CheckBox Command Behaviors for Silverlight MVVM Pattern
- by Blake Blackwell
I am trying to detect when an item is checked, and which item is checked in a ListBox using Silverlight 4 and the Prism framework. I found this example on creating behaviors, and tried to follow it but nothing is happening in the debugger. I have three questions:
Why isn't my command executing?
How do I determine which item was checked (i.e. pass a command parameter)?
How do I debug this? (i.e. where can I put break points to begin stepping into this)
Here is my code:
View:
<ListBox x:Name="MyListBox" ItemsSource="{Binding PanelItems, Mode=TwoWay}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<CheckBox IsChecked="{Binding Enabled}" my:Checked.Command="{Binding Check}" />
<TextBlock x:Name="DisplayName" Text="{Binding DisplayName}"/>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
ViewModel:
public MainPageViewModel()
{
_panelItems.Add( new PanelItem
{
Enabled = true,
DisplayName = "Test1"
} );
Check = new DelegateCommand<object>( itemChecked );
}
public void itemChecked( object o )
{
//do some stuff
}
public DelegateCommand<object> Check { get; set; }
Behavior Class
public class CheckedBehavior : CommandBehaviorBase<CheckBox>
{
public CheckedBehavior( CheckBox element )
: base( element )
{
element.Checked +=new RoutedEventHandler(element_Checked);
}
void element_Checked( object sender, RoutedEventArgs e )
{
base.ExecuteCommand();
}
}
Command Class
public static class Checked
{
public static ICommand GetCommand( DependencyObject obj )
{
return (ICommand) obj.GetValue( CommandProperty );
}
public static void SetCommand( DependencyObject obj, ICommand value )
{
obj.SetValue( CommandProperty, value );
}
public static readonly DependencyProperty CommandProperty =
DependencyProperty.RegisterAttached( "Command", typeof( CheckBox ), typeof( Checked ), new
PropertyMetadata( OnSetCommandCallback ) );
public static readonly DependencyProperty CheckedCommandBehaviorProperty =
DependencyProperty.RegisterAttached( "CheckedCommandBehavior", typeof( CheckedBehavior ), typeof( Checked ), null );
private static void OnSetCommandCallback( DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e )
{
CheckBox element = dependencyObject as CheckBox;
if( element != null )
{
CheckedBehavior behavior = GetOrCreateBehavior( element );
behavior.Command = e.NewValue as ICommand;
}
}
private static CheckedBehavior GetOrCreateBehavior( CheckBox element )
{
CheckedBehavior behavior = element.GetValue( CheckedCommandBehaviorProperty ) as CheckedBehavior;
if( behavior == null )
{
behavior = new CheckedBehavior( element );
element.SetValue( CheckedCommandBehaviorProperty, behavior );
}
return behavior;
}
public static CheckedBehavior GetCheckCommandBehavior( DependencyObject obj )
{
return (CheckedBehavior) obj.GetValue( CheckedCommandBehaviorProperty );
}
public static void SetCheckCommandBehavior( DependencyObject obj, CheckedBehavior value )
{
obj.SetValue( CheckedCommandBehaviorProperty, value );
}
}
I used this article to get me started, but I'll readily admit this is over my head.
