Drag and Drop
The TreeView allows the user to reorder its nodes or transfer them to another TreeView instance through the drag-and-drop functionality.
Setup
To activate the drag-and-drop functionality, apply the kendoTreeViewDragAndDrop directive on a TreeView component.
The directive allows the nodes to be dragged and the TreeView will emit the following events:
nodeDragStart—Fires when the dragging begins. If prevented, the node won't be dragged.nodeDrag—Fires during dragging.nodeDrop—Fires when a node is dropped on a valid target. If prevented or marked as invalid, the subsequentaddItemandremoveItemevents will not be fired.addItem—Fires on the targeted TreeView after the node is dropped.removeItem—Fires on the source TreeView after the node is dropped.nodeDragEnd—Fires when the dragging ends.
In the following example the event arguments are logged to the console as they occur.
Built-in Editing Directive
The kendoTreeViewDragAndDrop directive allows items to be dragged and triggers the corresponding events. It doesn't, however, make any changes to the nodes order out-of-the-box, as the TreeView does not manage its own data.
Persisting and displaying the changes during dragging and dropping can be achieved either by manually handling the corresponding events and mutating the data, or by using the kendoTreeViewDragAndDropEditing directive. The latter uses an EditService which handles the addItem and removeItem events. You can supply your own EditService to the directive, or use it in combination with one of the two data binding directives.
Using with the Hierarchy Binding Directive
When the kendoTreeViewDragAndDropEditing directive is used in combination with the kendoTreeViewHierarchyBinding directive, the data binding directive sets the EditService of the editing directive. The initially passed data gets updated on every drag-and-drop interaction with no further setup.
Using with the Flat Binding Directive
The kendoTreeViewDragAndDropEditing directive can also be used with the kendoTreeViewFlatDataBinding directive to get out-of-the-box data editing.
Remote Binding
To display the changes from the drag-and-drop interaction, a local data set with the fetched nodes has to be persisted and mutated.
Flat Homogeneous Data
The following example showcases a custom directive that handles the remote data binding and editing during dragging and dropping.
Hierarchical Heterogeneous Data
When using the dragging and dropping with heterogeneous data, some constraints need to be applied on which the drag and drop operations are allowed.
The following example demonstrates remote binding to heterogeneous data, where items are allowed to be moved only in the same hierarchical level. Categories can only be reordered, products can only be reordered or transferred to another category.
Multiple TreeViews
The drag-and-drop directive allows items to be transferred from one TreeView to another. To mark a TreeView instance as a valid drop target, list it under the dropZoneTreeViews property of the other TreeView.
Note that the nodeDrop and addItem events are triggered on the target TreeView, while the removeItem event on the source TreeView.
The following example also demonstrates the node copy functionality (allowCopy), and a custom emptyItemPlaceholder directive which adds an item placeholder to the TreeView once all its items are transferred away.
Auto-Scrolling
When the content of the TreeView overflows, the first scrollable container starting from the TreeView element and going upwards will be scrolled when the drag clue is moved close to the top or the bottom of the container.
To disable this functionality, set the autoScroll input property to false.
By default, the scrolling will be performed by 1 pixel at every 1 millisecond, when the dragged item reaches the top or the bottom of the scrollable container. To customize this behavior, bind the autoScroll option to a DragAndDropScrollSettings object with the preferred step and interval values.
Expanded, Selected, and Checked States
During dragging and dropping the indices of the reordered nodes are updated in accordance with their new position. Thus, it is not advisable to rely on indices when persisting the expanded, selected, or checked state.
The following example showcases how the state of each node is tracked by an object property value.
Templates
The drag clue and drop hint can easily be customized according the design needs.
- To customize the drag clue, use the
kendoTreeViewDragClueTemplate. - To customize the drop hint, use the
kendoTreeViewDropHintTemplate.
