emby-toolbox/EmbyToolbox/Behaviors/FileDropBehavior.cs

using System.Windows;
using System.Windows.Input;
using EmbyToolbox.ViewModels;

namespace EmbyToolbox.Behaviors;

public static class FileDropBehavior
{
    public static readonly DependencyProperty DropCommandProperty =
        DependencyProperty.RegisterAttached(
            "DropCommand",
            typeof(RelayCommand),
            typeof(FileDropBehavior),
            new PropertyMetadata(null, OnDropCommandChanged));

    public static void SetDropCommand(DependencyObject element, RelayCommand? value)
    {
        element.SetValue(DropCommandProperty, value);
    }

    public static RelayCommand? GetDropCommand(DependencyObject element)
    {
        return (RelayCommand?)element.GetValue(DropCommandProperty);
    }

    private static void OnDropCommandChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is not UIElement element)
        {
            return;
        }

        element.AllowDrop = e.NewValue is not null;
        element.PreviewDragOver -= OnPreviewDragOver;
        element.Drop -= OnDrop;

        if (e.NewValue is not null)
        {
            element.PreviewDragOver += OnPreviewDragOver;
            element.Drop += OnDrop;
        }
    }

    private static void OnPreviewDragOver(object sender, DragEventArgs e)
    {
        if (e.Data.GetDataPresent(DataFormats.FileDrop))
        {
            e.Effects = DragDropEffects.Copy;
            e.Handled = true;
        }
    }

    private static void OnDrop(object sender, DragEventArgs e)
    {
        if (sender is not DependencyObject d)
        {
            return;
        }

        var command = GetDropCommand(d);
        if (command is null)
        {
            return;
        }

        if (e.Data.GetData(DataFormats.FileDrop) is string[] paths && command.CanExecute(paths))
        {
            command.Execute(paths);
            e.Handled = true;
        }
    }
}