RadGrid exposes flexible event-driven mechanism to drag and drop grid records to
reorder them within the same grid, move them to different grid instance or drop
them over other html element on the page. In order to enable drag and drop of grid
items, you need to set the two boolean grid properties to true, namely:
<ClientSettings AllowRowsDragDrop="true">
<Selecting AllowRowSelect="True" EnableDragToSelectRows="false" />
</ClientSettings>
This will make the grid data rows draggable and the end user will be able to relocate them if needed.
Additionally, you can use the GridDragDropColumn. When a GridDragDropColumn is defined in the Columns collection of a GridTableView,
grid items can be grabbed only by the drag handle rendered in this column:
<telerik:GridDragDropColumn HeaderStyle-Width="18px">
</telerik:GridDragDropColumn>
The event-driven model which allows you to process and complete the drag and drop
operation can be separated into two phases: client-side and server-side phase.
Client-side phase
There are three client grid events exposed to handle drag/drop action: OnRowDragStarted(cancelable), OnRowDropping (cancelable) and
OnRowDropped.
- The OnRowDragStarted event can be intercepted if you want to perform
some conditional check and determine whether to cancel the drag operation or not. The syntax of the event handler follows the general client-side event signature
of RadGrid for ASP.NET AJAX. The row which is about to be dragged can be accessed through the get_gridDataItem() property of the second argument
passed in the OnRowDragStarted handler.
- The OnRowDropping event should be attached to identify the target element on which the dragged grid record is dropped. If this element does not meet your criteria for
acceptable target, cancel the operation by setting args.set_cancel(true)
where args is the second argument passed to the OnRowDropping handler. Additionally,
to determine the destination element or set it explicitly use the get_destinationHtmlElement()
and set_destinationHtmlElement() properties that can be accessed through
the args argument in the handler. Again, the syntax of the event handler follows
the general client-side event signature of RadGrid for ASP.NET AJAX.
- The OnRowDropped event can be handled if you would like to execute some extra code logic prior to the server-side OnRowDrop event rising. This event
cannot be cancelled and have the same set of arguments as the OnRowDropping client event.
Server-side phase
On the server there is a single event (named OnRowDrop). Subscribing
to this event allows you to reorder the items in the source grid or remove them
and append these rows to a destination grid instance. The sequence of actions you
will have to undertake in order to change the source structure may vary because
this depends strictly on the underlying data source and its data model. The common
logic in all cases, however, is that you can use three arguments passed in the handler
to accomplish the task:
- e.HtmlElement - holds the html element (or grid item)
- e.DestDataItem - the destination grid item object (either GridDataItem or GridNoRecordsItem)
- e.DraggedItems - a collection of GridDataItems which holds the rows that are taking part in the current drop operation
- e.DestinationGrid - a reference to the grid instance to which the row has been dragged to
- e.DestinationTableView - a reference to the table to which the row has been draggged to, points to the MasterTableView or detail table in hierarchical
grid
Combining the client and server part completes the circle and separates logically
each part of the drag and drop process until it is finalized. For richer end user
experience you can ajaxify the grid via RadAjaxManager and use RadAjaxLoadingPanel
indicators. Otherwise the drag and drop operation will be performed with plain postback.