Page Dragging Overview

Page Dragging

Krypton provides its own drag and drop mechanism for moving KryptonPage instances between compatible controls. Note this is entirely separate from the standard drag and drop system that is exposed in Windows Forms using DoDragDrop and IDropTarget. Why provide a separate mechanism when windows already has a standard approach? Krypton provides more sophisticated visual feedback to the user that would be very difficult to achieve using the standard approach. It also allows us to provide something that is designed to be easy to use with Krypton controls.

Overview
You need three elements to perform page dragging. First you need a set of drop targets and for that we have the IDragTargetProvider. Any control that wants to act as a drop target needs to expose IDragTargetProvider so the drop targets for that control can be discovered. Second you need to allow drag operations to be initiated and for that we have the IDragPageNotify interface. Any control that wants to start a drag operation needs to take an instance of that IDragPageNotify interface and call its methods as required. Finally we need to an object that can orchestrate the operation. Krypton provides a class called DragManager that performs this orchestration for you.

IDragTargetProvider
Any control that needs to act as a drop target needs to expose this simple interface. The interface only has a single method called GenerateDragTargets that is called each time the set of drop targets is needed. Note that this means it is called each time a page drag operation is started so you could return a different set of targets for each drag operation. Passed into the method is a reference to the PageDragEndData instance which contains a list of all the pages being dragged. So you can examine the set of pages being dragged and decide which targets are relevant to those pages. Returned from the GenerateDragTargets call is a list of targets so you can provide none, one or many.

The Navigator implements this interface by returning just a single drop target. When the user drops on that target all the dragged pages are added to the end of the Navigator page list. Workspace also implements this interface but returns many different targets. The Workspace has many potential drop points such as the workspace edges or edges for each individual workspace cell and so the returned list of targets could be quite extensive. When the drop occurs the relevant target then performs the appropriate action.

For more detailed information see the Drag Enabling Controls section.

IDragPageNotify
Any control that needs to initiate dragging needs to do so my making calls into this interface. The interface exposes several methods such as PageDragStart, PageDragMove, PageDragEnd and PageDragQuit that are called by the source control as various actions occur. When the source control notices the left mouse button being pressed it would call PageDragStart. It would then call PageDragMove as the mouse is moved up until the release of the left button at which point PageDragEnd is called. If at any time the operation needs to be aborted then PageDragQuit is used.

Note that the control does not implement this interface but only makes calls into it. In order to do this the control needs to be provided with an instance of the IDragPageNotify interface. Both the Navigator and Workspace controls expose the DragPageNotify property for this very purpose. You can provide the same instance of the IDragPageNotify interface to more than one control as only one control at a time can be performing a drag operation.

For more detailed information see the Drag Enabling Controls section.

DragManager
Use the DragManager to orchestrate page dragging with the targets and provide visual feedback during the operation. Once you have created an instance of the class you can attach target providers by using the DragTargetProviders collection. For example you can add Navigator and Workspace instances that implement the IDragTargetProvider interface in the following way:-

      DragManager dm = new DragManager();  

      dm.DragTargetProviders.Add(kryptonNavigator1);  
      dm.DragTargetProviders.Add(kryptonWorkspace1);

The DragManager also implements the IDragPageNotify interface and so can be attached directly to the Navigator and Workspace controls like so:-

      kryptonNavigator1.DragPageNotify = dm;  
      kryptonWorkspace1.DragPageNotify = dm;  

For more detailed information see the DragManager section.