Draggable: Allow setting containment during drag

[Mrten]

If you set a containment in the start event instead of in the default options, like this:

​https://jsfiddle.net/8wzdt8z5/8/

the intended containment between cell 2 and 4 only works the second time you drag cell 3.

If you add an (obvious internal) call to _setContainment it works the first time (see fiddle).

[Mrten]

An obvious fix for this is:

Index: draggable.js
===================================================================
--- draggable.js	(revision 29006)
+++ draggable.js	(working copy)
@@ -202,15 +202,15 @@
 		//Adjust the mouse offset relative to the helper if "cursorAt" is supplied
 		(o.cursorAt && this._adjustOffsetFromHelper(o.cursorAt));

-		//Set a containment if given in the options
-		this._setContainment();
-
 		//Trigger event + callbacks
 		if (this._trigger("start", event) === false) {
 			this._clear();
 			return false;
 		}

+		//Set a containment if given in the options
+		this._setContainment();
+
 		//Recache the helper size
 		this._cacheHelperProportions();

[Scott González]

It's not that this works the second time, it's that the call from the first time has been applied.

This option is not meant to be updated during a drag. I'm not sure if we want to add support for this either. We'll have to discuss this within the team.

In the meantime, you can accomplish this with a custom containment via the drag event. See ​https://jsfiddle.net/8wzdt8z5/9/

[Scott González]

We're tentatively accepting this feature for the rewrite. However, the proposed patch is too limited since it only supports one specific time that the option can be changed. A proper implementation would handle changes to containment at any point.