I need to get a value from the ViewModel using a value from an object located in a loop in the view/page.
<!-- ko foreach: ExtendedItems() -->
<tr>
<!-- ko foreach: PriceGroups() -->
<!-- ko if: DeductibleAmount() === $root.FindDeductibleValue($parent.Provider()) -->
<td> --Content-- </td>
<!-- /ko -->
<!-- /ko -->
</tr>
<!-- /ko -->
I have a function in the ViewModel that finds the correct value:
self.FindDeductibleValue = function (provider) {
return self.SelectedDeductibles.findObs('Provider', { Provider: provider }).Value();
}
This function works fine when I call it from the ViewModel, but I get "Cannot read property 'Value' of null at viewModel.self.FindDeductibleValue" when I try to use it in the view/page in the IF statement.
I've replaced $parent.Provider() with a number just to make sure that $parent.Provider() is not null, but it doesn't change the error I receive.
Is it not possible to use a function in an IF statement this way?
The issue here is "binding context". Couple things first though.
EDIT:
I just noticed that the method FindDeductibleValue() receives
something other than the currently iterated item, like knockout does
automatically. And the code within it seems a little strange. Can you
please post the full view models you're working with? I'm not
convinced there's enough context to answer the problem correctly here.
I would use the $parents array not $root in case the depth or pattern ever changes.
You don't need to invoke your observables in your bindings, knockout will do this for you. <!-- ko foreach: ExtendedItems --> instead of <!-- ko foreach: ExtendedItems() -->.
The main error you're encountering is a binding context issue, whereby when invoking the method from within the loop, you are essentially within a child context of the viewmodel. Unfortunately, JavaScript isn't able to tell you this. But it is telling you the problem. The child item doesn't have a Value property. In order to fix this you need to bind to the correct context I believe the code would be:
$parents[0].FindDeductibleValue.bind(null, $parent.Provider())
Related
I have a javascript object graph, an HTML form, and knockout bindings connecting the two. The form is complex, and sometimes the form needs to add some computed observables to some sub-object in our object graph, and I want to do that locally in the the HTML element that has the data-bind which relies on this, I don't want such knowledge somewhere in some global script.
<div class="widget" data-bind="foreach: subThing">
<script type="text/javascript">
$data._scratchpad = ko.computedObservable( ... );
</script>
...
<input data-bind="value: _scratchpad"/>
...
</div>
Now in the context of this script, the binding context is of course not yet set up, so the $data property is not yet available.
But is there some event that I might put on the element or something so I can catch when the bindings are first initialized so I can add the necessary things before the actual data-bind expressions want to refer to them?
I came up with a solution which is just a little ugly, but actually practically correct. Instead of this script element above, I just use a virtual element that contains nothing and whose only point is to get an if: condition evaluated, where then we put the statements into the body of a function that gets evaluated:
<div class="widget" data-bind="foreach: subThing">
<!-- ko if: (function() { if(!$data._scratchpad) {
$data._scratchpad = ko.computedObservable( ... );
}})() --> <!-- /ko -->
...
<input data-bind="value: _scratchpad"/>
...
</div>
The nice thing is that required no modification of the source code. And while it is just a little ugly with the boiler-plate code:
<!-- ko if: (function() { if(!...) {
...
}})() --> <!-- /ko -->
I could potentially use a custom binding's preprocessor to wrap this function around and say instead simply:
<!-- ko setup:
...
--> <!-- /ko -->
this is almost neat, but really not so much better that it's worth it.
It's kind-a handy that this virtual element definition is already in a comment, so there won't be any worries with the javascript code using special characters.
I'm trying to create a simple component in Knockout (3.3.0):
ko.components.register('test', {
viewModel: function() {
this.test = 'hello'
},
template:
`<span data-bind='if: 1, text: test'></span>`
});
ko.applyBindings();
See fiddle.
Now when I instantiate a <test></test> somewhere else, I get an error:
Multiple bindings (if and text) are trying to control descendant bindings of the same element. You cannot use these bindings together on the same element.
Is this really not possible? This would be like the most basic functionality to incorporate if you ask me. I know I could use <!-- ko text --> but what about setting other attributes like src and using if at the same time?
OK I found the (or at least, one possible) solution: Use <!-- ko if --><!-- /ko -->. This way, the template can be written like
<!-- ko if: 1-->
<span data-bind='text: test'></span>
<!-- /ko -->
I still don't think it's perfect, in Vue I would just do <span v-if='1'>{{text}}</span> bam done, but I guess not everything in this world can be as awesome as Vue...
I have an observableArray of posts. Each post should have its observableArray of comments, which i'm doing this way:
self.posts.subscribe(posts) {
ko.utils.arrayForEach(posts, function(post) {
post.comments = ko.observableArray()
})
}
So I have two foreachs:
<!-- ko foreach: posts -->
<div class="post">
...
<!-- ko forech: comments -->
<div class="comment">
<span class="delete_comment" data-bind="click: $root.deleteComment"></span>
</div>
<!-- /ko -->
<!-- /ko -->
In my viewmodel, the deleteComment function:
self.deleteComment = function(comment) {
//ajax..
// now i should remove this comment from the comments array
}
The problem here is that I just can't find a way to remove the comment from the comments array. I can't access the comments array from the viewmodel since it's dynamically created. I tried to bind the parent in the data-bind:
<span class="delete_comment" data-bind="click: $root.deleteComment.bind($parent)"></span>
But there's no difference, the first argument in deleteComment is still the comment object. How can I access the outer observableArray from inside deleteComment?
But there's no difference, the first argument in deleteComment is still the comment object.
Your bind changed what this is in the deleteComment function, not what the first argument is. If you don't need this for something else in deleteComment, you're good to go — use this.comments.
Or, of course, make the posts responsible for deleting their comments, rather than the root model.
In my app I have several screens that could appear due to a status, available, closed, ext. To make the different parts of the screens appear I was looking at using knockout if statements since the views and such all share the same values and such and it seems a waste to create that many files.
However in my research I could only find knockout if statement that looks like this
<!-- if: Availabilty() -->
<p>this appears</p>
<!-- /ko -->
And this will check if there are variables there and appear, but I can't seem to make it so it will check to see just what the variable that comes back is.
I have tried something like this
<!-- if: Availabilty === 'Available' -->
or
<!-- if: Availabilty() === 'Available' -->
Any help would be awesome!
You are missing the two letters ko: <!-- ko if: Availabilty() === 'Available' -->. Since I assume that Availabilty is an observable, the brackets are necessary to get its value.
lets say you have a simple Knockout loop
<!-- ko foreach: data -->
<div ... show something </div>
<!-- /ko -->
What is I would like to run some extra JavaScript code on each iteration of the loop (just want to put this code in the view and not the model). Not sure if using script tag is suitable, I don’t think that would work if the code was inside a knockout template as that would already be contained within a script tag.
There are a few other cases where I though been able to run normal JavaScript code inside knockout view would be useful. It is not something I would want to do often however it seems on the rare occasion it would be easier if I could just use regular JS rather than changing other things.
You shouldn't be doing that.
The reason is, you'd be mixing business logic and data, and that shouldn't happen.
You are able to execute a function during a foreach using the afterAdd handler
<!-- ko foreach: { data: data, afterAdd: myhandler } -->
<div ... show something </div>
<!-- /ko -->
Hope this helps.