isEnabled/allowDrop don't update when set by a computed expression

[rniemeyer]

isEnabled/allowDrop don't update when set by a computed expression

[rniemeyer]

Hello-
This is an unfortunate by product of the way that the binding is designed. It uses computed observables that target the specific options, so if the value has already been unwrapped (an expression in the binding string) before the computed is setup, then the computed will not gain a dependency on the observable, as it will only receive the already calculated value.

It is not an easy one to handle. The choices are to unwrap all of the options in the "update" function and try to make sense of which option was actually being triggered (gets kind of messy) or split out the options into separate bindings (sortableAllowDrop and sortableIsEnabled). This might be a decent option, although it would likely require quite a bit of extra code, just to support this scenario.

I will think about it. I understand that the behavior is not obvious or necessarily consistent with what people are used to with simpler bindings.

[mbest]

This is related to knockout/knockout#500, which hopefully we can fix in the next version of Knockout.

Edit: Okay, it's slightly related, but even if the issue was fixed, the sortable binding wouldn't be able to individually subscribe to updates to isEnabled and allowDrop. It looks like you can do something like this though: isEnabled: function() { return !readOnly() }, allowDrop: function() { return !readOnly() }, and that's something that could possibly be added automatically with a future version of Knockout.