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Select2 allowclear and knockout.js

I use select2 and knockoutJs with this simple binding:
ko.bindingHandlers.select2 = {
init: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
var options = ko.toJS(valueAccessor()) || {};
setTimeout(function () {
$(element).select2(options);
}, 0);
}
};
Markup:
<select class="select2" style="width:100%" data-bind="optionsCaption: '',options: $root.items,optionsText: 'description',optionsValue: 'id', value: $root.selectedItem,select2: { placeholder: 'Select an item...',allowClear: true }"></select>
it works! Now I enabled the allowClear option in Select2 to clear dropdown to a placeholder value like Select an item....
If I click the x icon dropdown properly sets the placeholder but knockout don't update observable binded value!
I think I've to change custombinding adding something like this:
setTimeout(function () {
$(element).select2(options).on("select2-removed", function (e) {
ko.bindingHandlers.value.update(element, function () { return ''; });
});
...
but it won't work!

There are couple of issues.
1) the update in bindinghandler is to update DOM based on value change, you should never define an update callback with the ability to mutate your model.
The right way is, when define a new bindinghandler, use init callback to hook up all change events with the model, the update callback is merely a DOM drawing routine.
If your init provided DOM drawing (such as provided by select2), you don't need to define an update callback.
Hence the line ko.bindingHandlers.value.update(element, function () { return ''; }); only redraw the DOM, it doesn't do what you want.
2) the select2 binding you created has some holes.
first, value binding doesn't know the existence of select2 binding, that's where you struggled.
second, your select2 binding has to wait for other binding (the options binding) to finish DOM creation, what's why you use setTimeout. But ko provided a way to define sequence of the bindings, just look the source code of ko value binding, it's defined as 'after': ['options', 'foreach']
third, your select2 doesn't respond to outside change. For instance, if you have another UI to update $root.selectedItem (a normal select list), the change raised by that UI would not sync back to your select2.
The solution
Define select2 binding based on existing value binding (just found out it's not needed), and hook up all change events.
we don't need "select2-removed" event, it's all about "change" event.
select2 provided all drawing, we don't need update callback.
use a flag shouldIgnore to break the loop between value subscriber and select2 change event handler.
http://jsfiddle.net/huocp/8N3zX/6/
http://jsfiddle.net/huocp/8N3zX/9/
ko.bindingHandlers.valueSelect2 = {
'after': ['options'],
'init': function(element, valueAccessor, allBindings) {
// kind of extend value binding
// ko.bindingHandlers.value.init(element, valueAccessor, allBindings);
var options = allBindings.get('select2Options') || {};
$(element).select2(options);
var value = valueAccessor();
// init val
$(element).val(ko.unwrap(value)).trigger("change");
var changeListener;
if (ko.isObservable(value)) {
var shouldIgnore = false;
changeListener = value.subscribe(function(newVal) {
if (! shouldIgnore) {
shouldIgnore = true;
// this is just select2 syntax
$(element).val(newVal).trigger("change");
shouldIgnore = false;
}
});
// this demo only works on single select.
$(element).on("change", function(e) {
if (! shouldIgnore) {
shouldIgnore = true;
if (e.val == '') {
// select2 use empty string for unselected value
// it could cause problem when you really want '' as a valid option
value(undefined);
} else {
value(e.val);
}
shouldIgnore = false;
}
});
}
ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
if (changeListener) changeListener.dispose();
$(element).select2("destory");
});
}
};

Incorrect binding handling with Durandal composing

Durandal binds view model to view before it has attached, and when you try to check element sizes using jquery it always returns 0. That's because jQuery can't get correct sizes of element which is invisible or is in invisible container.
My binding handler, which limits text with some number of lines and replaces remaining text with ellipsis, is not working when durandal is binding page, but works after second updates, when element is visible
ko.bindingHandlers.ellipsis = {
update: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
ko.bindingHandlers.text.update(element, valueAccessor);
var lines = allBindings.get('lines');
var $element = $(element);
var lineHeight = 1.3;
var heigth = lines * (+$element.css('font-size').substr(0, 2)) * lineHeight;
while ($element.outerHeight() > heigth) {
$element.text(replaceLast);
}
function replaceLast(index, text) {
return text.replace(/\W*\s(\S)*$/, '...');
}
}
};
I had this problem also when I used jQuery.customSelect through binding handler and when I used it through binding callback manually

