我假设 previewdrop/drop 事件在检测到一个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，在实施 DragAdorner 之前，我的 DnD 工作得很好，但在我使用 dragadorner 之后，它就不起作用了。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;
和装饰类文件：
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;
}
我看过http://www.adorkable.us/books/wpf_control_development.pdf（第 103 页），但对我来说太复杂了，因为我是新手。
是因为我的 GiveFeedBack 事件与其他事件发生冲突吗？