17.2.1 Dragging values from a choice

To implement dragging in list-panel or tree-view supply the :drag-callback initarg. When the user drags, drag-callback receives a list of indices of the choice items being dragged.

The drag-callback should return a property list whose keys are the data formats (such as :string or :image) to be dragged, along with the values associated with each format.

(defun tree-drag-callback (pane indices)

  (list :string 

        (string (elt (capi:collection-items pane)

                     (first indices)))))

(defun fruits (x) 

  (case x 

    (:fruits (list :apple :orange))

    (:apple (list :cox :bramley))

    (:orange (list :blood-orange :seville))

    (t nil)))

(capi:contain

 (make-instance 'capi:tree-view

                :title "Fruit tree"

                :roots '(:fruits)

                :children-function 'fruits

                :drag-callback 'tree-drag-callback))

17.2.2 Dragging within an output-pane

To implement dragging items around within a single output-pane, include suitable callbacks on these gestures in its input-model :

In this case it is not necessary to call drag-pane-object and you can implement dropping in the same pane by a suitable callback for:

See this example:

17.2.3 Dragging values from an output-pane

To implement dragging from an output-pane include an appropriate callback on the (:button-1 :press) gesture in the pane's input-model . This callback should call drag-pane-object with arguments which provide the data formats and values associated with each format. You will also specify drop-callback in the destination pane(s), as described in Dropping.

See the example file in

17.2.4 Data formats

:string

Receives a string, potentially from another application. Is also understood by some other panes that expect text.

:image

Receives an image on Cocoa and GTK+. The value passed should be an image object. See Working with images for more information about images.When supplying an image for dragging (that is, including :image image in the plist argument of drag-pane-object or in the plist that is returned from the drop-callback ), the dragging mechanism frees the image (as by free-image) when it finishes with it (which will be at some indeterminate time later). If you need to pass an image which you want to use later, you should make a copy of it by make-sub-image.

When receiving an image (by calling drop-object-get-object with :image), the received image should also be freed when you finish with it. However, it will be freed automatically when the pane supplied to drop-object-get-object is destroyed, so you do not need to free it explicitly if freeing can wait (which is probably true in most cases).

See this example:

:filename-list

Receives a list of files. Is understood by other applications such as the Mac OS X Finder and Windows Explorer.

You can also use private formats, named by arbitrary keywords, which will work only in the same Lisp image.

17.2.5 Dragging a Cocoa title bar image

On Cocoa, if there is a drag image in an interface title bar, then dragging this image will by default return a list containing the interface pathname as :filename-list data. You could override this by providing a drag-callback for the interface.