Embedders who want to have these hooks made available should implement nsIClipboardDragDropHooks and use the command manager to send the appropriate commands with these parameters/settings:

command:  cmd_clipboardDragDropHook

params        value type   possible values
"addhook"     isupports    nsIClipboardDragDropHooks as nsISupports
"removehook"  isupports    nsIClipboardDragDropHooks as nsISupports

Note:

• Overrides/hooks need to be added to each window (as appropriate). Adding them to the first window does not enable them for every window.
• If more than one implementation is set for a window, the hooks will be called in the order they are added.
• Adding the same hook to the same window will not add a second call. Each hook can only be called once per user action/api.
• Not all hooks are guaranteed to be called. If there are multiple hooks set for a window, any of them has an opportunity to cancel the action so no further processing will occur.
• If any errors occur (without setting the boolean result) the default action will occur.
• AllowDrop() will be called MANY times during drag so ensure that it is efficient.

Method overview

Methods

allowDrop()

Tells gecko whether a drop is allowed on this content area.

boolean allowDrop(
  in nsIDOMEvent event,
  in nsIDragSession session
);

Parameters

event

The DOM event (drag gesture).

session

The drag session from which client can get the flavors present or the actual data.

Return value

true indicates to the Operating System that if a drop does happen on this browser, it will be accepted. Otherwise, false to indicates to the Operating System that drop is not allowed. On win32, this will change the cursor to "reject".

allowStartDrag()

Prevents the drag from starting.

boolean allowStartDrag(
  in nsIDOMEvent event
);

Parameters

event

The DOM event (drag gesture).

Return value

true if the drag can proceed. Otherwise, false to show the drag is canceled (Does not go to Operating System).

onCopyOrDrag()

Alters the flavors or data presented to the OS. Used for drag and copy actions. Because this can be called many times, it is highly recommended that the implementation be very efficient so user feedback is not negatively impacted.

boolean onCopyOrDrag(
  in nsIDOMEvent aEvent,
  in nsITransferable trans
);

Parameters

aEvent

The DOM event (drag drop). null if triggered by copy.

trans

The transferable holding the list of flavors and the data for each flavor.

Return value

true to indicate that copy/drag can proceed. Otherwise, false to indicate that the copy/drag is canceled, does not go to Operating System.

onPasteOrDrop()

Provide an alternative action to the built-in behavior when something is dropped on the browser or in an editor.

boolean onPasteOrDrop(
  in nsIDOMEvent event,
  in nsITransferable trans
);

Parameters

event

The DOM event (drag drop); null if triggered by paste.

trans

The transferable holding the list of flavors and the data for each flavor.

Return value

true to indicate the action was handled, do not perform built-in behavior. Otherwise, false to indicate the action was not overridden, do built-in behavior.

See also

• nsIClipboard