299971 - nsDragAndDrop.js doesn't allow dragging (drag and drop) within a tree widget

Status: RESOLVED WONTFIX

(Toolkit :: UI Widgets, defect)

Description

[Rory Parle]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-GB; rv:1.7.7) Gecko/20050414 Firefox/1.0.3
Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-GB; rv:1.7.7) Gecko/20050414 Firefox/1.0.3

nsDragAndDrop.js prevents drag and drop within any one element. The function
checkCanDrop() returns false if the source node is the same as the target node
(the one being dragged over). This works fine for dragging and dropping in
listboxes, for example, because the source node should be a listitem and the
target node will be a different listitem or the listbox itself.

We get problems for tree widgets because the entire tree is a single
treechildren element, so it's impossible to drag a node on the tree to a
different position using nsDragAndDrop.

The workaround is for the extension author to write the drag and drop javascript
code themself, but that pretty much defeats the purpose of nsDragAndDrop.js.
It's also worth noting that there is no easy way for an extension writer to
discover why their onDrop function isn't firing.

Reproducible: Always

Steps to Reproduce:

Comment 1

[Rory Parle]

The problem line is line 582 in /toolkit/content/nsDragAndDrop.js

Changing that from:
      this.mDragSession.canDrop = this.mDragSession.sourceNode != aEvent.target;

to:
      this.mDragSession.canDrop = this.mDragSession.sourceNode.tagName !=
"treechildren" && this.mDragSession.sourceNode != aEvent.target;

would be the simplest fix.

Comment 2

[Nickolay_Ponomarev]

*** Bug 101526 has been marked as a duplicate of this bug. ***

Comment 3

[Nickolay_Ponomarev]

I can make a patch for this, but I don't see the usefulness of using nsDragAndDrop with trees. Is there a way to get a row of a tree the drop happened on? If not, why is nsDragAndDrop useful here?

Comment 4

[Eric Jung [:ericjung]]

I'd like to be able to drag and drop items from one container (folder) in a tree into other containers in the same tree.

Can't one obtain the row on which the drop happened this way?

onDrop : function(evt, transferData, session) {
  var row = {}, col = {}, o = {};
  myTree.treeBoxObject.getCellAt(evt.clientX, evt.clientY, row, col, o);
}

Comment 5

[Nickolay_Ponomarev]

Attachment: patch

as suggested. Didn't test the XPFE part.

Comment 6

[[e-mail]]

Comment on attachment 211443 [details] [diff] [review]
patch

I don't think this is the right approach.

Comment 7

[[e-mail]]

Jan, would bug 120071 fix this, assuming you reply to my review question?

Comment 8

[Jan Varga [:janv]]

Yeah, I just replied in the bug.

Comment 9

[Neil Deakin]

The new drag and drop api added in bug 356295 makes nsDragAndDrop.js obsolete.