Drag-and-Drop Convenience API

The Common Desktop Environment provides a drag-and-drop convenience API to promote consistency and interoperability across the desktop, and to make it easier for developers to implement drag and drop.

The existing Motif API for drag and drop provides reasonable functionality to achieve a rendezvous between the source and destination applications in the transaction. It provides a framework for data transfer but leaves the actual data transfer details up to the application. For true consistency and interoperability between applications across the desktop, all applications must use the same data transfer protocols. The Common Desktop Environment drag-and-drop convenience API provides common data transfer routines.

Simplify Use for Developers

The existing Motif API for drag and drop is very flexible and, therefore, is somewhat difficult for nonexpert developers to use. The Common Desktop Environment drag-and-drop convenience API provides some convenience functions, described in the following paragraphs, that result in an API that is simpler and easier to use by providing the following services:

• Manages configuration and appearance of drag icons. Graphics are provided for the default source, state, and operation icons that make up the drag icon in Motif. The compositing of these icons checks the type of data being dragged.

• Enables animation for a drop. You can define an animation procedure that is called when the drop has completed.

• Provides data transfer using standard X selection targets for text, file, and buffer transfers. This data transfer allows interoperability with other applications that use the standard targets directly.

• Provides dual registration. You can register a text widget as a drop zone for data other than text and preserve the ability to accept text drops.

Establish Policy

The drag-and-drop API establishes policy in three areas:

• Common targets. Where available, existing selection targets defined by the Inter-Client Communication Conventions Manual (ICCCM) are used.

• Data transfer protocols. The API hides some of the details of data transfer and presents the data to the application in the form of some simple data structures.

• Default drag icons. Default drag icons are provided for applications that can accept them.

Provide Common Functionality

The drag-and-drop API provides common functionality in these areas:

• Supports the transfer of data as text, file names, and buffers

• Supports, through the data transfer framework, the addition of new, built-in protocols

Leverage Existing Motif API

The API for drag and drop does not invent a new drag-and-drop subsystem; rather, it uses the existing Motif API. In addition, since common data transfer protocols were chosen, where available, applications can interoperate at the selection protocol level without requiring global use of the new API.

The transfer of text and files use existing protocols. Buffer transfer uses new protocols.