Problem when getting observableArray through computed observable

[morticue]

I made a fiddle showing the problem. The sortable list doesn't get updated when selecting a different option in the select list, whereas the foreach list gets updated without a hitch.

http://jsfiddle.net/qvrwy/

[rniemeyer]

@jofri Thanks for reporting this one. I can see the issue and how to address it. Will put a fix in this weekend.

[rniemeyer]

@jofri - put in a fix for this issue. Let me know how it looks for you. Here is your fiddle with the latest code: http://jsfiddle.net/rniemeyer/qvrwy/1/.

[mbest]

Why not just do it this way (computed returns array instead of observable array)?

http://jsfiddle.net/mbest/qvrwy/2/

[rniemeyer]

@mbest that is a fine idea, but it doesn't work in his case. The sortable binding doesn't want the unwrapped observableArray, as it needs to write back to it. In your fiddle, if you sort your items on top, they will not be reflected on the bottom.

In a lot of the bindings that I have worked on, I have avoided the update function completely and used very specific computed observables in the init. However, there are cases where the subscription only happens in the parsing of the binding string that this will not account for.

For example, in some cases people might want to use a function (not a computed observable) to return a value, because they need to call the same logic several times and want to pass a different argument into each (put myFunction(someArg) in binding) rather than clutter up the view model by creating a bunch of similar computed observables. In this case, the dependency might only happen while parsing the binding string. Really I think that it is something that we should look into for KO core. It would be nice if the call to valueAccessor() would really capture all of the dependencies, even if we can't know sooner that the binding was invalid.

[mbest]

Ryan, thanks for the detailed explanation. Very helpful.

Really I think that it is something that we should look into for KO core. It would be nice if the call to valueAccessor() would really capture all of the dependencies

This is one of the main features that I included to support independent binding evaluation. So hopefully this will get in soon.

[morticue]

@rniemeyer Works like a charm, great work!

[rniemeyer]

@mbest didn't realize that your independent bindings work would do this properly already. It is an issue that I wrestle with frequently.

[mbest]

@rniemeyer It wasn't something that I had specifically targeted but was supported almost automatically for independent bindings. I added some minor changes now so that it's supported in the 'dependent' binding mode also.