#1,090 – Sender vs. Source in CommandBinding Event Handlers

When handling a command’s Executed or CanExecute events, you can check the ExecutedRoutedEventArgs.Source or CanExecuteRoutedEventArgs.Source properties to get at the control that is the originator of the event.  But the event handler also includes a sender parameter that in many cases also points to the originator of the event.

The difference is:

• The Source property refers to the originator of the event
• The sender parameter refers to the object that owns the event handler

In the example below, clicking on the Button initiates a Paste command, which is bound to code using the parent Window’s CommandBindings property.

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Commands" Width="320" Height="220">

    <Window.CommandBindings>
        <CommandBinding Command="ApplicationCommands.Paste"
                        CanExecute="Paste_CanExecute"
                        Executed="Paste_Executed"/>
    </Window.CommandBindings>

    <StackPanel>
        <Button Content="Paste"
                Command="ApplicationCommands.Paste"
                Margin="10" Padding="10,3"
                HorizontalAlignment="Center" />
    </StackPanel>
</Window>

The Button is the Source of the routed command and the main Window is the sender.