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Silverlight: Drag And Drop ListBoxItem to Canvas (using Telerik Control)

Posted By:Kunal Chowdhury       Posted Date: March 05, 2010    Points: 25    Category: Silverlight    URL: http://www.dotnetspark.com  

While surfing thru different forum I noticed that, lots of people are actually facing issues while trying to implement the drag and drop feature. The main problem arises while trying to drag from a ListBox to a panel like canvas. In this post, I will go thru the steps to demonstrate such feature.
 

Introduction
While surfing thru different forum I noticed that, lots of people are actually facing issues while trying to implement the drag and drop feature. The main problem arises while trying to drag from a ListBox to a panel like canvas. In this post, I will go thru the steps to demonstrate such feature.

Prerequisite

Here I will use Telerik control to give out the demonstration. You can download the trial version of the dlls from Telerik Silverlight Control Page. I have implemented the demo using Silverlight 4 Beta 1. The same thing is also possible in earlier version of Silverlight. You can download Silverlight SDK from Silverlight Site. To develop apps in Silverlight 4 you must need Visual Studio 2010 Beta 2 which you can download from Microsoft site.


Code Walk through

So, lets go for implementing the same. Create a Silverlight project. Lets create a ListBox and a Canvas inside the LayoutRoot:

<Grid x:Name="LayoutRoot" Background="White">
<
Grid.ColumnDefinitions>
<
ColumnDefinition Width="150"/>
<
ColumnDefinition Width="*"/>
Grid.ColumnDefinitions>
<
ListBox x:Name="lstBox" Margin="10" Grid.Column="0"/>
<
Canvas x:Name="cnvDropBox" Background="Yellow" Margin="10" Grid.Column="1"/>
Grid>

Now in the code behind, we have to register the Drag and Drop events for the ListBox & Canvas. Use RadDragAndDropManager class to register the same. 
RadDragAndDropManager.AddDragInfoHandler(lstBox, OnDragInfo);
RadDragAndDropManager.AddDragQueryHandler(lstBox, OnDragQuery);
RadDragAndDropManager.AddDropInfoHandler(cnvDropBox, OnDropInfo);
RadDragAndDropManager.AddDropQueryHandler(cnvDropBox, OnDropQuery);

RadDragAndDropManager.SetAllowDrop(cnvDropBox, true);

The implementation of the events will be as below: 

private void OnDragQuery(object sender, DragDropQueryEventArgs e)
{
if (e.Options.Status == DragStatus.DragQuery)
{
var draggedListBoxItem = e.Options.Source as Image;
e.Options.DragCue = draggedListBoxItem.Source;
e.Options.Payload = draggedListBoxItem.Source;
}

e.QueryResult = true;
e.Handled = true;
}

private void OnDragInfo(object sender, DragDropEventArgs e)
{
if (e.Options.Status == DragStatus.DragComplete)
{
// comment this block if you are going to clone
lstBox.Items.Remove(e.Options.Source);
}
}

private void OnDropInfo(object sender, DragDropEventArgs e)
{
var droppablePanel = e.Options.Destination;

if (e.Options.Status == DragStatus.DropComplete && droppablePanel is Canvas)
{
FrameworkElement dragableControl = null;
Point desiredPosition = new Point();
Point currentDragPoint = e.Options.CurrentDragPoint;
Point canvasPosition = cnvDropBox.TransformToVisual(null).Transform(new Point());

if (e.Options.Source is Image)
{
// create the new instance & update the necessary properties
// this step is require if you are going to make a clone
Image tempDragableControl = e.Options.Source as Image;
dragableControl = new Image() { Source = tempDragableControl.Source };
cnvDropBox.Children.Add(dragableControl);
}

desiredPosition.X = currentDragPoint.X - canvasPosition.X;
desiredPosition.Y = currentDragPoint.Y - canvasPosition.Y;
dragableControl.SetValue(Canvas.LeftProperty, desiredPosition.X);
dragableControl.SetValue(Canvas.TopProperty, desiredPosition.Y);
}
}


private void OnDropQuery(object sender, DragDropQueryEventArgs e)
{
var droppablePanel = e.Options.Destination;

if (e.Options.Status == DragStatus.DropDestinationQuery && droppablePanel is Canvas)
{
e.QueryResult = true;
e.Handled = true;
}
}

As I am using Image inside the ListBoxItem, hence OnDragQuery I am setting the Source as an Image to the DragCue & PayLoad properties. OnDragInfo I am removing item from the ListBox. If you don't want to remove the dragged image from the ListBox then just remove that line. OnDropInfo I am just placing the Image to the appropriate position which we will get as CurrentDragPoint in the DragDropEventArgs


Conclusion

This is a sample demonstration. So, you can now explore it more to fulfil your requirement.


Download Sample Application:  Drag And Drop ListBoxItem to Canvas Demo



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