Wednesday, July 1, 2009

DragDropManager for WPF TreeViews and ListViews

Update: Please note that the download for this project has been moved here.

My new drag-and-drop manager for WPF, which handles both TreeViews and ListViews, is ready for download. Here's a list of features it includes:
  • Supports drag-drop operations among any number of TreeViews and/or ListViews.
  • Shows drag adorner while dragging among different TreeViews/ListViews.
  • Explicitly supports two types of drop events: ProcessMove for moving an item, and ProcessLink for linking one (see demo).
  • User controls where, relative to the item under the drag cursor, the item will be dropped: above, below, or (for TreeViews) within.
  • Spiffy animations for grabs, drops, and cancelled operations.
  • Auto-expand item if hovering over it during drag operation.
  • Auto-scroll TreeView or ListView if near top or bottom edge.
  • Works on the standard TreeView and ListView controls. No third-party TreeView or ListView control is required.
  • Not dependent upon a particular presentation-model (aka ViewModel) implementation. The pattern isn't even necessary in order to use the DragDropManager.

Demonstration Application

The demo consists of a TreeView that holds categories, and a ListView populated with the selected category's items. These two controls together have a total of three types of drag-drop operations setup on them.
  1. Move a category within the TreeView
  2. Move an item within the ListView
  3. Link an item with another category
The demo is available for download here. The drag-and-drop setup code in the demo looks like this:

dragMgr.AddControl<Category>( categoriesTreeView );
dragMgr.AddControl<Item>( itemsListView );
dragMgr.AddHandler<Category>( categoriesTreeView, dragMgr_ProcessMove );
dragMgr.AddHandler<Item>( itemsListView, dragMgr_ProcessMove );
dragMgr.AddHandler<Item, Category>( categoriesTreeView, dragMgr_ProcessLink );
dragMgr.GetLinkEffect += dragMgr_GetLinkEffect;

The first two lines indicate which controls will have their dragging managed. The following three lines add the event handlers whose job is to actually move or link the domain-model objects. The last line adds the custom link animations you will see in the demo.

The body of your ProcessMove and ProcessLink event handlers will depend on how you've architected your presentation-model. The demo app doesn't even use one, so the event handlers simply look like this:

void dragMgr_ProcessMove( object sender, MoveArgs<Category> moveArgs )
 moveArgs.oldPosition.parent.SubCategories.Remove( moveArgs.itemToMove );
  moveArgs.newPosition.childIndex, moveArgs.itemToMove );

void dragMgr_ProcessMove( object sender, FlatMoveArgs<Item> moveArgs )
 var category = (Category)categoriesTreeView.SelectedItem;
 category.Items.RemoveAt( moveArgs.oldIndex );
 category.Items.Insert( moveArgs.newIndex, moveArgs.itemToMove );

void dragMgr_ProcessLink( object sender, LinkArgs<Item, Category> e )
 e.TargetLoc.Items.Add( e.ItemToLink );


Troy said...

When I downloaded the demo I was fairly impressed. My current project requires me to move XML objects around and create entirely new objects based off the old ones if the types don't match, (don't ask). I already had everything working in a treeview in WPF just no drag & drop support. The demo project is short and concise and laid out in a manner you won't even need to look at the documentation. After I purchased I was able to integrate it into my project within an hour, (a couple of tweaks to my datasets, and attaching the events). It fixes a huge gap in the WPF framework in my opinion.

HappyNomad said...

IMPROVEMENT: Today a user observed that, while dragging, "there is a fair amount of flicker when you cross item boundaries". This has been fixed.

Anonymous said...

What caused the flickering?