Question

I have created a wpf application into which I have added a user control and a custom control. The custom control is used within the user control (planned to be used in many other Types of user controls).

For a quick example, the custom control has a dependency property of type Brush titled backgroundcolour, This is then set in the defualt template for the custom control as the background for the border. My thinking was that I would be able to set this value from the user control using the Command and CommandParameter properties. As i tried to do below

User Control xaml (TestControl is the custom control)

<Grid>
    <Grid.Resources>
        <MyNamespace:EditColourCommand x:Key="EditColour"/>
    </Grid.Resources>

    <Grid.ContextMenu>
        <ContextMenu>
            <MenuItem Name="Test" 
                      Header="Test" 
                      Command="{StaticResource EditColour}" 
                      CommandParameter="{Binding ElementName=testControl1, Path=BackgroundColour, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        </ContextMenu>
    </Grid.ContextMenu>

    <MyNamespace:TestControl HorizontalAlignment="Left" 
                             Margin="213,90,0,0" 
                             x:Name="testControl1" 
                             VerticalAlignment="Top" 
                             Height="77" 
                             Width="230"/>

</Grid>

My custom Control Code Behind:

public class TestControl : Control
{
    static TestControl()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(TestControl), 
            new FrameworkPropertyMetadata(typeof(TestControl)));
    }

    public static DependencyProperty BackgroundColourProperty = 
        DependencyProperty.Register("BackgroundColour", 
                                    typeof(Brush), 
                                    typeof(TestControl), 
                                    new PropertyMetadata(Brushes.Blue, 
                                        BackgroundColourPropertyChangedHandler));

    public Brush BackgroundColour
    {
        get
        {
            return (Brush)GetValue(BackgroundColourProperty);
        }
        set
        {
            SetValue(BackgroundColourProperty, value);
        }
    }

    public static void BackgroundColourPropertyChangedHandler(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
    } 
}

Finally, The Command

public class EditColourCommand : ICommand
{
    public bool CanExecute(object parameter)
    {
        return true;
    }

    public event EventHandler CanExecuteChanged;

    public void Execute(object parameter)
    {
        parameter = Brushes.Black;
    }
}

The command gets fired and it has the defualt value in this case blue as a parameter but it never sets the value to black. Can someone push me in the right direction please?

Answer 1

Just modify your Command to

CommandParameter="{Binding ElementName=testControl1}"

and modify your command execute to

public void Execute(object parameter)
{
    var ctrl = parameter as TestControl 
    ctrl.BackgroundColour = Brushes.Black;
}

you can’t expect the binding to work like you did in the CommandParameter.