Planet XAML ~ Florian Krüsch's Blog on XAML, .NET, WPF and Silverlight

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[WPF wpf]
More Visual Feedback for Drag'n'Drop
by Florian Krüsch, July 20, 2007
Jaime's always a good source for some real world stuff.
His series of blog posts on drag'n'drop is a must read:
Drag and drop with custom visuals across windows... yeah :) I found out you can also use a Popup control to do the trick, which is the WPF way of rendering visuals to independent HWNDs:

CursorBoundPopup.cs
public class CursorBoundPopup : Popup {    protected override void OnOpened(EventArgs e)    {       base.OnOpened(e);       CompositionTarget.Rendering += CT_Rendering;    }    protected override void OnClosed(EventArgs e)    {       CompositionTarget.Rendering -= CT_Rendering;       base.OnClosed(e);    }    private void CT_Rendering(object sender, EventArgs e)    {       Win32.POINT p;       if (!Win32.GetCursorPos(out p)) return;       HorizontalOffset = (Double)p.X;       VerticalOffset = (Double)p.Y;    } }
Nice thing is, you can now style the dragged visual declaratively and use databinding for the visual brush:

<dd:CursorBoundPopup xmlns:dd="clr-namespace:DragAndDropWithGhost"                x:Name="dragPopup"                IsOpen="False"                     AllowsTransparency="True"                     HorizontalAlignment="Left" VerticalAlignment="Top"                     Placement="Absolute"                     PopupAnimation="Fade"     >       <Rectangle Width="{Binding Width,ElementName=dragElement}"                  Height="{Binding Height,ElementName=dragElement}"       >         <Rectangle.Fill>           <VisualBrush Visual="{Binding ElementName=dragElement}"                   Opacity="0.5" />         </Rectangle.Fill>       </Rectangle>     </dd:CursorBoundPopup>
The start drag routine (a little oversimplified maybe) then looks like this:

StartDragWithPopup
private void StartDragWithPopup(MouseEventArgs e) {     // prepare D&D data     DataObject data = new DataObject(System.Windows.DataFormats.Text.ToString(), "abcd");     // prepare D&D     DragSource.GiveFeedback += DragSource_GiveFeedback;     dragPopup.IsOpen = true;     // do D&D     try     {    DragDropEffects de = DragDrop.DoDragDrop(this.DragSource, data, DragDropEffects.Move);     }     // I got COM interop exceptions from time to time... so     catch { }     // done with D&D                 DragSource.GiveFeedback -= DragSource_GiveFeedback;     dragPopup.IsOpen = false; }
cheers,
Florian
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[IronRuby iron_ruby, DLR dlr, WPF wpf]
Scott Hanselmann und IronRuby
by Florian Krüsch, July 24, 2007

Scott Hanselmann, Alpha-Geek und bekennender Ruby-Fan wechselt zu Microsoft.
Ich habe keine Ahnung, was hinter Wesabe steckt, aber dass ich mich jetzt noch ewas tiefer mit meiner neuen "Hobby-Sprache" Ruby beschäftigen kann, ohne meine kuschelige .NET/WPF/ASP.net Ecke zu verlassen, ist schon fein.
WPF ist zwar noch etwas mühsam, aber für die Zukunft lässt sich absehen, wie sich WPF Apps aus performace-kritischen Teilen in C# und rails-ähnlichen Ruby Teilen zusammenstöpseln lassen werden.
cheers,
Florian

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