Implementing Drag Drop Operations for Browser Based WPF Applications (XBAP)

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Introduction

In the article, "Very simple WPF Drag and Drop Sample without Win32 Calls", I stated that because of not using Win32 calls, the resulting code should also work in the browser under partial trust. Well... I was wrong. It turned out that DragDrop.DoDragDrop(...) function would throw a SecurityException in an XBAP application under partial trust since DragDrop.DoDragDrop originates a so called OLE Drag'n Drop operation. For most applications, when we are dragging and dropping only WPF objects, no OLE transfer is necessary. So in this article, I give an example of simulating the Drag'n Drop functionality without DragDrop.DoDragDrop method that runs in a browser.

Using the Code

To use the code, simply unzip the file, start the project, compile and run the application.

There are two interesting things I had to figure out in order to make the application work in a browser: making sure that the picture of the cursor is visible and adopts a shape that we want. Both are implemented in ListView1_MouseMove callback for ListView1.MouseMove event.

To make the cursor visible, we simply do:

Mouse.SetCursor(Cursors.Hand);        

There is a problem that remains, however: I wanted the cursor to become a rectangle and there were no rectangle shapes among Cursors enumeration. And to top it all, you cannot use a bitmap image for a cursor in an XBAP partial trust application. To get around this problem, I made the cursor to be a semi-transparent rectangle visible only for the duration of the drag operation:

<Rectangle
    Name="CursorRectangle"
    Height="10" 
    Width="20" 
    Visibility="Hidden">
    <Rectangle.Fill>
        <SolidColorBrush Color="Blue" 
             Opacity="0.35"/>
    </Rectangle.Fill>
</Rectangle>

The following code ensures that the cursor rectangle does not move outside of the ListView control boundaries:

Point p = e.GetPosition(ListView1); // get the location of the mouse pointer

// get the boundaries of the ListView control (the cursor should not 
// be allowed to go beyond those boundaries
Rect bounds = VisualTreeHelper.GetDescendantBounds(ListView1); 

// set the vertical coordinate of the cursor to 
// coincide with the current mouse vertical coordinate
// as long as we are still within the boundaries of the 
// ListView control
if ( (bounds.Top < p.Y) && (bounds.Bottom > p.Y))
{
    Canvas.SetTop(CursorRectangle, p.Y);
}

// set the vertical coordinate of the cursor to 
// coincide with the current mouse horizontal coordinate
// as long as we are still within the boundaries of the 
// ListView control
if ((bounds.Left < p.X) && (bounds.Right > p.X))
{
    Canvas.SetLeft(CursorRectangle, p.X);
}

The rest of the code is very similar to that of "Very simple WPF Drag and Drop Sample without Win32 Calls" article.

History

• 16^th March, 2008: Initial post