICommandSource interface contains a CommandTarget property
that can be set to a specific object. By default, the command source
itself is considered the command target.

Page 262» By default, when the CommandTarget is not set, the element
with the keyboard focus is used.

Furthermore, at this tutorial, we can leave menu items and buttons command target undefined while menu items only (i.e. and not buttons) can detect command target truly. So what’s the default command target?!

Answer 1

I think I just understood what this means:

If an element is focusable, it cannot detect undefined routed command
target automatically.

If an element is focusable, it means that it will always have keyboard focus when it is activated in order to raise a command. Thus, if it has a CommandBinding for the Command, it will always handle it itself, and if it hasn’t it will always be disabled.

However, you can get around this by setting FocusManager.IsFocusScope to true on the control’s container, like in this XAML:

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:my="clr-namespace:CommandRouting"
    Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="auto"/>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Menu IsMainMenu="True">
            <MenuItem x:Name="TestMenuItem" Command="{x:Static my:MainWindow.TestCommand}"/>
        </Menu>
        <GroupBox x:Name="CommandBindingOnControlsGroupBox" Header="CommandBinding on Controls" Grid.Row="1">
            <StackPanel>
            <Button x:Name="CommandBindingOnButtonButton" Command="{x:Static my:MainWindow.TestCommand}" Content="CommandBinding on Button">
               <Button.CommandBindings>
                    <CommandBinding Command="{x:Static my:MainWindow.TestCommand}" Executed="CommandBinding_Executed" PreviewExecuted="CommandBinding_Executed"/>
                </Button.CommandBindings>
            </Button>
                <TextBox x:Name="CommandBindingOnTextBoxTextBox">
                    <TextBox.CommandBindings>
                        <CommandBinding Command="{x:Static my:MainWindow.TestCommand}" Executed="CommandBinding_Executed"/>
                    </TextBox.CommandBindings>
                    <TextBox.InputBindings>
                        <!-- provide alternate keyboard shortcut -->
                        <KeyBinding Key="{x:Static Key.P}" Modifiers="{x:Static ModifierKeys.Control}" Command="{x:Static my:MainWindow.TestCommand}"/>
                    </TextBox.InputBindings>
                </TextBox>
                <Button x:Name="CommandTargetOnButtonButton" Command="{x:Static my:MainWindow.TestCommand}" Content="CommandTarget on Button" CommandTarget="{Binding ElementName=CommandBindingOnControlsGroupBox}">
                    <Button.CommandBindings>
                        <CommandBinding Command="{x:Static my:MainWindow.TestCommand}" Executed="CommandBinding_Executed"/>
                    </Button.CommandBindings>
                </Button>
            </StackPanel>
        </GroupBox>
        <GroupBox x:Name="CommandBindingOnContainerGroupBox" Header="CommandBinding on Container" Grid.Row="2">
            <GroupBox.CommandBindings>
                <CommandBinding Command="{x:Static my:MainWindow.TestCommand}" PreviewExecuted="CommandBinding_Executed"/>
            </GroupBox.CommandBindings>
            <StackPanel x:Name="CommandBindingOnInnerContainerStackPanel">
                <StackPanel.CommandBindings>
                    <CommandBinding Command="{x:Static my:MainWindow.TestCommand}" Executed="CommandBinding_Executed"/>
                </StackPanel.CommandBindings>
                <Button x:Name="CommandBindingOnContainerButton" Command="{x:Static my:MainWindow.TestCommand}" Content="CommandBinding on Two Containers">
                </Button>
                <TextBox x:Name="CommandBindingOnContainerTextBox">
                    <TextBox.InputBindings>
                        <!-- provide alternate keyboard shortcut -->
                        <KeyBinding Key="{x:Static Key.P}" Modifiers="{x:Static ModifierKeys.Control}" Command="{x:Static my:MainWindow.TestCommand}"/>
                    </TextBox.InputBindings>
                </TextBox>
            </StackPanel>
        </GroupBox>
        <GroupBox x:Name="OtherFocusScopeGroupBox" FocusManager.IsFocusScope="True" Header="Other FocusScope, No CommandBindings" Grid.Row="3">
            <StackPanel >
                <Button x:Name="OtherFocusScopeButton" Command="{x:Static my:MainWindow.TestCommand}" Content="Other FocusScope">
                </Button>
                <TextBox x:Name="OtherFocusScopeTextBox">
                    <TextBox.CommandBindings>
                        <CommandBinding Command="{x:Static my:MainWindow.TestCommand}" Executed="CommandBinding_Executed"/>
                    </TextBox.CommandBindings>
                    <TextBox.InputBindings>
                        <!-- provide alternate keyboard shortcut -->
                        <KeyBinding Key="{x:Static Key.P}" Modifiers="{x:Static ModifierKeys.Control}" Command="{x:Static my:MainWindow.TestCommand}"/>
                    </TextBox.InputBindings>
                </TextBox>
            </StackPanel>
        </GroupBox>
    </Grid>
</Window>