Use a Delayed Binding Handler.
From the Durandal docs,
Sometimes your binding handler needs to work with an element only after it is attached to the DOM and when the entire composition of the view is complete. An example of this is any code that needs to measure the size of an HTML element. Durandal provides a way to register a knockout binding handler so that it does not execute until the composition is complete. To do this, use composition.addBindingHandler. One common use is in focusing elements. If you have an existing registered binding handler, you can change its execution time simply by doing this:
So your bidning handler would become the following:
composition.addBindingHandler('ellipsis', {
update: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
ko.bindingHandlers.text.update(element, valueAccessor);
var lines = allBindings.get('lines');
var $element = $(element);
var lineHeight = 1.3;
var heigth = lines * (+$element.css('font-size').substr(0, 2)) * lineHeight;
while ($element.outerHeight() > heigth) {
$element.text(replaceLast);
}
function replaceLast(index, text) {
return text.replace(/\W*\s(\S)*$/, '...');
}
}
});

Meteor JS: What is the best way to store states for a specific template instance?

I'm learning about Session and reactive data sources in Meteor JS. They work great for setting global UI states. However, I can't figure out how to scope them to a specific instance of a template.
Here's what I'm trying to do
I have multiple contenteditable elements on a page. Below each is an "Edit" button. When the user clicks on the Edit button, it should focus on the element and also show "Save" and "Cancel" buttons.
If the user clicks "Cancel", then any changes are eliminated, and the template instance should rerender with the original content.
Here's the code I have so far
// Helper
Template.form.helpers({
editState: function() {
return Session.get("editState");
}
});
// Rendered
Template.form.rendered = function(e){
var $this = $(this.firstNode);
var formField = this.find('.form-field');
if (Session.get("editState")) formField.focus();
};
// Event map
Template.form.events({
'click .edit-btn' : function (e, template) {
e.preventDefault();
Session.set("editState", "is-editing");
},
'click .cancel-btn' : function (e, template) {
e.preventDefault();
Session.set("editState", null);
},
});
// Template
<template name="form">
<div class="{{editState}}">
<p class="form-field" contenteditable>
{{descriptionText}}
</p>
</div>
Edit
Save
Cancel
</template>
// CSS
.edit-btn
.cancel-btn,
.save-btn {
display: inline-block;
}
.cancel-btn,
.save-btn {
display: none;
}
.is-editing .cancel-btn,
.is-editing .save-btn {
display: inline-block;
}
The problem
If I have more than one instance of the Form template, then .form-field gets focused for each one, instead of just the one being edited. How do I make so that only the one being edited gets focused?

You can render a template with data, which is basically just an object passed to it when inserted in to a page.
The data could simply be the key to use in the Session for editState.
eg, render the template with Template.form({editStateKey:'editState-topForm'})
you could make a handlebars helper eg,
Handlebars.registerHelper('formWithOptions',
function(editStateKey){
return Template.form({editStateKey:editStateKey})
});
then insert it in your template with
{{{formWithOptions 'editState-topForm'}}} (note the triple {, })
Next, change references from Session.x('editState') to Session.x(this.editStateKey)/ Session.x(this.data.editStateKey)
Template.form.helpers({
editState: function() {
return Session.get(this.editStateKey);
}
});
// Rendered
Template.form.rendered = function(e){
var $this = $(this.firstNode);
var formField = this.find('.form-field');
if (Session.get(this.data.editStateKey)) formField.focus();
};
// Event map
Template.form.events({
'click .edit-btn' : function (e, template) {
e.preventDefault();
Session.set(this.editStateKey, "is-editing");
},
'click .cancel-btn' : function (e, template) {
e.preventDefault();
Session.set(this.editStateKey, null);
},
});
Note: if you are using iron-router it has additional api's for passing data to templates.
Note2: In meteor 1.0 there is supposed to be better support for writing your own widgets. Which should allow better control over this sort of thing.

