# IDropSource

The IDropSource interface is one of the interfaces you implement to provide drag-and-drop operations in your application. It contains methods used in any application used as a data source in a drag-and-drop operation. The data source application in a drag-and-drop operation is responsible for:

- Determining the data being dragged based on the user’s selection.

- Initiating the drag-and-drop operation based on the user’s mouse actions.

- Generating some of the visual feedback during the drag-and-drop operation, such as setting the cursor and highlighting the data selected for the drag-and-drop operation.

- Canceling or completing the drag-and-drop operation based on the user’s mouse actions.

- Performing any action on the original data caused by the drop operation, such as deleting the data on a drag move.

IDropSource contains the methods for generating visual feedback to the end user and for canceling or completing the drag-and-drop operation. You also need to call the DoDragDrop, RegisterDragDrop, and RevokeDragDrop functions in drag-and-drop operations.

##### When to Implement

Implement IDropSource if you are developing a container or server application that can act as a data source for a drag-and-drop operation. The IDropSource interface is only required during the drag-and-drop operation.

If you implement the IDropSource interface, you must also implement the IDataObject interface on the same object to represent the data being transferred.

You can use the same implementation of IDataObject for drag-and-drop data as for the data object offered to the clipboard. Once you have implemented clipboard operations in your application, you can add drag-and-drop operations with only a little extra work.

##### When to Use

You don’t usually call IDropSource methods directly. Instead, your data source calls the DoDragDrop function when it detects that the user has initiated a drag-and-drop operation. Then, DoDragDrop calls the IDropSource methods during the drag-and-drop operation.

For example, DoDragDrop calls IDropSource::GiveFeedback when you need to change the cursor shape or when you need to provide some other visual feedback. DoDragDrop calls IDropSource::QueryContinueDrag when there is a change in the mouse button state to determine if the drag-and-drop operation was canceled or completed.

Methods in Vtable Order

IUnknown Methods | Description
QueryInterface | Returns pointers to supported interfaces.
AddRef | Increments reference count.
Release | Decrements reference count.

IDropSource Methods | Description
QueryContinueDrag | Determines whether a drag-and-drop operation should continue.
GiveFeedback | Gives visual feedback to an end user during a drag-and-drop operation.

See Also

DoDragDrop, IDataObject, IDropTarget