Registering Objects as Drop Zones

If your application defines data types, follow these steps to ensure that it provides all the drag and drop behavior that you intend:

1. In your application, decide if you need to define any data types.

2. For each data type you define, decide whether you want the associated object to be a drop zone.

3. For each object that you want to register as a drop zone, decide which operations--move, copy, or link--you want to define.

4. For the drop operations that are valid for each object, define the appropriate drop actions (set the MOVE_TO_ACTION, COPY_TO_ACTION, and LINK_TO_ACTION attributes).

If your application displays icons for data objects, you may choose to support those icons as drop zones. If so, you need to query the MOVE_TO_ACTION, COPY_TO_ACTION, or LINK_TO_ACTION attributes to determine the drop behavior for those data objects. Objects should support drop operations only if the corresponding attribute value is not NULL. If all three attributes have NULL values, the object should not be registered as a drop site. Whenever you set at least one of these attributes for an object with a defined data type, your application registers that object as a drop zone.

When a user drags an object to a drop zone, your application determines which gesture (that is, which drag operation) was used to make the drop. Based on the drag operation and the drop zone's data type, the application retrieves a drop attribute from the data-typing database. It then calls DtActionInvoke, using the following two rules to determine its parameters:

1. If the user drops objects A and B onto object C, call DtActionInvoke with C, A and B as args. The action is the value of either MOVE_TO_ACTION, COPY_TO_ACTION, LINK_TO_ACTION of C. If object C is an action, the args list does not include C. Also, the action is C.

The File Manager, along with its directory and folder objects, exemplifies how the desktop uses the move, copy, and link drop attributes. A user can drag and drop objects (files) to directory folders. File Manager defines MOVE_TO_ACTION, COPY_TO_ACTION, and LINK_TO_ACTION actions for folder objects. These actions perform the appropriate file system move, copy, and link system functions.

See /usr/dt/appconfig/types/C/dtfile.dt for an example of how to define the MOVE_TO_ACTION, COPY_TO_ACTION, and LINK_TO_ACTION attributes. See Chapter 5, Integrating with Drag and Drop for information about how to use drag and drop.