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Copying knockout object to another while updating the layout

When my user select one of the object in my observable array, I want to copy it to a "selectedObject". But when I do that, the layout binding on the "SelectedObject" are not updated.
So I've created an update method but I find it very difficult to maintain. is there a better way?
Here is my selected object ui:
<div class="row" data-bind="with: SelectedFlightObject">
<div>select object:</div>
<div data-bind="html: FlightNumber"></div>
</div>
Here is the js that I want to work but doesn't:
//this do not update the layout:
this.OnFlightClick = function (selectObject) {
this.SelectedFlightObject = selectObject;
}.bind(this);
Here is the js that update the ui but find it hard to maintain.
UpdateFlightObject: function (currentObj, newObj) {
currentObj.AirplaneType(newObj.AirplaneType());
currentObj.ArrivingDate(moment(newObj.ArrivingDate()));
currentObj.FlightNumber(newObj.FlightNumber());
currentObj.Duration(newObj.Duration());
currentObj.ArrivalCode(newObj.ArrivalCode());
currentObj.DeparturCode(newObj.DeparturCode());
},
this.OnFlightClick = function (selectObject) {
FlightFactory.UpdateFlightObject(this.SelectedFlightObject, selectObject);
}.bind(this);

Knockout requires you to use their observable wrappers. These wrappers are where the magic happens, once bound, they are what reports changes in values and receive user input back. Your code should look something like this.
Create:
this.SelectedFlightObject = ko.observable(someInitialValueOrNull);
Retrieve:
this.SelectedFlightObject();
Update:
this.SelectedFlightObject(someNewValueOrNull);

You should make your SelectedFlightObject observable so that when it changes your layout is updated.
this.OnFlightClick = function (selectObject) {
this.SelectedFlightObject(selectObject);
}.bind(this);
Your initial SelectedFlightObject would of course need to have some initial values for flight number, etc...
Remember that doing this does not create a new object

How to force knockoutjs to update UI (reevaluate bindings)

(I know there are other questions here asking the same thing; I've tried them and they don't apply here)
I have a collection being displayed by a Knockout JS foreach. For each item, the visible binding is set by call a method, based on something external to the item itself. When the externality changes, I need the UI to be redrawn.
A striped down version can be seen in this Fiddle: http://jsfiddle.net/JamesCurran/2us8m/2/
It starts with a list of four folder names, and displays the ones starting with 'S'.
<ul data-bind="foreach: folders">
<li data-bind="text: $data,
visible:$root.ShowFolder($data)"></li>
</ul>
<button data-bind="click:ToA">A Folders</button>
Clicking the button should display the ones starting with 'A' instead.
self.folders = ko.observableArray(['Active', 'Archive', 'Sent', 'Spam']);
self.letter = 'S';
// Behaviours
self.ShowFolder = function (folder)
{
return folder[0] === self.letter;
}
self.ToA = function ()
{
self.letter = 'A';
}
UPDATE:
After Loic showed me how easily this example could be fixed, I reviewed the differences between this example and my actual code. I'm using an empty object as a dictionary to toggle if an item is selected self.Selected()[item.Id] = !self.Selected()[item.Id];
The object being changed is already an observable. I assumed that Knockout didn't realize that the list is dependent on the external observable, but it does. What Knockout was missing was that the observable was in fact changing. So, the solution was simply:
self.Selected()[item.Id] = !self.Selected()[item.Id];
self.Selected.notifySubscribers();

Here's what I came up with:
What you have to understand is that Knockout is only "answering" to data changes in observables. If an observable changes, it will trigger every object that uses it. By making your self.letter an observable. You can simply change it's value and uses it somewhere like self.letter() and it will automagically redraw when needed.
http://jsfiddle.net/2us8m/3/
function WebmailViewModel() {
// Data
var self = this;
self.folders = ko.observableArray(['Active', 'Archive', 'Sent', 'Spam']);
self.letter = ko.observable('S');
// Behaviours
self.ShowFolder = function (folder)
{
return folder[0] === self.letter();
}
self.ToA = function ()
{
self.letter('A');
}
};
ko.applyBindings(new WebmailViewModel());
In case you have complex bindings, like storing an object inside an observable. If you want to modify that object you have multiple possible choices.
self.Selected()[item.Id] = !self.Selected()[item.Id];
You could change it to this by making everything "observables" but if my memory is right, it can become complicated.
self.Selected()[item.Id](!self.Selected()[item.Id]());
I remember I had one similar issue where I had dependency problem where I had to update a country, region, city. I ended up storing it as list inside an observable to prevent update on individual element change. I had something like this.
var path = PathToCity();
path[0] = 'all';
path[1] = 'all';
PathtoCity(path);
By doing this, the change would be atomic and there will be only one update. I haven't played a lot with knockout for a while. I'm not sure but I do believe that the last time I worked with knockout, it was able to "optimize" and prevent to redraw the whole thing. But be careful because if it is not able to guess that you didn't change many thing, it could redraw the whole observable tree (which could end up pretty bad in term of performance)
In your example, we could use the same behaviour with my modified example:
http://jsfiddle.net/2us8m/4/

