Drag and Drop in Rich TextBox

In version 5.2.0 onwards it is possible to drag and drop external content into the Rich TextBox, this could be useful for many scenarios including the example we have here where we drag and drop emoticons from a toobar into the Rich TextBox.

Rich TextBox Drag and Drop

In this example we have a Rich TextBox and three emoticons above contained in a StackPanel.

<UserControl x:Class="RTBDragAndDrop.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:liquidRichText="clr-namespace:Liquid;assembly=Liquid.RichText"
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.RowDefinitions>
            <RowDefinition Height="32" />
            <RowDefinition />
        </Grid.RowDefinitions>
        <StackPanel x:Name="images" Grid.Row="0" Margin="2" Orientation="Horizontal">
            <Image Source="images/happy.png" />
            <Image Source="images/unhappy.png" />
            <Image Source="images/wink.png" />
        </StackPanel>
        <liquidRichText:RichTextBox x:Name="myRichTextBox" Grid.Row="1" Margin="2" RichText="Here is an example of dragging and dropping and external image into the RichTextBox! Drag the emoticon onto the RichTextBox." />
        <Image x:Name="dragging" Grid.RowSpan="2" IsHitTestVisible="False" VerticalAlignment="Top" HorizontalAlignment="Left" Stretch="None" Visibility="Collapsed" />
    </Grid>
</UserControl>


The C# contains the event handlers that make the drag and drop functionality possible:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Media.Imaging;

using Liquid;

namespace RTBDragAndDrop
{
    public partial class Page : UserControl
    {
        private Image _dragging = null;

        public Page()
        {
            InitializeComponent();

            LayoutRoot.MouseMove += new MouseEventHandler(Image_MouseMove);
            myRichTextBox.ContentDropped += new RichTextBoxEventHandler(richTextBox_ContentDropped);

            foreach (Image i in images.Children)
            {
                i.Stretch = Stretch.None;
                i.MouseLeftButtonDown += new MouseButtonEventHandler(Image_MouseLeftButtonDown);
            }
        }

        private void Image_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            myRichTextBox.ExternalDragStart = true;
            _dragging = (Image)sender;
            dragging.Visibility = Visibility.Visible;
            dragging.Source = _dragging.Source;
            UpdateDragging(e.GetPosition(LayoutRoot));
        }

        private void richTextBox_ContentDropped(object sender, RichTextBoxEventArgs e)
        {
            if (_dragging != null)
            {
                e.Parameter = new Image() { Source = _dragging.Source };
                CancelDrag();
            }
        }

        private void Image_MouseMove(object sender, MouseEventArgs e)
        {
            if (_dragging != null)
            {
                UpdateDragging(e.GetPosition(LayoutRoot));
            }
        }

        private void UpdateDragging(Point p)
        {
            dragging.Margin = new Thickness(p.X, p.Y, 0, 0);
            dragging.Visibility = Visibility.Visible;
        }

        private void CancelDrag()
        {
            dragging.Visibility = Visibility.Collapsed;
            _dragging = null;
        }
    }
}


We look for the MouseLeftButtonDown event on each of the emoticons, when one is clicked we begin the drag and drop operation.  The important line here is myRichTextBox.ExternalDragStart = true, this tells the Rich TextBox to "look" for MouseMove events that may occur over the control area.

When the user releases the mouse button the Rich TextBox generates the ContentDropped event and we set the e.Parameter property with either a UIElement or some RichText that we want to be inserted.

 
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