In a Marionette CollectionView, how can I pass the index of the model (in the collection) to the ItemView?

Question

I have a CollectionView

class MyCollectionView extends Backbone.Marionette.CollectionView
  itemView: MyItemView

  itemViewOptions: ->
    {
      indexInCollection: ?
    }

And I want MyItemView to know at which index in the collection its model is at.

I suppose, in the MyItemView, I can find it out via

@model.collection.indexOf(@model)

But is there a way to pass it in directly into MyItemView from my Marionette CollectionView, using some internal Marionette mechanism? Is this index exposed somewhere already?

Answer 1

the itemViewOptions, when set up as a function, receives an item or model parameter. Use this to find the index:

class MyCollectionView extends Backbone.Marionette.CollectionView
  itemView: MyItemView

  itemViewOptions: (model) ->
    {
      indexInCollection: this.collection.indexOf(model)
    }

Answer 2

Since Marionette 2.0.0 you can do it with a childViewOptions function:

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

As explained in the Marionette documentation for childViewOptions

Answer 3

Just adding to the previous answer, if you want to use one of the options in one of your view templates, you can simply do it like this:

class Run.Question extends Backbone.Marionette.ItemView
    template: "mock/run/question"
    initialize: ->
        @model = @model.set index: @options.index

class Run.Content extends Backbone.Marionette.CompositeView
    template: "mock/run/content"
    itemView: Run.Question
    itemViewContainer: "div.data-box"
    itemViewOptions: (model) ->
        {
            index: @collection.indexOf(model) + 1
        }

This way, you can get access to the "index" variable in your template.