binding a command to a list - wpf

Question

I have the same command that I want to use for two controls on a dialog type window. As potentially interesting background, I'm using Josh Smith's ViewModel / RelayCommand ideas, since I am new to WPF and it's the first thing I've seen that I can actually understand from a big picture point of view.
So the command is a property of a ViewModel, and with the Button's built-in support, it is trivial and painless to bind to the command in the XAML:
<Button ... Command="{Binding Path=PickCommand}" Content="_Ok"></Button>
Now in a ListView, the only way I have gotten to use the same command hooked up to trigger on a double click is by using an event handler:
<ListView ...
ItemsSource="{Binding Path=AvailableProjects}"
SelectedItem="{Binding Path=SelectedProject, Mode=TwoWay}"
MouseDoubleClick="OnProjectListingMouseDoubleClick"
>
private void OnProjectListingMouseDoubleClick(object sender, MouseButtonEventArgs e) {
var vm = (ProjectSelectionViewModel) DataContext;
vm.Pick(); // execute the pick command
}
Is there a way to do this by binding the way the button does it?
Cheers,
Berryl
<------- implementation - is there a better way? --->
Your SelctionBehavior class was spot on, but I was confused at your xaml code. By setting the "Style" on the listViewItem I was getting the children of the DataContext where the command I want to execute lives. So I attached the behavior to the ListView itself:
<ListView ...Style="{StaticResource _attachedPickCommand}" >
And put the style in a resource dictionary:
<Style x:Key="_attachedPickCommand" TargetType="ListView">
<Setter Property="behaviors:SelectionBehavior.DoubleClickCommand" Value="{Binding Path=PickCommand}" />
</Style>
It works! But it 'feels' awkward setting the style property of the list view. Is this just because I am not comfortable with style as more than something visual in wpf or is there a better way to do this?
Cheers, and thanks!
Berryl

Answer 1

Yes there is! You can use attached behaviors and bind the command to that behavior.
public class SelectionBehavior {
public static readonly DependencyProperty CommandParameterProperty=
DependencyProperty.RegisterAttached("CommandParameter", typeof(object), typeof(SelectionBehavior));
public static readonly DependencyProperty DoubleClickCommandProperty=
DependencyProperty.RegisterAttached("DoubleClickCommand", typeof(ICommand), typeof(SelectionBehavior),
new PropertyMetadata(OnDoubleClickAttached));
private static void OnDoubleClickAttached(DependencyObject d, DependencyPropertyChangedEventArgs e) {
var fe=(FrameworkElement)d;
if(e.NewValue!=null && e.OldValue==null) {
fe.PreviewMouseDown+=fe_MouseDown;
} else if(e.NewValue==null && e.OldValue!=null) {
fe.PreviewMouseDown-=fe_MouseDown;
}
}
private static void fe_MouseDown(object sender, MouseButtonEventArgs e) {
if(e.ClickCount==2) {
var dep=(FrameworkElement)sender;
var command=GetDoubleClickCommand(dep);
if(command!=null) {
var param=GetCommandParameter(dep);
command.Execute(param);
}
}
}
public static ICommand GetDoubleClickCommand(FrameworkElement element) {
return (ICommand)element.GetValue(DoubleClickCommandProperty);
}
public static void SetDoubleClickCommand(FrameworkElement element, ICommand value) {
element.SetValue(DoubleClickCommandProperty, value);
}
public static object GetCommandParameter(DependencyObject element) {
return element.GetValue(CommandParameterProperty);
}
public static void SetCommandParameter(DependencyObject element, object value) {
element.SetValue(CommandParameterProperty, value);
}
}
and in the xaml you would need to set a style for a ListViewItem which represents your data in the ListView. Example
<ListView>
<ListView.ItemContainerStyle>
<Style TargetType="{x:Type ListViewItem}">
<Setter Property="local:SelectionBehavior.DoubleClickCommand" Value="{Binding Path=DataContext.PickCommand}"/>
<Setter Property="local:SelectionBehavior.CommandParameter" Value="{Binding Path=DataContext}"/>
</Style>
</ListView.ItemContainerStyle>
</ListView>
Here is some more information about the Attached Behavior pattern