Technical Evaluation App

Rod Bailey Friday 01 Oct 2016

Summary

This is an Android application created as a technical exercise for Android Developers. It aims to illustrate an exemplary architecture (MVP) and the use of some core technologies and patterns that find common application in Android development. The requirements document is in a PDF file in the root directory of this project, and is called Android Developer - Step Code Review.pdf.

Screenshots

Note: These images only appear when the document is viewed on the Github web site.

Portrait Device Orientation

Landscape Device Orientation

Design Overview

Individual features of the application (e.g. "scenario1", "scenario2") are structured according to the MVP pattern. The overall app architecture is also inline with MVP but there is an additional "service" layer through which all remote data access occurs.

Other aspects of the design:

• I try and keep the views as simple and "dumb" (devoid of logic) as possible.
• As per usual MVP, each layer only communiccates with the layer above and below it. View never talks to Model directly, but only via the intermediary of the presenter. Model never talks to View directly, but only via the intermediary of the presenter.
• Runtime configuration properties are set in the file assets/config.properties
• Views and Presenters communicate via well defined interfaces e.g. IScenario1View, IScenario1Presenter.
• Presenters send messages to Models synchronously, via well defined interfaces.
• Models send messages to Presenters asynchrounsly using Events and an EventBus.

The Facade Pattern

The interface ITravelTimeService is a facade to backend service operations. There are two alternative implementations of it in FakeTravelTimeService and TravelTimeService. The former reads JSON data from the local file assets/sample.json, but the latter reads it over the internet. The config.properties file contains a property TravelTimeService.fake.use which specifies which implementation to actually use. The FakeTravelTimeService is useful for testing during development.

The Singleton Pattern

EventBusSingleton, AppDirectorSingleton, ConfigSingleton

The Observer Pattern

The publish / subscribe of events to the Otto event bus is an illustration of the Observer pattern.

The MVP Pattern

MVP is used at both the feature and architectural level. The View is either an Android Activity or an Android Fragment. For example MainActivity, Scenario1Fragment, Scenario2Fragment

#Orientation Changes

When the device orientation changes, the following occurs:

1. The MainActivity is destroyed and recreated by Android.
2. The fragments Sceario1Fragment and Scenario2Fragment are destroyed by Android
3. As part of their destruction, each fragment unregisters their associated presenters: IScenario1Presenter and IScenario2Presenter. See the onDestroy() methods of both.
4. The models behind each fragment are retained in the singleton AppDirectorSingleton. In this way, state has been preserved.
5. Android recreates Scenario1Fragment which, in its onViewCreated method creates a new Scenario1Presenter attached to the pre-existing Scenario1Model.
6. Android recreates Scenario2Fragment which, in its onViewCreated method creates a new Scenario2Presenter attached to the pre-existing Scenario2Model.
7. When each of the Presenters is recreated, they register themselves with the Otto Event Bus. Because they both @Subscribe to various property change events, the corresponding @Produce methods of the models are fired and there is a flood of events from Model to Presenter to bring the Presenter in line with the current state of the model.

I have not captured all of those attributes of the view's state that I might have e.g. the scroll position of scroll bars. Doing so would move the architecture closer to MVVP, but perhaps require a bidirectional binding library to achieve efficiently.

Android Versions

This app will work on Android versions from API level 16 onwards.

Libraries

The following third party libraries have been used:

• GSON for parsing of JSON
• ViewPagerIndicator for showing the circular page indicators
• Otto an event bus
• Volley for sending HTTP requests
• ButterKnife for injecting Views
• Android Support Library for backwards compatibility and the card widget
• Google Play Services for Google Maps
• Espresso for unit testing

Test Coverage

Current code coverage of the Espresso tests is 85%, as shown in the following report:

There are a few issues in the "Issue tracker" for this repository that should help get this up to 100%