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Marionette.CollectionView

The CollectionView will loop through all of the models in the specified collection, render each of them using a specified childView, then append the results of the child view's el to the collection view's el. By default the CollectionView will maintain a sorted collection's order in the DOM. This behavior can be disabled by specifying {sort: false} on initialize.

CollectionView 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

CollectionView's childView

Specify a childView in your collection view definition. This must be a Backbone view object definition, not an instance. It can be any Backbone.View or be derived from Marionette.ItemView.

var MyChildView = Backbone.Marionette.ItemView.extend({});

Backbone.Marionette.CollectionView.extend({
  childView: MyChildView
});

Child views must be defined before they are referenced by the childView attribute in a collection view definition. Use getChildView to lookup the definition as child views are instantiated.

Alternatively, you can specify a childView in the options for the constructor:

var MyCollectionView = Backbone.Marionette.CollectionView.extend({...});

new MyCollectionView({
  childView: MyChildView
});

If you do not specify a childView, an exception will be thrown stating that you must specify a childView.

CollectionView's getChildView

The value returned by this method is the ChildView class that will be instantiated when a Model needs to be initially rendered. This method also gives you the ability to customize per Model ChildViews.

var FooBar = Backbone.Model.extend({
  defaults: {
    isFoo: false
  }
});

var FooView = Backbone.Marionette.ItemView.extend({
  template: '#foo-template'
});
var BarView = Backbone.Marionette.ItemView.extend({
  template: '#bar-template'
});

var MyCollectionView = Backbone.Marionette.CollectionView.extend({
  getChildView: function(item) {
    // Choose which view class to render,
    // depending on the properties of the item model
    if  (item.get('isFoo')) {
      return FooView;
    }
    else {
      return BarView;
    }
  }
});

var collectionView = new MyCollectionView();
var foo = new FooBar({
  isFoo: true
});
var bar = new FooBar({
  isFoo: false
});

// Renders a FooView
collectionView.collection.add(foo);

// Renders a BarView
collectionView.collection.add(bar);

CollectionView's childViewOptions

There may be scenarios where you need to pass data from your parent collection view in to each of the childView instances. To do this, provide a childViewOptions definition on your collection view as an object literal. This will be passed to the constructor of your childView as part of the options.

var ChildView = Backbone.Marionette.ItemView.extend({
  initialize: function(options) {
    console.log(options.foo); // => "bar"
  }
});

var CollectionView = Backbone.Marionette.CollectionView.extend({
  childView: ChildView,

  childViewOptions: {
    foo: "bar"
  }
});

You can also specify the childViewOptions as a function, if you need to calculate the values to return at runtime. The model will be passed into the function should you need access to it when calculating childViewOptions. The function must return an object, and the attributes of the object will be copied to the childView instance's options.

var CollectionView = Backbone.Marionette.CollectionView.extend({
  childViewOptions: function(model, index) {
    // do some calculations based on the model
    return {
      foo: "bar",
      childIndex: index
    }
  }
});

CollectionView's childViewEventPrefix

You can customize the event prefix for events that are forwarded through the collection view. To do this, set the childViewEventPrefix on the collection view.

var CV = Marionette.CollectionView.extend({
  childViewEventPrefix: "some:prefix"
});

var c = new CV({
  collection: myCol
});

c.on("some:prefix:render", function(){
  // child view was rendered
});

c.render();

The childViewEventPrefix can be provided in the view definition or in the constructor function call, to get a view instance.

CollectionView's childEvents

You can specify a childEvents hash or method which allows you to capture all bubbling childEvents without having to manually set bindings. The keys of the hash can either be a function or a string that is the name of a method on the collection view.

// childEvents can be specified as a hash...
var MyCollectionView = Marionette.CollectionView.extend({

  // This callback will be called whenever a child is rendered or emits a `render` event
  childEvents: {
    render: function() {
      console.log("a childView has been rendered");
    }
  }
});

// ...or as a function that returns a hash.
var MyCollectionView = Marionette.CollectionView.extend({

  childEvents: function() {
    return {
      render: this.onChildRendered
    }
});

This also works for custom events that you might fire on your child views.

