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.

The IDropSource interface contains the methods for generating visual feedback to the end user and for canceling or completing the drag-and-drop operation. The DoDragDrop function, RegisterDragDrop function, and RevokeDragDrop function are also used in drag-and-drop operations.

When to Implement

Implement the IDropSource interface 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 to represent the data being transferred.

The IDataObject interface can be the same as 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

Your IDropSource methods are called by the DoDragDrop function. Your application calls the DoDragDrop function when it detects that the user has initiated a drag-and-drop operation. Then, DoDragDrop calls your 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 canceled or completed.

Methods in Vtable Order

IUnknown Methods
Returns pointers to supported interfaces.
Increments reference count.
Decrements reference count.

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

See Also

DoDragDrop, IDataObject, IDropTarget

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