Sortable: Allow cancel method to be called in start event

[macku]

Cancelling sortable on start callback throws error:

"this.helper is null"

Function: _cacheHelperProportions

Example: ​http://jsfiddle.net/9Ke8q/1/

[rs]

The documentation states of the cancel method:

Useful in the stop and receive callback functions.

but it does not say that the method would not work in other event handlers, which is clearly the case. So at least the documentation should be updated…

But I, too, think this feature could be very useful: not allowing the drag in the first place. This could also be solved by allowing the cancel option to be a function, calculating the “draggability” of an object on demand.

[petersendidit]

#8432 is a duplicate of this ticket.

[petersendidit]

#7640 is a duplicate of this ticket.

[petersendidit]

Duplicate of #4904.

[tj.vantoll]

This is not a duplicate of #4904 because that has to do with items being dropped and this is asking that calling the cancel method within the start method to work. Here's a test case against master that shows this is an issue - ​http://jsfiddle.net/tj_vantoll/2ZSpu/.

This should be reconsidered for the rewrite.