#714 – Setting the Cursor to Render Some Text While Dragging

You can use the GiveFeedback to change the cursor during a drag-and-drop operation.  You can set the cursor to be some text by rendering a visual element to a bitmap and then converting that bitmap to a cursor.

Here’s a helper class containing a method that converts some text to a cursor.

    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(string cursorText)
        {
            // Text to render
            FormattedText fmtText = new FormattedText(cursorText,
                    new CultureInfo("en-us"),
                    FlowDirection.LeftToRight,
                    new Typeface(new FontFamily("Arial"), FontStyles.Normal, FontWeights.Normal, new FontStretch()),
                    12.0,  // FontSize
                    Brushes.Black);

            // The Visual to use as the source of the RenderTargetBitmap.
            DrawingVisual drawingVisual = new DrawingVisual();
            DrawingContext drawingContext = drawingVisual.RenderOpen();
            drawingContext.DrawText(fmtText, new Point());
            drawingContext.Close();

            // The BitmapSource that is rendered with a Visual.
            RenderTargetBitmap rtb = new RenderTargetBitmap(
                (int)drawingVisual.ContentBounds.Width,
                (int)drawingVisual.ContentBounds.Height,
                96,   // dpiX
                96,   // dpiY
                PixelFormats.Pbgra32);
            rtb.Render(drawingVisual);

            // Encoding the RenderBitmapTarget into a bitmap (as PNG)
            PngBitmapEncoder 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);
                }
            }
        }
    }

We can test this code by setting the cursor to some text when we drag a Label.

    <StackPanel>
        <Label Content="Mayflower" Background="AliceBlue" 
               HorizontalAlignment="Center" Margin="15" Padding="20,5"
               MouseLeftButtonDown="Label_MouseLeftButtonDown"
               GiveFeedback="Label_GiveFeedback"/>
        <Label Content="Drag to here" Background="SpringGreen" 
               HorizontalAlignment="Center" Margin="15"
               Drop="Label_Drop"/>
    </StackPanel>

Here’s the code for the drag-and-drop operation.

        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("Mayflower - 18 Dec 1620");

                if (customCursor != null)
                {
                    e.UseDefaultCursors = false;
                    Mouse.SetCursor(customCursor);
                }
            }
            else
                e.UseDefaultCursors = true;

            e.Handled = true;
        }

714-001

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About Sean
Software developer in the Twin Cities area, passionate about software development and sailing.

3 Responses to #714 – Setting the Cursor to Render Some Text While Dragging

  1. Pingback: Setting the Cursor to Render Some Text While Dragging in WPF | Around computing

  2. Miguel de Campos says:

    Hi Sean,

    Thanks for your incredibly useful blog.

    InternalCreateCursor() is leaking GDI Objects. Here is how I fixed the problem:

    [DllImport(“gdi32.dll”)]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool DeleteObject(IntPtr hObject);

    private static Cursor InternalCreateCursor(System.Drawing.Bitmap bmp)
    {
    var iconInfo = new NativeMethods.IconInfo();
    Cursor retCursor = null;

    IntPtr hIcon = bmp.GetHicon();
    NativeMethods.GetIconInfo(hIcon, ref iconInfo);

    iconInfo.xHotspot = 0;
    iconInfo.yHotspot = 0;
    iconInfo.fIcon = false;

    SafeIconHandle cursorHandle = NativeMethods.CreateIconIndirect(ref iconInfo);
    retCursor = CursorInteropHelper.Create(cursorHandle);

    NativeMethods.DestroyIcon(hIcon);
    NativeMethods.DeleteObject(iconInfo.hbmColor);
    NativeMethods.DeleteObject(iconInfo.hbmMask);

    return retCursor;
    }

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