#713 – 在拖拽操作中使用控件预览图作为鼠标(Setting the Cursor to an Image of an UIElement While Dragging)

原文地址：https://wpf.2000things.com/2012/12/17/713-setting-the-cursor-to-an-image-of-an-uielement-while-dragging/

在拖拽操作的过程中，你可以通过GiveFeedback 事件的处理函数来修改鼠标光标的样子。甚至可以将拖拽控件生成图片作为鼠标光标。

下面是根据Brandon Cannaday的代码 http://www.switchonthecode.com/tutorials/wpf-tutorial-how-to-use-custom-cursors 写的一个例子。他的代码有给鼠标帮助类，

public class CursorHelper{    private static class NativeMethods    {        public struct IconInfo        {            public bool fIcon;            public int xHotspot;            public int yHotspot;            public IntPtr hbmMask;            public IntPtr hbmColor;        }         [DllImport("user32.dll")]        public static extern SafeIconHandle CreateIconIndirect(ref IconInfo icon);         [DllImport("user32.dll")]        public static extern bool DestroyIcon(IntPtr hIcon);         [DllImport("user32.dll")]        [return: MarshalAs(UnmanagedType.Bool)]        public static extern bool GetIconInfo(IntPtr hIcon, ref IconInfo pIconInfo);    }     [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]    private class SafeIconHandle : SafeHandleZeroOrMinusOneIsInvalid    {        public SafeIconHandle()            : base(true)        {        }         override protected bool ReleaseHandle()        {            return NativeMethods.DestroyIcon(handle);        }    }     private static Cursor InternalCreateCursor(System.Drawing.Bitmap bmp)    {        var iconInfo = new NativeMethods.IconInfo();        NativeMethods.GetIconInfo(bmp.GetHicon(), ref iconInfo);         iconInfo.xHotspot = 0;        iconInfo.yHotspot = 0;        iconInfo.fIcon = false;         SafeIconHandle cursorHandle = NativeMethods.CreateIconIndirect(ref iconInfo);        return CursorInteropHelper.Create(cursorHandle);    }     public static Cursor CreateCursor(UIElement element)    {        element.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));        element.Arrange(new Rect(new Point(), element.DesiredSize));         RenderTargetBitmap rtb =          new RenderTargetBitmap(            (int)element.DesiredSize.Width,            (int)element.DesiredSize.Height,            96, 96, PixelFormats.Pbgra32);         rtb.Render(element);         var encoder = new PngBitmapEncoder();        encoder.Frames.Add(BitmapFrame.Create(rtb));         using (var ms = new MemoryStream())        {            encoder.Save(ms);            using (var bmp = new System.Drawing.Bitmap(ms))            {                return InternalCreateCursor(bmp);            }        }    }}

然后我们做一个简单的界面，将一个Label拖入另一个Label中，并且将Label作为鼠标。

<StackPanel Orientation="Vertical" HorizontalAlignment="Center" Margin="45">    <Label Content="Data to drag" Background="AliceBlue" Padding="15,10"           MouseLeftButtonDown="Label_MouseLeftButtonDown"           GiveFeedback="Label_GiveFeedback"/>    <Label Content="Drag to here" Background="MediumSpringGreen" Padding="15,10" Margin="20"           AllowDrop="True" Drop="Label_Drop"/></StackPanel>

下面是拖拽操作的代码，在GiveFeedback 事件处理函数中判断是否是Copy操作，如果是则改变鼠标。

private void Label_MouseLeftButtonDown(object sender, MouseButtonEventArgs e){    DataObject data = new DataObject(DataFormats.Text, ((Label)e.Source).Content);     DragDrop.DoDragDrop((DependencyObject)e.Source, data, DragDropEffects.Copy);} private void Label_Drop(object sender, DragEventArgs e){    ((Label)e.Source).Content = (string)e.Data.GetData(DataFormats.Text);} private Cursor customCursor = null; private void Label_GiveFeedback(object sender, GiveFeedbackEventArgs e){    if (e.Effects == DragDropEffects.Copy)    {        if (customCursor == null)            customCursor = CursorHelper.CreateCursor(e.Source as UIElement);         if (customCursor != null)        {            e.UseDefaultCursors = false;            Mouse.SetCursor(customCursor);        }    }    else        e.UseDefaultCursors = true;     e.Handled = true;}