Highlights of Architecture Components - app and web (from google shared sessions)
Looking at the convergence of the mobile web and app framework - the idea behind having a consistent framework irrespective of the channel is becoming fundamentally possible via the concept of establishing a consistent architectural pattern and optimising performance on the overall channel - whether an app or web.
Here are some highlights to give an insight on the Android app aspects.
1) Recycler Views and Activity/Fragment life cycles -
- Recycler Views served best via APIs.
Optimisation of Activity/Fragment - life cycles
Life Cycles form a core of the app.
- Solve the right problems - fundaments are core.
- Not throw the whole development out but try creating APIs which work well with other libraries or frameworks.
- Layers on top of existing mechanisms to guide how an app should be built.
- Focus on the scalability.
- Easier for everyone to write applications by removing boiler point code.
New Libraries - Architecture Components
- Lifecyles - included.
- Lifecycles - aware observables
- Lightweight ViewModel
- Object mapping library for db (for e.g sqlite)
Current Flow: Activity --> LocationListener --> onCreate --> initialise Context, onStart, onStop.
Changes to application might change --> onStart (for eg. user settings)
onStart --> checkUserStatus --> onStop (stop)
listenerStop --> onStop, onStart--> gets called after onStop which causes it to live forever and then drain resources.
Introducing --> LifeCycleOwner & LifeCycle Observer
Inside the activity --
New Flow: onCreate --> Initialise content, getLifeCycle --> location
Check current state with the lifeCycle - then attach the activity with the action using this listener state.
Use annotations -- for e.g. annotate a method using @OnLifeCycleEvent(ON_START).
So removed all excess code by introducing --> LifeCycle Aware Component.
Share resources across multiple LifeCycles --
LiveData<T> - observable data holder, LifeCycle aware -- which helps to manage subscriptions
- LocationListener extends LiveDatat --> LocationListener (Context) -- Active Observer (whose lifecycle is started)
- OnLocationChange(sending data back to the observer).
- No activities and fragments inside it
Using live data with query - while user rotates the phone (giving back new activity same view model)
webService.fetchUser triggered --> activity rotated --> again fetch called (problem)
Solution:
- put data inside the activities which extends viewModel
- inside getUser method --> first call get from web service else return the value
- inside activity --> get view model provider of this.
new activity started --> gets the view model --> when finished --> view model not needed.
Never reference views - RxJava.
Persistence
APIs on android --> Content providers, shared preferences, SQLite
Lot of program for getting data.
Use annotation based queries --> concept of DAO - data access object.
Interface FeedDao --> do load, inserts deleteAll, updateAll.
Supports Rx Java 2.
Compile time validation.
Intensive code migration
Google updates - Guide to App Architecture --> Develop --> Architecture Components - reference
guide.
UI controllers - activités & fragments
- observables
- keep UI up
- forwards user actions back to the view model
View model
- prepares data for the UI
- includes LiveData, Observables
- survides configuration changes
- gateway for UI controller
Repository
- saves as data store for all of applications
- provide simple data modifications
- co-ordinates fetching, syncing, persisting
Data Source
API data sources --
retrofit, cloud other OS.
User --> LiveData<User> --> UserRepository (What's the benefit -- testing?)
Put the code in the viewModel --> create the mock ViewModel to test the UI
Replace with mockRepository and it will work.
Can use a JUnit test.
Google Resources --> developer.android.com/arch
