How to handle drag/drop without violating MVVM principals?

Question

Currently I have in my XAML

All of

Answer 1

Here is some code I wrote that allows you to drag and drop files onto a control without violating MVVM. It could easily be modified to pass the actual object instead of a file.

/// 

/// IFileDragDropTarget Interface
/// 
public interface IFileDragDropTarget
{
    void OnFileDrop(string[] filepaths);
}

/// 

/// FileDragDropHelper
/// 
public class FileDragDropHelper
{
    public static bool GetIsFileDragDropEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsFileDragDropEnabledProperty);
    }

    public static void SetIsFileDragDropEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsFileDragDropEnabledProperty, value);
    }

    public static bool GetFileDragDropTarget(DependencyObject obj)
    {
        return (bool)obj.GetValue(FileDragDropTargetProperty);
    }

    public static void SetFileDragDropTarget(DependencyObject obj, bool value)
    {
        obj.SetValue(FileDragDropTargetProperty, value);
    }

    public static readonly DependencyProperty IsFileDragDropEnabledProperty =
            DependencyProperty.RegisterAttached("IsFileDragDropEnabled", typeof(bool), typeof(FileDragDropHelper), new PropertyMetadata(OnFileDragDropEnabled));

    public static readonly DependencyProperty FileDragDropTargetProperty =
            DependencyProperty.RegisterAttached("FileDragDropTarget", typeof(object), typeof(FileDragDropHelper), null);

    private static void OnFileDragDropEnabled(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (e.NewValue == e.OldValue) return;
        var control = d as Control;
        if (control != null) control.Drop += OnDrop;
    }

    private static void OnDrop(object _sender, DragEventArgs _dragEventArgs)
    {
        DependencyObject d = _sender as DependencyObject;
        if (d == null) return;
        Object target = d.GetValue(FileDragDropTargetProperty);
        IFileDragDropTarget fileTarget = target as IFileDragDropTarget;
        if (fileTarget != null)
        {
            if (_dragEventArgs.Data.GetDataPresent(DataFormats.FileDrop))
            {
                fileTarget.OnFileDrop((string[])_dragEventArgs.Data.GetData(DataFormats.FileDrop));
            }
        }
        else
        {
            throw new Exception("FileDragDropTarget object must be of type IFileDragDropTarget");
        }
    }
}

Usage:

Ensure the DataContext inherits from IFileDragDropTarget and implements the OnFileDrop.

public class MyDataContext : ViewModelBase, IFileDragDropTarget
{
    public void OnFileDrop(string[] filepaths)
    {
        //handle file drop in data context
    }
}