How do I pass a specific viewmodel object in a button's CommandParam?

Question

I have a simple WPF program using the Master-Detail UI pattern, where the Detail shows the currently selected item of a collection in the Master pane. I'm using MVVM, and each XAML page is backed by a ViewModel object which is set as it's DataContext.

Now, I want to add a DELETE button in the Master pane to delete from the master list of items. However, I can't figure out how to pass the viewmodel object of the currently selected item as a button CommandParameter to the routed command handler code.

Thanks in advance for any pointers.

Mike

Answer 1

One option would be to create each command with a reference to the view model, and create a property on the view model which is bound to the currently selected item. This way you don't need to pass the selected item as a parameter - the command can retrieve it from the VM. If this isn't suitable for your circumstances, you could pass the selected item something like this:

<Button Content="Delete"
                Command="{Binding DeleteCommand}"
                CommandParameter="{Binding ElementName=listBox_, Path=SelectedValue}" />

Where listBox_ is a control which derives from Selector.

Hope that helps,

Paul

Answer 2

Something similiar to what Paul has shown is where your view model will know which item is currently selected. I.e.

public class MyVM
{
 public ObservableCollection<MyObject> MyCollection { get; set; }
 public MyObject CurrentItem { get; set; }
}

Your XAML can then be simply

CommandParameter="{Binding Path=CurrentItem}"

As long as your master pane sets the CurrentItem property when you select it, your command can simple have the CurrentItem set as the command parameter.