using System.Windows;

using Microsoft.Xaml.Behaviors;

/// <summary>
/// 拖拽文件事件
/// </summary>
/// <example>DropFileBehaviors Data="{Binding FileNames,Mode=OneWayToSource}"从依赖属性传到源属性，通过源属性实现Mvvm</example>
/// <remarks>设置窗口属性AllowDrop，在上层覆盖一个面板如Grid，设置窗口的DropEnter和DropLeave(EventTrigger)事件，控制其显隐以及控制Drop事件后隐藏(ChangePropertyAction)</remarks>
class DropFileBehavior : Behavior<FrameworkElement>
{
    public string[] Data
    {
        get { return (string[])GetValue(DataProperty); }
        set { SetValue(DataProperty, value); }
    }

    public static readonly DependencyProperty DataProperty =
        DependencyProperty.Register(nameof(Data), typeof(string[]), typeof(DropFileBehavior), new PropertyMetadata(null));


    protected override void OnAttached()
    {
        AssociatedObject.AllowDrop = true;
        AssociatedObject.Drop += DropHandler;
    }

    private void DropHandler(object sender, DragEventArgs e)
    {
        if (e.Data.GetDataPresent(DataFormats.FileDrop))
        {
            Data = (string[])e.Data.GetData(DataFormats.FileDrop);
        }
    }

    protected override void OnDetaching()
    {
        AssociatedObject.Drop -= DropHandler;
    }
    protected override void OnChanged()
    {
        base.OnChanged();
    }
}