As a matter of policy I avoid Session in almost all cases. I feel their global scope leads to bad habits and lack of good discipline regarding separation-of-concerns as your application grows. Also because of their global scope, Session can lead to trouble when rendering multiple instances of a template. For those reasons I feel other approaches are more scalable.
Alternative approaches
1 addClass/removeClass
Instead of setting a state then reacting to it elsewhere, can you perform the needed action directly. Here classes display and hide blocks as needed:
'click .js-edit-action': function(event, t) {
var $this = $(event.currentTarget),
container = $this.parents('.phenom-comment');
// open and focus
container.addClass('editing');
container.find('textarea').focus();
},
'click .js-confirm-delete-action': function(event, t) {
CardComments.remove(this._id);
},
2 ReactiveVar scoped to template instance
if (Meteor.isClient) {
Template.hello.created = function () {
// counter starts at 0
this.counter = new ReactiveVar(0);
};
Template.hello.helpers({
counter: function () {
return Template.instance().counter.get();
}
});
Template.hello.events({
'click button': function (event, template) {
// increment the counter when button is clicked
template.counter.set(template.counter.get() + 1);
}
});
}
http://meteorcapture.com/a-look-at-local-template-state/
3 Iron-Router's state variables
Get
Router.route('/posts/:_id', {name: 'post'});
PostController = RouteController.extend({
action: function () {
// set the reactive state variable "postId" with a value
// of the id from our url
this.state.set('postId', this.params._id);
this.render();
}
});
Set
Template.Post.helpers({
postId: function () {
var controller = Iron.controller();
// reactively return the value of postId
return controller.state.get('postId');
}
});
https://github.com/iron-meteor/iron-router/blob/devel/Guide.md#setting-reactive-state-variables
4 Collection data
Another approach is to simply state by updating data in your collection. Sometimes this makes perfect sense.
5 update the data context
Session is often the worse choice in my opinion. Also I don't personally use #3 as I feel like being less tied to iron-router is better incase we ever want to switch to another router package such as "Flow".

How to create a custom binding for jquery ui dialog? [duplicate]

I am trying to create knockoutjs bindings for jquery ui dialogs, and cannot get the dialog to open. The dialog element is created correctly, but seems to have display: none that calling dialog('open') doesn't remove. Also, the call to dialog('isOpen') returns the dialog object rather than a boolean.
I am using the latest knockoutjs and jquery 1.4.4 with jquery ui 1.8.7. I've also tried it with jQuery 1.7.1 with the same results. Here's my HTML:
<h1 class="header" data-bind="text: label"></h1>
<div id="dialog" data-bind="dialog: {autoOpen: false, title: 'Dialog test'}">foo dialog</div>
<div>
<button id="openbutton" data-bind="dialogcmd: {id: 'dialog'}" >Open</button>
<button id="openbutton" data-bind="dialogcmd: {id: 'dialog', cmd: 'close'}" >Close</button>
</div>
and this is the javascript:
var jQueryWidget = function(element, valueAccessor, name, constructor) {
var options = ko.utils.unwrapObservable(valueAccessor());
var $element = $(element);
var $widget = $element.data(name) || constructor($element, options);
$element.data(name, $widget);
};
ko.bindingHandlers.dialog = {
init: function(element, valueAccessor, allBindingsAccessor, viewModel) {
jQueryWidget(element, valueAccessor, 'dialog', function($element, options) {
console.log("Creating dialog on " + $element);
return $element.dialog(options);
});
}
};
ko.bindingHandlers.dialogcmd = {
init: function(element, valueAccessor, allBindingsAccessor, viewModel) {
$(element).button().click(function() {
var options = ko.utils.unwrapObservable(valueAccessor());
var $dialog = $('#' + options.id).data('dialog');
var isOpen = $dialog.dialog('isOpen');
console.log("Before command dialog is open: " + isOpen);
$dialog.dialog(options.cmd || 'open');
return false;
});
}
};
var viewModel = {
label: ko.observable('dialog test')
};
ko.applyBindings(viewModel);
I have set up a JSFiddle that reproduces the problem.
I am wondering if this has something to do with knockoutjs and event handling. I tried returning true from the click handler, but that did not appear to affect anything.

