Let's assume an observableArray with some entries. I wan't to have a complex html element for each of them. I used components to reuse templates:
<!-- ko foreach: searchResults -->
<entry class="..." params="entry: $data"></entry>
<!-- /ko -->
Rendering these items works perfectly. The problem: There's a "x"-button in each of these items which should allow the user to delete the items. Is there a way to manipulate the array from withing the array? Like accessing the parent?
I could solve it with proper ko-scoping:
<entry class="..." params="entry: $data, removeItem: $parent.removeItem"></entry>
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 have prepared a small jsfiddle here: http://jsfiddle.net/zb8jwre6/
Basically, I have observable array of sliders, and each slider should have it's own observable array of segments, which contain some properties for CSS-binding in HTML.
My first problem is that I'am not sure which foreach bind should i use:
This one doesn't work for some reason:
<div data-bind "foreach: $root.sliders">
<p data-bind="text: day"></p>
</div>
This one works, but I am not sure in which cases should I use this one:
<!-- ko foreach: sliders-->
<p data-bind="text: day"></p>
<!-- /ko -->
My second problem is that I don't know how to apply wanted CSS stylings from segment observable array.
I have tried this:
<div class='slider-segment' data-bind= "style: {left: segment_left, width:
segment_width, backgroundColor: segment_color}"></div>
But this does not work. I think I need to make those properties also as observables, but I am not sure how to do this properly in ViewModel
I would like to know what foreach binding should I use. When can I use "comment" foreach bindng and when do I use normal one, and I would like to know how to rework my code, so I can bind CSS properties from segments observable array.
Thank you!
I've changed
self.segments = ko.observableArray([segments]);
with
self.segments = ko.observableArray(segments);
See:
http://jsfiddle.net/x4a8pkmu/
I would like to know what foreach binding should I use. When can I use
"comment" foreach bindng and when do I use normal one, and I would
like to know how to rework my code, so I can bind CSS properties from
segments observable array
The "comment" syntax is useful if you do not want a container element. For example:
<ul>
<!-- ko foreach: myList -->
<li data-bind="text: myProp"></li>
<!-- /ko -->
</ul>
produces the same effects as:
<ul data-bind="foreach: myList">
<li data-bind="text: myProp"></li>
</ul>
The point of making a variable an observable is if you are going to change these values based on user interaction/server response, and then updating the UI. If the values are never going to change then using an observable for the style properties isn't helpful.
There is a very small difference between the two foreach loops - 'Comment' foreach does not have a parent div tag around the repeating child tags, while the other one does. So the outputs would look like:
Comment foreach:
<p>MON</p>
<p>TUE</p>
<p>WED</p>
Div foreach:
<div>
<p>MON</p>
<p>TUE</p>
<p>WED</p>
</div>
The comment foreach is useful for cases like these:
<ul>
<li class="header">Header item</li>
<!-- ko foreach: myItems -->
<li>Item <span data-bind="text: $data"></span></li>
<!-- /ko -->
</ul>
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())
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 Knockout 2.x, one could write:
<div data-bind="template: { name: 'my-template', foreach: elements }">
<div class="placeholder"><- these are the array elements.</div>
</div>
This way, a placeholder element could be appended to the rendered elements.
But, as I see, Knockout 3.0 changed this behavior: "placeholder" markup is just wiped out of the container element.
Is this intentional? Any workarounds?
One solution that I can immediately think of is adding "afterRender" to the template definition, but this has (according to my experiments with KO 3.0) a weird glitch: it doesn't fire for empty "elements" array.
Thank you in advance for your answers.
In comparing similar usages of templates to that of using the foreach option, I could not get the placeholder markup to render except for the specific case identified. As such, I'd assume that might not have been an intended usage.
Since the foreach option to the template binding doesn't provide anything that can't be replicated, one option would be to move the elements into the data option of a regular template and then "manually" provide the foreach markup either within a "container" element or containerless.
Containerless option
<script type="text/html" id="containerless-regular-template">
<!-- ko foreach: $data -->
<div data-bind="text:$data"></div>
<!-- /ko -->
<div class="placeholder"><- these are the array elements.</div>
</script>
If you want to get a little more fancy due to more dynamic requirements for the "placeholder", you could nest another template call at the end of the foreach markup within a containerless if binding. The outermost container would be limited but the contents would be dynamic.
<script type="text/html" id="my-nested-template">
<!-- ko foreach: $data.foreach -->
<div data-bind="text:$data"></div>
<!-- /ko -->
<!-- ko if: $data.template -->
<div data-bind="template: { name: template.name, data: template.data }"></div>
<!--/ko -->
</script>
<div data-bind="template: { name: 'my-nested-template', data: {foreach: [], template: {name: 'another-template-name', data: {}}} }">
Fiddle