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Marionette.ItemView

An ItemView is a view that represents a single item. That item may be a Backbone.Model or may be a Backbone.Collection. Whichever it is though, it will be treated as a single item.

ItemView extends directly from Marionette.View. Please see the Marionette.View documentation for more information on available features and functionality.

Additionally, interactions with Marionette.Region will provide features such as onShow callbacks, etc. Please see the Region documentation for more information.

Documentation Index

ItemView render

Unlike Backbone Views, all Marionette views come with a powerful render method. In fact, the primary differences between the views are the differences in their render methods. It goes without saying that it is unwise to override the render method of any Marionette view. Instead, you should use the onBeforeRender and onRender callbacks to layer in additional functionality to the rendering of your view.

The ItemView defers to the Marionette.Renderer object to do the actual rendering of the template.

The item view instance is passed as the third argument to the Renderer object's render method, which is useful in custom Renderer implementations.

You should provide a template attribute on the item view, which will be either a jQuery selector:

var MyView = Backbone.Marionette.ItemView.extend({
  template: "#some-template"
});

new MyView().render();

.. or a function taking a single argument: the object returned by ItemView.serializeData:

var my_template_html = '<div><%= args.name %></div>'
var MyView = Backbone.Marionette.ItemView.extend({
  template : function(serialized_model) {
    var name = serialized_model.name;
    return _.template(my_template_html)({
        name : name,
        some_custom_attribute : some_custom_key
    });
  }
});

new MyView().render();

Note that using a template function allows passing custom arguments into the .template function and allows for more control over how the .template function is called.

For more information on the _.template function see the Underscore docs.

Rendering A Collection In An ItemView

While the most common way to render a Backbone.Collection is to use a CollectionView or CompositeView, if you just need to render a simple list that does not need a lot of interaction, it does not always make sense to use these. A Backbone.Collection can be rendered with a simple ItemView, using the templates to iterate over an items array.

<script id="some-template" type="text/html">
  <ul>
    <% _.each(items, function(item){ %>
    <li> <%= item.someAttribute %> </li>
    <% }); %>
  </ul>
</script>

The important thing to note here, is the use of items as the variable to iterate in the _.each call. This will always be the name of the variable that contains your collection's items.

Then, from JavaScript, you can define and use an ItemView with this template, like this:

var MyItemsView = Marionette.ItemView.extend({
  template: "#some-template"
});

var view = new MyItemsView({
  collection: someCollection
});

// show the view via a region or calling the .render method directly

Rendering this view will convert the someCollection collection in to the items array for your template to use.

For more information on when you would want to do this, and what options you have for retrieving an individual item that was clicked or otherwise interacted with, see the blog post on Getting The Model For A Clicked Element.

Template-less ItemView

An ItemView can be attached to existing elements as well. The primary benefit of this is to attach behavior and events to static content that has been rendered by your server (typically for SEO purposes). To set up a template-less ItemView, your template attribute must be false.

<div id="my-element">
  <p>Hello World</p>
  <button class="my-button">Click Me</button>
</div>

var MyView = Marionette.ItemView.extend({
  el: '#my-element',

  template: false,

  ui: {
    paragraph: 'p',
    button: '.my-button'
  },

  events: {
    'click @ui.button': 'clickedButton'
  },

  clickedButton: function() {
    console.log('I clicked the button!');
  }
});

var view = new MyView();
view.render();

view.ui.paragraph.text();        // returns 'Hello World'
view.ui.button.trigger('click'); // logs 'I clicked the button!'

Another use case is when you want to attach a Marionette.ItemView to a SVG graphic or canvas element, to provide a uniform view layer interface to non-standard DOM nodes. By not having a template this allows you to also use a view on pre-rendered DOM nodes, such as complex graphic elements.

Events and Callback Methods

There are several events and callback methods that are called for an ItemView. These events and methods are triggered with the Marionette.triggerMethod function, which triggers the event and a corresponding "on{EventName}" method.

"before:render" / onBeforeRender event

Triggered before an ItemView is rendered.

Backbone.Marionette.ItemView.extend({
  onBeforeRender: function(){
    // set up final bits just before rendering the view's `el`
  }
});

"render" / onRender event

Triggered after the view has been rendered. You can implement this in your view to provide custom code for dealing with the view's el after it has been rendered.

Backbone.Marionette.ItemView.extend({
  onRender: function(){
    // manipulate the `el` here. it's already
    // been rendered, and is full of the view's
    // HTML, ready to go.
  }
});

"before:destroy" / onBeforeDestroy event

Triggered just prior to destroying the view, when the view's destroy() method has been called.

Backbone.Marionette.ItemView.extend({
  onBeforeDestroy: function(){
    // manipulate the `el` here. it's already
    // been rendered, and is full of the view's
    // HTML, ready to go.
  }
});

"destroy" / onDestroy event

Triggered just after the view has been destroyed.

Backbone.Marionette.ItemView.extend({
  onDestroy: function(){
    // custom destroying and cleanup goes here
  }
});

ItemView serializeData

Item views will serialize a model or collection, by default, by calling .toJSON on either the model or collection. If both a model and collection are attached to an item view, the model will be used as the data source. The results of the data serialization will be passed to the template that is rendered.

If the serialization is a model, the results are passed in directly:

var myModel = new MyModel({foo: "bar"});

new MyItemView({
  template: "#myItemTemplate",
  model: myModel
});

MyItemView.render();

<script id="myItemTemplate" type="template">
  Foo is: <%= foo %>
</script>

If the serialization is a collection, the results are passed in as an items array:

var myCollection = new MyCollection([{foo: "bar"}, {foo: "baz"}]);

new MyItemView({
  template: "#myCollectionTemplate",
  collection: myCollection
});

MyItemView.render();

<script id="myCollectionTemplate" type="template">
  <% _.each(items, function(item){ %>
    Foo is: <%= foo %>
  <% }); %>
</script>

If you need custom serialization for your data, you can provide a serializeData method on your view. It must return a valid JSON object, as if you had called .toJSON on a model or collection.

Backbone.Marionette.ItemView.extend({
  serializeData: function(){
    return {
      "some attribute": "some value"
    }
  }
});

Organizing UI Elements

As documented in Marionette.View, you can specify a ui hash in your view that maps UI elements by their jQuery selectors. This is especially useful if you access the same UI element more than once in your view's code. Instead of duplicating the selector, you can simply reference it by this.ui.elementName:

You can also use the ui hash values from within events and trigger keys using the "@ui.elementName": syntax

Backbone.Marionette.ItemView.extend({
  tagName: "tr",

  ui: {
    checkbox: "input[type=checkbox]"
  },

  onRender: function() {
    if (this.model.get('selected')) {
      this.ui.checkbox.addClass('checked');
    }
  }
});

modelEvents and collectionEvents

ItemViews can bind directly to model events and collection events in a declarative manner:

Marionette.ItemView.extend({
  modelEvents: {
    "change": "modelChanged"
  },

  collectionEvents: {
    "add": "modelAdded"
  }
});

For more information, see the Marionette.View documentation.

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