// The child view fires a custom event, `show:message`
var ChildView = new Marionette.ItemView.extend({
  events: {
    'click .button': 'showMessage'
  },

  showMessage: function () {
    console.log('The button was clicked.');

    this.trigger('show:message');
  }
});

// The parent uses childEvents to catch that custom event on the child view
var ParentView = new Marionette.CollectionView.extend({
  childView: ChildView,

  childEvents: {
    'show:message': function () {
      console.log('The show:message event bubbled up to the parent.');
    }
  }
});

CollectionView's buildChildView

When a custom view instance needs to be created for the childView that represents a child, override the buildChildView method. This method takes three parameters and returns a view instance to be used as the child view.

buildChildView: function(child, ChildViewClass, childViewOptions){
  // build the final list of options for the childView class
  var options = _.extend({model: child}, childViewOptions);
  // create the child view instance
  var view = new ChildViewClass(options);
  // return it
  return view;
},

CollectionView's addChild

The addChild method is responsible for rendering the childViews and adding them to the HTML for the collectionView instance. It is also responsible for triggering the events per ChildView. In most cases you should not override this method. However if you do want to short circut this method, it can be accomplished via the following.

Backbone.Marionette.CollectionView.extend({
  addChild: function(child, ChildView, index){
    if (child.shouldBeShown()) {
      Backbone.Marionette.CollectionView.prototype.addChild.apply(this, arguments);
    }
  }
});

CollectionView's emptyView

When a collection has no children, and you need to render a view other than the list of childViews, you can specify an emptyView attribute on your collection view.

var NoChildrenView = Backbone.Marionette.ItemView.extend({
  template: "#show-no-children-message-template"
});

Backbone.Marionette.CollectionView.extend({
  // ...

  emptyView: NoChildrenView
});

CollectionView's getEmptyView

If you need the emptyView's class chosen dynamically, specify getEmptyView:

Backbone.Marionette.CollectionView.extend({
  // ...

  getEmptyView: function() {
    // custom logic
    return NoChildrenView;
  }

This will render the emptyView and display the message that needs to be displayed when there are no children.

If you want to control when the empty view is rendered, you can override isEmpty:

Backbone.Marionette.CollectionView.extend({
  isEmpty: function(collection) {
    // some logic to calculate if the view should be rendered as empty
    return someBoolean;
  }
});

CollectionView's emptyViewOptions

Similar to childView and childViewOptions, there is an emptyViewOptions property that will be passed to the emptyView constructor. It can be provided as an object literal or as a function.

If emptyViewOptions aren't provided the CollectionView will default to passing the childViewOptions to the emptyView.

var EmptyView = Backbone.Marionette.ItemView({
  initialize: function(options){
    console.log(options.foo); // => "bar"
  }
});

var CollectionView = Backbone.Marionette.CollectionView({
  emptyView: EmptyView,

  emptyViewOptions: {
    foo: "bar"
  }
});

Callback Methods

There are several callback methods that can be provided on a CollectionView. If they are found, they will be called by the view's base methods. These callback methods are intended to be handled within the view definition directly.

onBeforeRender callback

A onBeforeRender callback will be called just prior to rendering the collection view.

Backbone.Marionette.CollectionView.extend({
  onBeforeRender: function(){
    // do stuff here
  }
});

onRender callback

After the view has been rendered, a onRender method will be called. 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.CollectionView.extend({
  onRender: function(){
    // do stuff here
  }
});

onBeforeDestroy callback

This method is called just before destroying the view.

Backbone.Marionette.CollectionView.extend({
  onBeforeDestroy: function(){
    // do stuff here
  }
});

onDestroy callback

This method is called just after destroying the view.

Backbone.Marionette.CollectionView.extend({
  onDestroy: function(){
    // do stuff here
  }
});

onBeforeAddChild callback

This callback function allows you to know when a child / child view instance is about to be added to the collection view. It provides access to the view instance for the child that was added.

Backbone.Marionette.CollectionView.extend({
  onBeforeAddChild: function(childView){
    // work with the childView instance, here
  }
});

onAddChild callback

This callback function allows you to know when a child / child view instance has been added to the collection view. It provides access to the view instance for the child that was added.