It looks like writing to the widget to .data("dialog") and then trying to operate on it is causing an issue. Here is a sample where .data is not used and the open/close is called based on the element: http://jsfiddle.net/rniemeyer/durKS/
Alternatively, I like to work with the dialog in a slightly different way. I like to control whether the dialog is open or closed by using an observable. So, you would use a single binding on the dialog itself. The init would initialize the dialog, while the update would check an observable to see if it should call open or close. Now, the open/close buttons just need to toggle a boolean observable rather than worry about ids or locating the actual dialog.
ko.bindingHandlers.dialog = {
init: function(element, valueAccessor, allBindingsAccessor) {
var options = ko.utils.unwrapObservable(valueAccessor()) || {};
//do in a setTimeout, so the applyBindings doesn't bind twice from element being copied and moved to bottom
setTimeout(function() {
options.close = function() {
allBindingsAccessor().dialogVisible(false);
};
$(element).dialog(options);
}, 0);
//handle disposal (not strictly necessary in this scenario)
ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
$(element).dialog("destroy");
});
},
update: function(element, valueAccessor, allBindingsAccessor) {
var shouldBeOpen = ko.utils.unwrapObservable(allBindingsAccessor().dialogVisible),
$el = $(element),
dialog = $el.data("uiDialog") || $el.data("dialog");
//don't call open/close before initilization
if (dialog) {
$el.dialog(shouldBeOpen ? "open" : "close");
}
}
};
Used like:
<div id="dialog" data-bind="dialog: {autoOpen: false, title: 'Dialog test' }, dialogVisible: isOpen">foo dialog</div>
Here is a sample:
http://jsfiddle.net/rniemeyer/SnPdE/

I made a little change to RP Niemeyer's answer to allow the dialog's options to be observables
http://jsfiddle.net/YmQTW/1/
Get the observables values with ko.toJS to initialize the widget
setTimeout(function() {
options.close = function() {
allBindingsAccessor().dialogVisible(false);
};
$(element).dialog(ko.toJS(options));
}, 0);
and check for observables on update
//don't call dialog methods before initilization
if (dialog) {
$el.dialog(shouldBeOpen ? "open" : "close");
for (var key in options) {
if (ko.isObservable(options[key])) {
$el.dialog("option", key, options[key]());
}
}
}

Adding this here because this is what most people find when searching on issues with jQuery UI Dialog and Knockout JS.
Just another option to avoid the "double binding" issue explained in the above answer. For me, the setTimeout() was causing other bindings to fail that require the dialog to be initialized already. The simple solution that worked for me was making the following changes to the accepted answer:
Add class='dialog' to any elements using the custom dialog binding.
Call this after page load, but before calling ko.applyBindings():
$('.dialog').dialog({autoOpen: false});
Remove the setTimeout inside the init of the custom binding, and just call the code directly.
Step 2 makes sure that any jQuery UI Dialogs have been initialized prior to any KO bindings. This way jQuery UI has already moved the DOM elements, so that you don't have to worry about them moving in the middle of applyBindings. The init code still works as-is (other than removing setTimeout) because the dialog() function will just update an existing dialog if already initialized.
An example of why I needed this is due to a custom binding I use to update the title of the dialog:
ko.bindingHandlers.jqDialogTitle = {
update: function(element, valueAccessor) {
var value = ko.utils.unwrapObservable(valueAccessor());
$(element).dialog('option', 'title', value);
}
};
I use a separate binding for this instead of the update function for the main dialog binding, because I only want to update the title, not other properties such as height and width (don't want the dialog to resize just because I change the title). I suppose I could also use update and just remove height/width, but now I can do both/either and not worry about the setTimeout being completed or not.