knockout How to change the model binded to elements

I'm really just starting into knockout and so far it is pretty impressive. With that, there is also an issue I am running into.
I'm trying to take a list of binded objects and when on is clicked, I want it take that model and bind it to another view for further editing, no issues there. The problem I run into is that I get an error saying I cannot bind multiple times to the same element. I have read the ko.cleanNode([domElement]) can be used to circumvent it, but that is really meant to be used internally. I have done some searching and people mention you should use with but I don't think that applies to what I want to do.
Is there a way to apply the bindings but then just update the underlying model context?
Simplified jsfiddle example. My js code starts on like 119, above it the ko mapping plugin.

First, use the external resources to add external resources to your fiddle rather than pasting them into your fiddle.
Second, on your problem, the easiest way to do something like this is to have a SelectedItem property in your view model and bind the child view to it. Something like this:
var MyViewModel = function() {
var self = this;
self.MyItems = ko.observableArray();
self.SelectedItem = ko.observable();
}
var MyChildViewModel = function() {
var self = this;
self.SomeProperty = ko.observable();
}
Now populate MyItems with instances of MyChildViewModel and set SelectedItem to whichever item in MyItems you want to have as your child and bind the child view to SelectedItem:
<div id="theChildView" data-bind="with: SelectedItem">
<span data-bind="text: SomeProperty"></span>
</div>

how to render a collection using backbone?

I have this backbone that is working fine, i just want to render the collection is been fetched!
code:
var SearchView = Backbone.View.extend({
events: {
"keyup": "handleChange"
},
initialize: function(){
this.collection.bind("reset", this.updateView, this);
},
render: function(){
// this is where i need help
this.$el.next('#suggestions').append(// iterate over this.collection and apppend here) //
},
handleChange: function(){
var term = this.$el.val();
this.collection.search(term);
},
updateView: function() {
this.render();
}
});
I just want to iterate over this.collection and display the "text" attribute thats inside each collection and append it to the ('#suggestions') el. thanks