Backbone.Marionette.CollectionView.extend({
  onAddChild: function(childView){
    // work with the childView instance, here
  }
});

onBeforeRemoveChild callback

This callback function allows you to know when a childView instance is about to be removed from the collectionView. It provides access to the view instance for the child that was removed.

Backbone.Marionette.CollectionView.extend({
  onBeforeRemoveChild: function(childView){
    // work with the childView instance, here
  }
});

onRemoveChild callback

This callback function allows you to know when a child / childView instance has been deleted or removed from the collection.

Backbone.Marionette.CollectionView.extend({
  onRemoveChild: function(childView){
    // work with the childView instance, here
  }
});

CollectionView Events

There are several events that will be triggered during the life of a collection view. Each of these events is called with the Marionette.triggerMethod function, which calls a corresponding "on{EventName}" method on the view instance (see above).

"before:render" event

Triggers just prior to the view being rendered. Also triggered as "collection:before:render" / onCollectionBeforeRender.

var MyView = Backbone.Marionette.CollectionView.extend({...});

var myView = new MyView();

myView.on("before:render", function(){
  alert("the collection view is about to be rendered");
});

myView.render();

"render" event

A "render:collection" / onRenderCollection event will also be fired. This allows you to add more than one callback to execute after the view is rendered, and allows parent views and other parts of the application to know that the view was rendered.

var MyView = Backbone.Marionette.CollectionView.extend({...});

var myView = new MyView();

myView.on("render", function(){
  alert("the collection view was rendered!");
});

myView.on("collection:rendered", function(){
  alert("the collection view was rendered!");
});

myView.render();

"before:destroy" event

Triggered just before destroying the view. A "before:destroy:collection" / onBeforeDestroyCollection event will also be fired

var MyView = Backbone.Marionette.CollectionView.extend({...});

var myView = new MyView();

myView.on("before:destroy:collection", function(){
  alert("the collection view is about to be destroyed");
});

myView.destroy();

"destroy" / "destroy:collection" event

Triggered just after destroying the view, both with corresponding method calls.

var MyView = Backbone.Marionette.CollectionView.extend({...});

var myView = new MyView();

myView.on("destroy:collection", function(){
  alert("the collection view is now destroyed");
});

myView.destroy();

"before:add:child" / "add:child" event

The "before:add:child" event and corresponding onBeforeAddChild method are triggered just after creating a new childView instance for a child that was added to the collection, but before the view is rendered and added to the DOM.

The "add:child" event and corresponding onAddChild method are triggered after rendering the view and adding it to the view's DOM element.

var MyCV = Marionette.CollectionView.extend({
  // ...

  onBeforeAddChild: function(){
    // ...
  },

  onAddChild: function(){
    // ...
  }
});

var cv = new MyCV({...});

cv.on("before:add:child", function(viewInstance){
  // ...
});

cv.on("add:child", function(viewInstance){
  // ...
});

"before:remove:child"

This is triggered after the childView instance has been removed from the collection, but before it has been destroyed.

cv.on("before:remove:child", function(childView){
  // ...
});

"remove:child" event

Triggered after a childView instance has been destroyed and removed, when its child was deleted or removed from the collection.

cv.on("remove:child", function(viewInstance){
  // ...
});

"childview:*" event bubbling from child views

When a child view within a collection view triggers an event, that event will bubble up through the parent collection view with "childview:" prepended to the event name.

That is, if a child view triggers "do:something", the parent collection view will then trigger "childview:do:something".

// set up basic collection
var myModel = new MyModel();
var myCollection = new MyCollection();
myCollection.add(myModel);

// get the collection view in place
var colView = new CollectionView({
  collection: myCollection,
  childView: MyItemView
});
colView.render();

// bind to the collection view's events that were bubbled
// from the child view
colView.on("childview:do:something", function(childView, msg){
  alert("I said, '" + msg + "'");
});

// hack, to get the child view and trigger from it
var childView = colView.children[myModel.cid];
childView.trigger("do:something", "do something!");

The result of this will be an alert box that says "I said, 'do something!'".