This is a variation of the great RP Niemeyer binding handler, which is useful for a differente scenario.
To allow the edition of an entity, you can create a <div> with edition controls, and use a with binding, which depends on an observable made on purpose for the edition.
For example, to allow the edition of a person, you can create and observable like editedPerson, and create a div with edition controls, with a binding like this:
data-bind="with: editedPerson"
When you add a person to the observable lke so:
vm.editedPerson(personToEdit);
the binding makes the div visible. When you finish the edition, you can set the observable to null, like so
vm.editedPerson(null);
and the div will close.
My variation of RP Niemeyer's bindingHandler allows to automatically show this div inside a jQuery UI dialog. To use it you simply have to keep the original with binding, and specify the jQuery UI dialog options like so:
data-bind="with: editedPerson, withDialog: {/* jQuery UI dialog options*/}"
You can get the code of my binding handler, and see it in action here:
http://jsfiddle.net/jbustos/dBLeg/
You can modify this code easily to have different defaults for the dialog, and even to make these defaults configurable by enclosing the handler in a js module, and adding a public configuration function to modify it. (You can add this function to the binding handler, and it will keep working).
// Variation on Niemeyer's http://jsfiddle.net/rniemeyer/SnPdE/
/*
This binding works in a simple way:
1) bind an observable using "with" binding
2) set the dialog options for the ui dialog using "withDialog" binding (as you'd do with an standard jquery UI dialog) Note that you can specify a "close" function in the options of the dialog an it will be invoked when the dialog closes.
Once this is done:
- when the observable is set to null, the dialog closes
- when the observable is set to something not null, the dialog opens
- when the dialog is cancelled (closed with the upper right icon), the binded observable is closed
Please, note that you can define the defaults for your binder. I recommend setting here the modal state, and the autoOpen to false.
*/
ko.bindingHandlers.withDialog = {
init: function(element, valueAccessor, allBindingsAccessor) {
var defaults = {
modal: false,
autoOpen: false,
};
var options = ko.utils.unwrapObservable(valueAccessor());
//do in a setTimeout, so the applyBindings doesn't bind twice from element being copied and moved to bottom
$.extend(defaults, options)
setTimeout(function() {
var oldClose = options.close;
defaults.close = function() {
if (options.close) options.close();
allBindingsAccessor().with(null);
};
$(element).dialog(defaults);
}, 0);
//handle disposal (not strictly necessary in this scenario)
ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
$(element).dialog("destroy");
});
},
update: function(element, valueAccessor, allBindingsAccessor) {
var shouldBeOpen = ko.utils.unwrapObservable(allBindingsAccessor().with),
$el = $(element),
dialog = $el.data("uiDialog") || $el.data("dialog");
//don't call open/close before initilization
if (dialog) {
$el.dialog(shouldBeOpen ? "open" : "close");
}
}
};
var person = function() {
this.name = ko.observable(),
this.age = ko.observable()
}
var viewModel = function() {
label= ko.observable('dialog test');
editedPerson= ko.observable(null);
clearPerson= function() {
editedPerson(null);
};
newPerson= function() {
editedPerson(new person());
};
savePerson= function() {
alert('Person saved!');
clearPerson();
};
return {
label: label,
editedPerson: editedPerson,
clearPerson: clearPerson,
newPerson: newPerson,
savePerson: savePerson,
};
}
var vm = viewModel();
ko.applyBindings(vm);
.header {
font-size: 16px;
font-family: sans-serif;
font-weight: bold;
margin-bottom: 20px;
}
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.11.4/jquery-ui.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/2.2.1/knockout-min.js"></script>
<link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.16/themes/base/jquery-ui.css" rel="stylesheet"/>
<h1 class="header" data-bind="text: label"></h1>
<div id="dialog" data-bind="with: editedPerson, withDialog: {autoOpen: false, title: 'Dialog test', close: function() { alert('closing');} }">
Person editor<br/>
Name:<br/><input type="text" data-bind="value: $data.name"/><br/>
Age:<br/><input type="text" data-bind="value: $data.age"/><br/>
<button data-bind="click: $parent.savePerson">Ok</button>
<button data-bind="click: $parent.clearPerson">Cancel</button>
</div>
<div>
<button data-bind="click: clearPerson">Clear person</button>
<button data-bind="click: newPerson">New person</button>
</div>
<hr/>
<div data-bind="text: ko.toJSON($root)"></div>

There's now this library that has all the JQueryUI bindings for KnockoutJS including, of course, the dialog widget.

Backbone.js : repopulate or recreate the view?