Focusing on your reset, render over collections issue, this is how I would do it. This way assumes that when you create your view, the $el is already present and you're passing it in through the View constructor so it's ready to go.
var SearchView = Backbone.View.extend({
template: _.template('<span><%= term %></span>');
initialize: function(){
this.collection.bind("reset", this.render, this);
},
render: function(){
this.addAllTerms();
return this;
},
addAllTerms: function() {
var self = this;
this.collection.each(function(model) {
self.addTerm(model);
});
},
addTerm: function(someModel) {
this.$el.next('#suggestions').append(this.template(someModel.toJSON()));
}
});
It's a bit different from your approach in a few ways. First, we utilize Underscore's template function. This could be anything from span to li to div whatever. We use the <%= %> to indicate that we're going to interpolate some value (which will come from our model.term attribute).
Instead of going to the handler then render, I just bind the collection to render.
The render() assumes we're always going to refresh the whole thing, build from scratch. addAllTerms() simply cycles through the collection. You can use forEach() or just each() which is the same thing except forEach() is 3 characters too long for my lazy bum. ;-)
Finally, the addTerm() function takes a model and uses it for the value that it will append to the #suggestions. Basically, we're saying "append the template with interpolated value". We defined the template function up above as this View object property to clearly separate the template from data. Although you could have skipped this part and just append('<span>' + someModel.get('term') + '</span>') or what not. The _.template() uses our template, and also takes any sort of object with the property that lines up with the one in our template. In this case, 'term'.
It's just a different way to do what you're doing. I think this code is a little more manageable. For example, maybe you want to add a new term without refreshing the whole collection. The addTerm() function can stand on its own.
EDIT:
Not that important but something I utilize with templates that I found useful and I didn't see it when I first started out. When you're passing the model.toJSON() into the template function, we're essentially passing all the model attributes in. So if the model is like this:
defaults: {
term: 'someTerm',
timestamp: '12345'
}
In our previous example, the attribute timestamp is also passed in. It isn't used, only <%= term %> is used. But we could easily interpolate it as well by adding it to the template. What I want to get at is that you don't have to limit yourself to data from one model. A complex template might have data from several models.
I don't know if it's the best way, but what I do is have something like this:
makeHash: function() {
var hash = {};
hash.term = this.model.get('term');
hash.category = anotherModel.get('category');
var date = new Date();
hash.dateAccessed = date.getTime();
return hash;
}
So you can easily build your own custom hash to throw into a template, aggregating all the data you want to interpolate into a single object to be passed into a template.
// Instead of .toJSON() we just pass in the `makeHash()` function that returns
// a customized data object
this.$el.next('#suggestions').append(this.template(this.makeHash()));
You can also easily pass in whole objects.
makeHash: function() {
var hash = {};
hash.term = this.model.get('term');
var animal = {
name: 'aardvark',
numLegs: 4
};
hash.animal = animal;
return hash;
}
And pass this into our template that looks like this:
template: _.template('<span><%= term %></span>
<span><%= animal.name %></span>
<span><%= animal.numLegs %></span>')
I'm not sure if this is the best way but it helped me understand exactly what data is going into my templates. Maybe obvious but it wasn't for me when I was starting out.

I found the solution to the problem, im gonna put it here for people that might want to know:
render: function(){
this.collection.forEach(function(item){
alert(item.get("text"));
});
}

KnockoutJS : How do I remove an item from a child array?

Issue:
I'm still learning knockoutJS, please guide me if my approach is wrong.
Here is my fiddle: http://jsfiddle.net/amitava82/wMH8J/25/
While onclick of edit, I receive the json model which is represented in the view and I want to remove certain items (child array) or actions (parent array) from the model (I removed add UI to add more Actions from the fiddle for simplicity) and then finally pass the model back to server.
Now, deleting from root level is easy. I'm stuck with deleting individual item which is ActionParamaters in ActionItems array.
Question:
How do I remove an item from a child array?

You can pass the clicked actionItem and the containing action array to deleteActionItem function as follows:
<!-- /ko -->
remove item
In your model you need to make every actionItem array observable using ko.mapping plugin (see edit function)
var viewModel = function() {
var self = this;
self.data = ko.observable();
self.edit = function() {
self.data ( ko.mapping.fromJS(editData) );
}
self.log = function() {
console.log(self.data())
}
self.deleteAction = function(data) {
//delete root node
self.data().remove(data)
}
self.deleteActionItem = function(data,actionItem) {
//delete items
data.ActionItems.remove(actionItem);
}
}
Then you will be able to remove the item from array in the deleteActionItem function and since the array is observable now, the result will reflect to binded dom element.

Sam, your fiddle data was too complicated. When asking questions, you will improve your chance of getting help if you distill your fiddle down to the relevant elements. I have cooked up a simple fiddle that illustrates nested arrays, and removal.
Here is the HTML, note that the remove function is inside the context of the array, so it calls a function on $parent instead of $root. This lets us target the context directly above, instead of the root.
<ul data-bind="foreach: editData">
<li>
<span data-bind="text: name"></span>
<button data-bind="click: $parent.removeParent">Remove Parent</button>
...
<!-- This line is on the child context -->
<button data-bind="click: $parent.removeChild">Remove Child</button>
</ul>​
Here is the parent model. Note the removal function here is for removing children. When the removeChild function is called, it is from the child context asking for $parent, which will call this remove.
var Parent = function(name, children) {
var self = this;
self.name = ko.observable(name);
self.children = ko.observableArray(children);
self.removeChild = function(child) {
self.children.remove(child);
};
};
Your fiddle also makes no use of models, which are an important aspect of MVVM development. You should consider going through the tutorials on the knockout site to get a better understanding of how to structure knockout applications. It will help you deal with problems like this much easier.