358095 - use the copy cursor for copy drags in cocoa drag and drop

Status: RESOLVED FIXED

(Core :: Widget: Cocoa, defect)

Description

[Josh Aas]

We should use the copy cursor for copy drags in cocoa drag and drop. Right now everything is just a generic drag.

Comment 1

[Josh Aas]

Attachment: sort of fix v1.0

This should fix this in theory, but in practice gecko makes bad drag action choices so we end up using generic dragging all the time anyway.

For example - when you drag some text in the browser to a text box, you'd think gecko would consider it a copy but it actually considers it to be a move. That doesn't really make sense because you're not moving the text, you're copying it to the text field (obviously).

fwiw, this bug has existed in mozilla forever. We never used native drag cursors. Camino did in its own code, but it just always said the drag was a copy instead of trying to figure out what it actually was.

Comment 2

[Jesse Ruderman]

Does this patch fix bug 302403, bug 308389, and/or bug 410569?

Comment 5

[Markus Stange [:mstange]]

Neil, what's the right way to predict from cocoa code whether a drag will be a copy?

Comment 6

[Neil Deakin]

Since I'm not sure what event you're referring to, here is the way the effects are expected to work:

Before dragstart:
 effectAllowed is initialized to 'uninitialized'
 dropEffect is initialized to 'none'

After dragstart:
 effectAllowed, if set, is the effects that the source of the drag allows. If effectAllowed is 'uninitialized', this is equivalent to 'all'.
 dropEffect isn't currently used by drag service implementations, but could be used to specify the source's preferred effect. (I think this is the question that you are asking?)

After dragstart, one of the InvokeDragSession methods will be called. InvokeDragSessionWithImage and InvokeDragSessionWithSelection take a dataTransfer, although it may be null. The action supplied to these methods is equivalent to the effectAllowed, and is just a shorthand.

Before the drag and dragleave events:
 dragSession.dragAction isn't used, but the drag service should set the current desired state for older code
 effectAllowed is initialized from the value it had after the dragstart event
 dropEffect is set to whatever value it had last

After the drag and dragleave events:
 effectAllowed's value isn't used for anything
 dropEffect's value isn't used for anything
 dragSession.dragAction is unchanged

Before the dragenter and dragover events:
 dragSession.dragAction should be set by the drag service implementation to the desired drop effect, based on the keyboard state
 effectAllowed is initialized from the value it had after the dragstart event
 dropEffect is initialized from dragSession.dragAction, filtered based on effectAllowed

After the dragenter and dragover events:
 effectAllowed will specify the drop effects that the drop target allows
 dropEffect will specify the drop target's preferred drop effect
 dragSession.dragAction will be set to the dropEffect, filtered by the effectAllowed.

The drag service can use the effectAllowed and dragSession.dragAction to update the cursor, or can update it before the event based on the key state.

Before the drop and dragend events:
 effectAllowed is initialized from the value it had after the dragstart event
 dropEffect will specify the actual drop effect, set from the value it had after the last dragenter or dragover event
 dragSession.dragAction isn't used, but the drag service should set the actual drop effect for older code

Some bugs in the drag event handling code:

- when a drag from an another application occurs, the effectAllowed isn't initialized properly.
- nsContentAreaDragDrop::GetDragData could set the effectAllowed or dropEffect for the 'built-in' drags.

Comment 7

[Markus Stange [:mstange]]

I didn't really know how drag and drop works, so I wasn't sure myself what I was asking, but this summary is perfect and clears things up for me quite a bit. Thanks!

Comment 8

[Markus Stange [:mstange]]

Attachment: v2

Comment 9

[Markus Stange [:mstange]]

http://hg.mozilla.org/mozilla-central/rev/70994327b4f2