In my web application, I have a user list in a table on the left, and a user detail pane on the right. When the admin clicks a user in the table, its details should be displayed on the right.
I have a UserListView and UserRowView on the left, and a UserDetailView on the right. Things kind of work, but I have a weird behavior. If I click some users on the left, then click delete on one of them, I get successive javascript confirm boxes for all users that have been displayed.
It looks like event bindings of all previously displayed views have not been removed, which seems to be normal. I should not do a new UserDetailView every time on UserRowView? Should I maintain a view and change its reference model? Should I keep track of the current view and remove it before creating a new one? I'm kind of lost and any idea will be welcome. Thank you !
Here is the code of the left view (row display, click event, right view creation)
window.UserRowView = Backbone.View.extend({
tagName : "tr",
events : {
"click" : "click",
},
render : function() {
$(this.el).html(ich.bbViewUserTr(this.model.toJSON()));
return this;
},
click : function() {
var view = new UserDetailView({model:this.model})
view.render()
}
})
And the code for right view (delete button)
window.UserDetailView = Backbone.View.extend({
el : $("#bbBoxUserDetail"),
events : {
"click .delete" : "deleteUser"
},
initialize : function() {
this.model.bind('destroy', function(){this.el.hide()}, this);
},
render : function() {
this.el.html(ich.bbViewUserDetail(this.model.toJSON()));
this.el.show();
},
deleteUser : function() {
if (confirm("Really delete user " + this.model.get("login") + "?"))
this.model.destroy();
return false;
}
})

I always destroy and create views because as my single page app gets bigger and bigger, keeping unused live views in memory just so that I can re-use them would become difficult to maintain.
Here's a simplified version of a technique that I use to clean-up my Views to avoid memory leaks.
I first create a BaseView that all of my views inherit from. The basic idea is that my View will keep a reference to all of the events to which it's subscribed to, so that when it's time to dispose the View, all of those bindings will automatically be unbound. Here's an example implementation of my BaseView:
var BaseView = function (options) {
this.bindings = [];
Backbone.View.apply(this, [options]);
};
_.extend(BaseView.prototype, Backbone.View.prototype, {
bindTo: function (model, ev, callback) {
model.bind(ev, callback, this);
this.bindings.push({ model: model, ev: ev, callback: callback });
},
unbindFromAll: function () {
_.each(this.bindings, function (binding) {
binding.model.unbind(binding.ev, binding.callback);
});
this.bindings = [];
},
dispose: function () {
this.unbindFromAll(); // Will unbind all events this view has bound to
this.unbind(); // This will unbind all listeners to events from
// this view. This is probably not necessary
// because this view will be garbage collected.
this.remove(); // Uses the default Backbone.View.remove() method which
// removes this.el from the DOM and removes DOM events.
}
});
BaseView.extend = Backbone.View.extend;
Whenever a View needs to bind to an event on a model or collection, I would use the bindTo method. For example:
var SampleView = BaseView.extend({
initialize: function(){
this.bindTo(this.model, 'change', this.render);
this.bindTo(this.collection, 'reset', this.doSomething);
}
});
Whenever I remove a view, I just call the dispose method which will clean everything up automatically:
var sampleView = new SampleView({model: some_model, collection: some_collection});
sampleView.dispose();
I shared this technique with the folks who are writing the "Backbone.js on Rails" ebook and I believe this is the technique that they've adopted for the book.
Update: 2014-03-24
As of Backone 0.9.9, listenTo and stopListening were added to Events using the same bindTo and unbindFromAll techniques shown above. Also, View.remove calls stopListening automatically, so binding and unbinding is as easy as this now:
var SampleView = BaseView.extend({
initialize: function(){
this.listenTo(this.model, 'change', this.render);
}
});
var sampleView = new SampleView({model: some_model});
sampleView.remove();

I blogged about this recently, and showed several things that I do in my apps to handle these scenarios:
http://lostechies.com/derickbailey/2011/09/15/zombies-run-managing-page-transitions-in-backbone-apps/

This is a common condition. If you create a new view every time, all old views will still be bound to all of the events. One thing you can do is create a function on your view called detatch:
detatch: function() {
$(this.el).unbind();
this.model.unbind();
Then, before you create the new view, make sure to call detatch on the old view.
Of course, as you mentioned, you can always create one "detail" view and never change it. You can bind to the "change" event on the model (from the view) to re-render yourself. Add this to your initializer:
this.model.bind('change', this.render)
Doing that will cause the details pane to re-render EVERY time a change is made to the model. You can get finer granularity by watching for a single property: "change:propName".
Of course, doing this requires a common model that the item View has reference to as well as the higher level list view and the details view.
Hope this helps!

