Command Behavior Attachments Arguments

Question

I have implemented the code in this article: http://wblo.gs/YvF. Everything works as expected but I don't know how to get access to the Arguments passed into the event handler when the event fires. I know there is the command parameter but how do I use it to get access to the EventArgs? Here is the code I have implemented...

DragEnter Class

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

public class DragEnter : Attachment<Control, DragEnterBehavior, DragEnter>
{
    private static readonly DependencyProperty behaviorProperty = Behavior();
    public static readonly DependencyProperty CommandProperty = Command(behaviorProperty);
    public static readonly DependencyProperty CommandParameterProperty = Parameter(behaviorProperty);

    public static void SetCommand(Control control, ICommand command) { control.SetValue(CommandProperty, command); }
    public static ICommand GetCommand(Control control) { return control.GetValue(CommandProperty) as ICommand; }
    public static void SetCommandParameter(Control control, object parameter) { control.SetValue(CommandParameterProperty, parameter); }
    public static object GetCommandParameter(Control buttonBase) { return buttonBase.GetValue(CommandParameterProperty); }
}

DragEnterBehavior Class

using System.Windows.Controls;
using Microsoft.Practices.Prism.Commands;

public class DragEnterBehavior : CommandBehaviorBase<Control>
{
    public DragEnterBehavior(Control selectableObject)
        : base(selectableObject)
    {
        selectableObject.DragEnter += (sender, args) => ExecuteCommand();
    }
}

The Implementation Code

public ICommand EditItemCommand
{
    get
    {
        if (editItemCommand == null)
            editItemCommand = new RelayCommand(param => EditItemControl(), pre => IsItemEditButtonEnabled());

        return editItemCommand;
    }
}

public void EditItemControl()
{
    ...
    ChangedView(itemEditorViewModel);
}

<ListBox Behaviors:DragEnter.Command="{Binding EditItemCommand}" ...

Any help on this would be appreciated. Thank You!

Answer 1

This is untested, but

• Change your DragEnterBehaviour to

  public class DragEnterBehavior : CommandBehaviorBase<Control>
  {
      public DragEnterBehavior(Control selectableObject)
          : base(selectableObject)
      {
          selectableObject.DragEnter += (sender, args) =>
                                        {
                                            CommandParameter = args;
                                            ExecuteCommand();
                                        };
      }
  } 
  

• Change your RelayCommand (I'm assuming this is from MVVM Light) to

  public ICommand EditItemCommand 
  { 
      get 
      { 
          if (editItemCommand == null) 
              editItemCommand = new RelayCommand<DragEventArgs>(
                  EditItemControl, IsItemEditButtonEnabled); 
  
          return editItemCommand; 
      } 
  } 
  
  public void EditItemControl(DragEventArgs args) 
  { 
      ... 
  } 
  

If you are using MVVM Light then you achieve the same result like this:

<i:Interaction.Triggers> 
    <i:EventTrigger EventName="DragEnter"> 
        <cmd:EventToCommand Command="{Binding DragEnterCommand}" 
            PassEventArgsToCommand="True" /> 
    </i:EventTrigger> 
</i:Interaction.Triggers>