c# - WPF C# PreviewDrop/Drop 事件未触发(使用 dragadorner)

Question

我假设 previewdrop/drop 事件在检测到将元素作为放置目标的拖动目标时触发。在这种情况下，我的放置目标是一个文本框，我的拖动目标是一个标签。它们都是从 DB 动态创建的。我正在使用 DragAdorner 来克隆我正在拖动的元素，在实现 DragAdorner 之前，我的 DnD 运行良好，但在我使用 dragadorner 之后，它将无法工作。当我尝试调试时，我注意到我的 previewdrop 事件没有触发。

这是我的代码:

 tbox.Drop += new DragEventHandler(tbox_PreviewDrop); // text box , Drop Target
 tbox.DragOver += new DragEventHandler(tbox_DragOver);

Label lbl = new Label();  // Label , Drag Target 
             lbl.Content = s;
             lbl.Width = Double.NaN;
             lbl.Height = 40;
             lbl.FontSize = 19;
             lbl.PreviewMouseDown += new MouseButtonEventHandler(lbl_MouseDown);
             lbl.PreviewMouseMove += new MouseEventHandler(lbl_MouseMove);
            lbl.PreviewGiveFeedback += new GiveFeedbackEventHandler(lbl_GiveFeedback);


     private void lbl_MouseDown(object sender, MouseButtonEventArgs e)
    {
        startPoint = e.GetPosition(this);
      //  Mouse.OverrideCursor = Cursors.None;

    }

    private void lbl_MouseMove(object sender, MouseEventArgs e)
    {

        if (e.LeftButton == MouseButtonState.Pressed)
        {

          //  Mouse.OverrideCursor = Cursors.None;

            var source = sender as UIElement;
            Label lbl = sender as Label;
            Point current = e.GetPosition(this);
            Vector diff = startPoint - current;

            if (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
                Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance)
            {

                adorner = new DragAdorner(lbl, e.GetPosition(lbl));
                AdornerLayer.GetAdornerLayer(lbl).Add(adorner);

                var dragData = new DataObject(this);
                DragDrop.DoDragDrop(source, dragData, DragDropEffects.Copy);
                AdornerLayer.GetAdornerLayer(lbl).Remove(adorner);

            }
            startPoint = current;
        }
    }

    private void lbl_GiveFeedback(object sender, GiveFeedbackEventArgs e)
    {
        if (adorner != null)
        {
            Label lbl = sender as Label;
            var pos = lbl.PointFromScreen(GetMousePosition());
            adorner.UpdatePosition(pos);
            e.Handled = true;

        }
    }



private void tbox_PreviewDrop(object sender, DragEventArgs e)
        {

            (sender as TextBox).Text = string.Empty; // Empty the textbox from previous answer.
            (sender as TextBox).Background = Brushes.White;
            e.Effects = DragDropEffects.Move;
            e.Handled = true;

        }

        private void tbox_DragOver(object sender, DragEventArgs e)
        {
            e.Handled = true;
            e.Effects = DragDropEffects.Move;

        }
     [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    internal static extern bool GetCursorPos(ref Win32Point pt);

    [StructLayout(LayoutKind.Sequential)]
    internal struct Win32Point
    {
        public Int32 X;
        public Int32 Y;
    };

    public static Point GetMousePosition()
    {
        Win32Point w32Mouse = new Win32Point();
        GetCursorPos(ref w32Mouse);
        return new Point(w32Mouse.X, w32Mouse.Y);
    }

    private Point startPoint;
    private DragAdorner adorner;

装饰类文件:

 public class DragAdorner : Adorner {

public DragAdorner(UIElement adornedElement, Point offset)

    : base(adornedElement) {

    this.offset = offset;

    vbrush = new VisualBrush(AdornedElement);
    //vbrush.Opacity = .7;

}



public void UpdatePosition(Point location) {

    this.location = location;

    this.InvalidateVisual();

}



protected override void OnRender(DrawingContext dc) {

    var p = location;

    p.Offset(-offset.X, -offset.Y);

    dc.DrawRectangle(vbrush, null, new Rect(p, this.RenderSize));

}



private Brush vbrush;

private Point location;

private Point offset;

我看到了http://www.adorkable.us/books/wpf_control_development.pdf (第 103 页)但它对我来说太复杂了，因为我是个新手。

是因为我的GiveFeedBack事件和其他事件冲突了？

Answer 1

由于您的 DragAdorner 始终在您的光标下方，因此它将成为接收拖放的对象。如果您在 Adorner 的构造函数中设置 IsHitTestVisible = false;，它应该可以解决此问题。

即使您没有在 Adorner 上设置 AllowDrop，因为它在光标下，它会拦截放置尝试。但由于它不接受丢弃，它只会取消它。

更新

另一个问题是您将拖动操作中允许的效果设置为 DragDropEffects.Copy，但在 DragOver 和 Drop 中处理程序，您正在尝试执行 DragDropEffects.Move。这行不通，因为它们不是相同的操作。这些必须匹配。如果你想在拖动时启用这两种操作，你可以用按位或指定两者:

DragDrop.DoDragDrop(source, dragData, DragDropEffects.Copy | DragDropEffects.Move);

更新 2

如果你想将 string 以外的任何东西放到 TextBox 上，你必须使用 PreviewDrop 和 PreviewDragOver 事件。否则，TextBox 的默认处理将忽略任何其他内容。所以它看起来像这样:

tbox.PreviewDrop += new DragEventHandler(tbox_PreviewDrop); 
tbox.PreviewDragOver += new DragEventHandler(tbox_DragOver);