A Layout is a specialized hybrid between an ItemView and a collection of Region objects, used for rendering an application layout with multiple sub-regions to be managed by specified region managers.

A layout manager can also be used as a composite-view to aggregate multiple views and sub-application areas of the screen where multiple region managers need to be attached to dynamically rendered HTML.

For a more in-depth discussion on Layouts, see the blog post Manage Layouts And Nested Views With Backbone.Marionette

Basic Usage

The Layout extends directly from ItemView and adds the ability to specify regions which become Region instances that are attached to the layout.

html <script id="layout-template" type="text/template">   <section>     <navigation id="menu">...</navigation>     <article id="content">...</article>   </section> </script>

```js AppLayout = Backbone.Marionette.Layout.extend({ template: “#layout-template”,

regions: { menu: “#menu”, content: “#content” } });

var layout = new AppLayout(); layout.render(); ```

Once you’ve rendered the layout, you now have direct access to all of the specified regions as region managers.

```js MenuView()); MainContentView()); ```

Region Availability

Any defined regions within a layout will be available to the layout or any calling code immediately after instantiating the layout. This allows a layout to be attached to an existing DOM element in an HTML page, without the need to call a render method or anything else, to create the regions.

However, a region will only be able to populate itself if the layout has access to the elements specified within the region definitions. That is, if your view has not yet rendered, your regions may not be able to find the element that you’ve specified for them to manage. In that scenario, using the region will result in no changes to the DOM.

Re-Rendering A Layout

A layout can be rendered as many times as needed, but renders after the first one behave differently than the initial render.

The first time a layout is rendered, nothing special happens. It just delegates to the ItemView prototype to do the render. After the first render has happened, though, the render function is modified to account for re-rendering with regions in the layout.

After the first render, all subsequent renders will force every region to close by calling the close method on them. This will force every view in the region, and sub-views if any, to be closed as well. Once the regions have been closed, the regions will be reset so that they are no longer referencing the element of the previous layout render.

Then after the Layout is finished re-rendering itself, showing a view in the layout’s regions will cause the regions to attach themselves to the new elements in the layout.

Avoid Re-Rendering The Entire Layout

There are times when re-rendering the entire layout is necessary. However, due to the behavior described above, this can cause a large amount of work to be needed in order to fully restore the layout and all of the views that the layout is displaying.

Therefore, it is suggested that you avoid re-rendering the entire layout unless absolutely necessary. Instead, if you are binding the layout’s template to a model and need to update portions of the layout, you should listen to the model’s “change” events and only update the neccesary DOM elements.

Nested Layouts And Views

Since the Layout extends directly from ItemView, it has all of the core functionality of an item view. This includes the methods necessary to be shown within an existing region manager.

```js MyApp = new Backbone.Marionette.Application(); MyApp.addRegions({ mainRegion: “#main” });

var layout = new AppLayout();; MenuView()); ```

You can nest layouts into region managers as deeply as you want. This provides for a well organized, nested view structure.

Closing A Layout

When you are finished with a layout, you can call the close method on it. This will ensure that all of the region managers within the layout are closed correctly, which in turn ensures all of the views shown within the regions are closed correctly.

If you are showing a layout within a parent region manager, replacing the layout with another view or another layout will close the current one, the same it will close a view.

All of this ensures that layouts and the views that they contain are cleaned up correctly.

Custom Region Type

If you have the need to replace the Region with a region class of your own implementation, you can specify an alternate class to use with the regionType propery of the Layout.

js MyLayout = Backbone.Marionette.Layout.extend({   regionType: SomeCustomRegion  });

You can also specify custom Region classes for each region:

```js AppLayout = Backbone.Marionette.Layout.extend({ template: “#layout-template”,

regionType: SomeDefaultCustomRegion,

regions: { menu: { selector: “#menu”, regionType: CustomRegionTypeReference }, content: { selector: “#content”, regionType: CustomRegionType2Reference } } }); ```

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