Also note that you would not normally grab a reference to the child view the way this is showing. I'm merely using that hack as a way to demonstrate the event bubbling. Normally, you would have your child view listening to DOM events or model change events, and then triggering an event of its own based on that.

before:render:collection event

The before:render:collection event is triggered before the collectionView's children have been rendered and buffered. It differs from the collectionsView's before:render in that it is only emitted if the collection is not empty.

render:collection event

The render:collection event is triggered after a collectionView's children have been rendered and buffered. It differs from the collectionViews's render event in that it happens only if the collection is not not empty.

CollectionView render

The render method of the collection view is responsible for rendering the entire collection. It loops through each of the children in the collection and renders them individually as an childView.

var MyCollectionView = Backbone.Marionette.CollectionView.extend({...});

// all of the children views will now be rendered.
new MyCollectionView().render();

CollectionView: Automatic Rendering

The collection view binds to the "add", "remove" and "reset" events of the collection that is specified.

When the collection for the view is "reset", the view will call render on itself and re-render the entire collection.

When a model is added to the collection, the collection view will render that one model in to the collection of child views.

When a model is removed from a collection (or destroyed / deleted), the collection view will destroy and remove that model's child view.

CollectionView: Re-render Collection

If you need to re-render the entire collection, you can call the view.render method. This method takes care of destroying all of the child views that may have previously been opened.

CollectionView's attachHtml

By default the collection view will append the HTML of each ChildView into the element buffer, and then call jQuery's .append once at the end to move the HTML into the collection view's el.

You can override this by specifying an attachHtml method in your view definition. This method takes three parameters and has no return value.

Backbone.Marionette.CollectionView.extend({

    // The default implementation:
  attachHtml: function(collectionView, childView, index){
    if (collectionView.isBuffering) {
      // buffering happens on reset events and initial renders
      // in order to reduce the number of inserts into the
      // document, which are expensive.
      collectionView.elBuffer.appendChild(childView.el);
    }
    else {
      // If we've already rendered the main collection, just
      // append the new children directly into the element.
      collectionView.$el.append(childView.el);
    }
  },

  // Called after all children have been appended into the elBuffer
  attachBuffer: function(collectionView, buffer) {
    collectionView.$el.append(buffer);
  },

  // called on initialize and after attachBuffer is called
  initRenderBuffer: function() {
    this.elBuffer = document.createDocumentFragment();
  }

});

The first parameter is the instance of the collection view that will receive the HTML from the second parameter, the current child view instance.

The third parameter, index, is the index of the model that this childView instance represents, in the collection that the model came from. This is useful for sorting a collection and displaying the sorted list in the correct order on the screen.

Overrides of attachHtml that don't take into account the element buffer will work fine, but won't take advantage of the 60x performance increase the buffer provides.

CollectionView's resortView

By default the CollectionView will maintain the order of its collection in the DOM. However on occasions the view may need to re-render to make this possible, for example if you were to change the comparator on the collection. By default CollectionView will call render when this happens, but there are cases where this may not be suitable. For instance when sorting the children in a CompositeView, you want to only render the internal collection.

var cv = new Marionette.CollectionView({
  collection: someCollection,
  resortView: function() {
    // provide custom logic for rendering after sorting the collection
  }
});

CollectionView's children

The CollectionView uses Backbone.BabySitter to store and manage its child views. This allows you to easily access the views within the collection view, iterate them, find them by a given indexer such as the view's model or collection, and more.

var cv = new Marionette.CollectionView({
  collection: someCollection
});

cv.render();


// retrieve a view by model
var v = cv.children.findByModel(someModel);

// iterate over all of the views and process them
cv.children.each(function(view){

  // process the `view` here

});

For more information on the available features and functionality of the .children, see the Backbone.BabySitter documentation.

CollectionView destroy

CollectionView implements a destroy method, which is called by the region managers automatically. As part of the implementation, the following are performed:

By providing an onDestroy event in your view definition, you can run custom code for your view that is fired after your view has been destroyed and cleaned up. This lets you handle any additional clean up code without having to override the destroy method.

Backbone.Marionette.CollectionView.extend({
  onDestroy: function() {
    // custom cleanup or destroying code, here
  }
});
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