Knockout options binding default value


With the move into MVC4 I have taken an interest in knockout. Microsoft seemed knockout options binding default value to include it with Knockout options binding default value so it was worth taking a look at. To my surprise it will undoubtedly save me some time and effort for complex ajax UIs. I have already hit a major stumbling block though with it. That is the fact that when you bind an object to a select knockout does not work as you would expect.

What you would expect is that no matter at what index the Font object was that it would select the proper item in the select menu when you loaded the page. This is not the case. Javascript does not consider two objects truly equal unless it is a reference to an exact object. Personally I think knockout. That is, it is able to knockout options binding default value objects as the values of a select, therefore it should have a mechanism to allow you to pre select one based on a pre determined key.

Faced with this problem, one of the easiest ways around is to change the way you bind to the select. Doing below you will properly pre select the value you want. However, the only issue here is that when you update the value in the select you essentially corrupt your data.

Obviously this solution is not ideal. In my search for a solution many people suggested holding the selected value in a separate observable. You pre populate that observable with a reference knockout options binding default value an object in the FontList array.

This would work for a lot of people, but not for me. When I fetch my data from the server it is already nicely formatted and held in a structured object. If I have to break that structure for every drop down then the usefulness of knockout starts to come into question. After toying with the idea of simply editing the knockout source code to make it work the way I expected I ended up finding out that making a custom binding handler would solve my issue.

Here it is below along with the usage. In my opinion this is not an idea solution because of all the data I had to pass back in the preSelect argument. In my particular situation because of the way my objects are structured I had to know all three parameters.

You situation may be different so adjust the code accordingly. I found that even though you set the selected index using knockout options binding default value method it does not update the referencing object, so the last line is there to do that. I also had to deal with this situation and I chose to comply with the way knockout meant it to be. In my viewmodel, once the initialization callbacks are completed, I run a sync method. This sync method goes over all the objects that need to get synced and syncs them to their appropriate arrays, similar to what you did with this binding.

I create a bindingHandler using init and update methods. On initI set the first value that come from observableand set change event to update knockout options binding default value observables associated to value and text. This handler will execute twice. At first time, select has no options bidden, so it will have no effect. But, at second time, with options bindden and created, every works fine.

I also ran into this issue previously, and created my own workaround. So, since we must use workarounds, I thought I would share mine. Notify me of follow-up comments by email. Notify me of new posts by email. I'm Ben Morris an asp. I run Ion Commerce for a living knockout options binding default value enjoy software development. February 7, at 4: March 28, at April 14, at 2: About Me I'm Ben Morris an asp.