To fix events binding multiple times,
$("#my_app_container").unbind()
//Instantiate your views here
Using the above line before instantiating the new Views from route, solved the issue I had with zombie views.

I think most people start with Backbone will create the view as in your code:
var view = new UserDetailView({model:this.model});
This code creates zombie view, because we might constantly create new view without cleanup existing view. However it's not convenient to call view.dispose() for all Backbone Views in your app (especially if we create views in for loop)
I think the best timing to put cleanup code is before creating new view. My solution is to create a helper to do this cleanup:
window.VM = window.VM || {};
VM.views = VM.views || {};
VM.createView = function(name, callback) {
if (typeof VM.views[name] !== 'undefined') {
// Cleanup view
// Remove all of the view's delegated events
VM.views[name].undelegateEvents();
// Remove view from the DOM
VM.views[name].remove();
// Removes all callbacks on view
VM.views[name].off();
if (typeof VM.views[name].close === 'function') {
VM.views[name].close();
}
}
VM.views[name] = callback();
return VM.views[name];
}
VM.reuseView = function(name, callback) {
if (typeof VM.views[name] !== 'undefined') {
return VM.views[name];
}
VM.views[name] = callback();
return VM.views[name];
}
Using VM to create your view will help cleanup any existing view without having to call view.dispose(). You can do a small modification to your code from
var view = new UserDetailView({model:this.model});
to
var view = VM.createView("unique_view_name", function() {
return new UserDetailView({model:this.model});
});
So it is up to you if you want to reuse view instead of constantly creating it, as long as the view is clean, you don't need to worry. Just change createView to reuseView:
var view = VM.reuseView("unique_view_name", function() {
return new UserDetailView({model:this.model});
});
Detailed code and attribution is posted at https://github.com/thomasdao/Backbone-View-Manager

One alternative is to bind, as opposed to creating a series of new views and then unbinding those views. You'd accomplish this doing something like:
window.User = Backbone.Model.extend({
});
window.MyViewModel = Backbone.Model.extend({
});
window.myView = Backbone.View.extend({
initialize: function(){
this.model.on('change', this.alert, this);
},
alert: function(){
alert("changed");
}
});
You'd set the model of myView to myViewModel, which would be set to a User model. This way, if you set myViewModel to another user (i.e., changing its attributes) then it could trigger a render function in the view with the new attributes.
One problem is that this breaks the link to the original model. You could get around this by either using a collection object, or by setting the user model as an attribute of the viewmodel. Then, this would be accessible in the view as myview.model.get("model").

Use this method for clearing the child views and current views from memory.
//FIRST EXTEND THE BACKBONE VIEW....
//Extending the backbone view...
Backbone.View.prototype.destroy_view = function()
{
//for doing something before closing.....
if (this.beforeClose) {
this.beforeClose();
}
//For destroying the related child views...
if (this.destroyChild)
{
this.destroyChild();
}
this.undelegateEvents();
$(this.el).removeData().unbind();
//Remove view from DOM
this.remove();
Backbone.View.prototype.remove.call(this);
}
//Function for destroying the child views...
Backbone.View.prototype.destroyChild = function(){
console.info("Closing the child views...");
//Remember to push the child views of a parent view using this.childViews
if(this.childViews){
var len = this.childViews.length;
for(var i=0; i<len; i++){
this.childViews[i].destroy_view();
}
}//End of if statement
} //End of destroyChild function
//Now extending the Router ..
var Test_Routers = Backbone.Router.extend({
//Always call this function before calling a route call function...
closePreviousViews: function() {
console.log("Closing the pervious in memory views...");
if (this.currentView)
this.currentView.destroy_view();
},
routes:{
"test" : "testRoute"
},
testRoute: function(){
//Always call this method before calling the route..
this.closePreviousViews();
.....
}
//Now calling the views...
$(document).ready(function(e) {
var Router = new Test_Routers();
Backbone.history.start({root: "/"});
});
//Now showing how to push child views in parent views and setting of current views...
var Test_View = Backbone.View.extend({
initialize:function(){
//Now setting the current view..
Router.currentView = this;
//If your views contains child views then first initialize...
this.childViews = [];
//Now push any child views you create in this parent view.
//It will automatically get deleted
//this.childViews.push(childView);
}
});