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Published Jun 21, 2011 | Tommy Maintz | Tutorial | Easy

Last Updated Aug 10, 2011

This Tutorial is most relevant to Ext JS, 4.x.

The scalability, maintainability and flexibility of an application is mostly determined by the

quality of the application’s architecture. Unfortunately, it’s often treated as an afterthought.

Proofs of concept and prototypes turn into massive applications, and example code is

copied and pasted into the foundations of many applications. You may be tempted to do this

because of the quick progress that you see at the start of a project.

However, the time saved will be relatively low compared to the time spent on having to

maintain, scale and often refactor your application later in the project. One way to better

prepare for writing a solid architecture is to follow certain conventions and define application

views, models, stores and controllers before actually implementing them. In this article, we’ll

take a look at a popular application and discuss how we might architect the user interface to

create a solid foundation.

Code OrganizationCode Organization

Application architecture is as much

about providing structure and

consistency as it is about actual classes

and framework code. Building a good

architecture unlocks a number of

important benefits:

Every application works the same

way so you only have to learn it

once

It’s easy to share code between

apps because they all work the

same way

You can use Ext JS build tools to

create optimized versions of your

applications for production use

In Ext JS 4, we have defined

conventions that you should consider

following when building your

applications — most notably a unified

directory structure. This simple structure

places all classes into the app folder,

which in turn contains sub-folders to

7Like


namespace your models, views, controllers and stores.

While Ext JS 4 offers best practices on how to structure your application, there’s room to

modify our suggested conventions for naming your files and classes. For example, you might

decide that in your project you want to add a suffix to your controllers with “Controller,” e.g.

“Users” becomes “UsersController.” In this case, remember to always add a suffix to both the

controller file and class. The important thing is that you define these conventions before you

start writing your application and consistently follow them. Finally, while you can call your

classes whatever you want, we strongly suggest following our convention for the names and

structure of folders (controller, model, store, view). This will ensure that you get an optimized

build using our SDK Tools beta.

Striking a BalanceStriking a Balance

ViewsViews

Splitting up the application’s UI into views is a good place to start. Often, you are provided

with wireframes and UI mockups created by designers. Imagine we are asked to rebuild the

(very attractive) Pandora application using Ext JS, and are given the following mockup by our

UI Designer.

What we want to achieve is a balance between the views being too granular and too generic.

Let’s start by seeing what happens if we divide our UI into too many views.


Splitting up the UI into too many small views will make it difficult to manage, reference and

control the views in our controllers. Also, since every view will be in its own file, creating too

many views might make it hard to locate the view file where a piece of the UI or view logic is

defined.

On the other hand, we don’t want our views to be too generic because it will impact our

flexibility to change things.

In this scenario, each one of our views has been overly simplified. When several parts of a

view require custom view-logic, the view class will end up having too many responsibilities,

resulting in the view class becoming harder to maintain. In addition, when the designers

change their mind about the arrangement of the UI, we will end up having to refactor our view

definition and view logic; which can get tedious.

The right balance is achieved when we can easily rearrange the views on the page without


having to refactor them every time. For example, we want to make the Ad a separate view,

so we can easily move it around or even remove it later.

In this version, we’ve separated our UI by the roles of each view. Once you have a general

idea of the views that will make up your UI, you can still tweak the granularity when you’re

actually implementing them. Sometimes you may find that two views should really become

one, or a view is too generic and should be split into multiple views, but it helps to start out

with a good base. I think we’ve done that here.

ModelsModels

Now that we have the basic structure of our views in place, it’s time to look at the models. By

looking at the types of dynamic data in our UI, we can get an idea of the different models

needed for our application.

We’ve decided to use only two models — Song and Station. We could have defined two


more models called Artist and Album. However, just as with views, we don’t want to be too

granular when defining our models. In this case, we don’t have to separate artist and album

information because the app doesn’t allow the user to select a specific song by a given

artist. Instead, the data is organized by station, the song is the center point, and the artist and

album are properties of the song. That means we’re able to combine the song, artist and

album data into one model. This greatly simplifies the data side of our app. It also simplifies

the API that we have to implement on the server-side because we don’t have to load

individual artists or albums. To summarize, for this example, we’ll only have two models —

Song and Station.

StoresStores

Now that we’ve thought about the models our application will use, lets do the same for stores.

Figuring out the different stores you need is often relatively easy. A good strategy is to

determine all the data bound components on the page. In this case, we have a list with all of

the user’s favorite stations, a scroller with the recently played songs, and a search field that

will display search results. Each of these views will need to be bound to stores.

ControllersControllers

There are several ways you can distribute the application’s responsibilities across your

application’s controllers. Let’s start by thinking about the different controllers we need in this

example.


0 0 CommentsComments

Here we have two basic controllers — a SongController and a StationController. Ext JS 4

allows you to have one controller that can control several views at the same time. Our

StationController will handle the logic for both creating new stations as well as loading the

user’s favorite stations into the StationsList view. The SongController will take care of

managing the SongInfo view and RecentSong store as well as the user’s actions of liking,

disliking, pausing and skipping songs. Controllers can interact with each other by firing and

listening for application events. While we could have created additional Controllers, one for

managing playback and another for searching stations, I think we’ve found a good

separation of responsibilities.

Measure TwiceMeasure Twice, , Cut OnceCut Once

I hope that sharing our thoughts on the importance of planning your application architecture

prior to writing code was helpful. We find that talking through the details of the application

helps you to build a much more flexible and maintainable architecture.

Continue on to Architecting Your App in Ext JS 4, Part 2

Written by Tommy Maintz

Tommy Maintz is the original lead of Sencha Touch. With extensive knowledge of Object Oriented JavaScript

and mobile browser idiosyncracies, he pushes the boundaries of what is possible within mobile browsers.

Tommy brings a unique view point and an ambitious philosophy to creating engaging user interfaces. His

attention to detail drives his desire to make the perfect framework for developers to enjoy.

Follow Tommy on Twitter

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K Ramesh BabuK Ramesh Babu

What is the motivation behind the ‘stores’ concept? Should we call this

paradigm MVCS rather than MVC?

12 months ago

AliAli

Isn’t a store part of the model? At least, that’s how MVC sees it. Also don’t

understand the reason for a clientside “controller”. Should that contain all

11 months ago


Find Sencha developers at SenchaDevs © 2012 Sencha Inc. All rightsreserved.

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clientside handlers, and then redirect to the serverside MVC controller?

Would like to see this more detailed..

Ed SpencerEd Spencer Sencha EmployeeSencha Employee

Stores are really nothing more than a glorified array of Model *instances*.

They’re mostly used in our data-bound components like grids. We could

just use an array but the Store gives all kinds of benefits like sorting,

filtering and firing events whenever Model instances are added, removed or

updated, which makes acting on those changes much easier

11 months ago

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