Android state management Tutorial

Introduction
When creating android applications, that are not trivial, it is important to keep in mind that android activities, widgets, and services have somewhat autonomous lifecycles that are controlled by the operating system itself. This is profound impacts on how you have to think about applications, since they are no longer something unified, and instead are a lot of different parts that are being orchestrated somewhat randomly. For example, an application’s process can be terminated anytime, or its activities can be terminated, or its services can be restarted. If you do not plan for such diversity in lifecycle states when building each widget service or activity, you will have a really tough time syncing them all up in the final application.


What is the right way
It is best not to think of the application as one monolithic unified chunk of code. It is really difficult to think of the application in terms of the Linux process or its constituent activities, widgets and services. There are so many moving parts and pieces, it is easy to get disoriented in the mix of these things, especially when it comes to keeping track of lifecycle states. A simple example of this is the tendency of standard activities to restart when the screen orientation is changed. If you are not planning for this from the get go, here you have a very nasty surprise the first time the user changes the screen orientation. Especially if you are keeping state information in the scope of the activity object! This can be disabled in the android manifest, but it sets the stage for how you have to think differently about applications.

So what is the right way? It is best to keep state information persisted, along major checkpoints in the code. This means that you have to constantly save pertinent information to some service persistent store, whether to file or the database, it does not matter. As long as information is stored, you can have some hope of reconstituting the last known state of an activity, service, widget. So you have to make sure when these activities services or widgets are reconstituted that you check for any pre-existing stored state information. This will ensure that your applications can restart from failure (unintended or intended).

Service


In your service, make sure to keep track of all pertinent state information and save key information to persistent storage. This should be done when major state changes occur. Activities and widgets will also need to interact with your service. So it is really important to restore state on failure (and sense whether a start is clean or is a restart from failure). This will ensure that even if the service is restarted, any activities and widgets that rely on it will function moving forwards. For example, if your service was running a long-running task, before it got terminated, then on restart, it must ensure that that long-running task can be resumed, or restarted. Either ways any dependent widgets are activities would have to query the service to determine their initial state when they first bind to it. Alternatively, if you do not want to query the initial state, you can have the widgets and activities store their key pertinent state information to persistence as well.

Activity
When activity launches, and it depends on the service, it should start the service and bind to it. If the service was restarted unexpectedly and the activities not aware, it is best to have the activity query the service to figure out the initial state that should be set in the activity itself. Alternatively, the activity can store its own state information and restore it on startup. So if the activity kicks off some long-running process, it is best to store this state information to persistence. This way if the activity is restarted for whatever reason, it can pick up where it left off.

Summary
The key to all of this, is to make sure that key pertinent state information is persisted by an activity or service as it progresses through its lifecycle. You can implement complicated syncing between an activity and the service, to ensure that they are in the correct state at startup, but it might just be easier for each of the parties involved to store this information separately and restore it independently on startup or restart (and detect if start is clean or is a restart from failure). This way, you can create applications that are resilient to process terminations, service restarts, and even device restarts.

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10 Best Open Source Android Applications

I used to study code from famous open source projects to check out how others execute specific features as well as to learn from them. (I am a firm believer of the fact that you need to read good code to write good code)

Not Long Ago I have been following up a selection of good open source Android apps development and considered itemizing them here in order that it could be useful for many others.
Example Apps by Android Team.

Could there be a better way to start off without going through the code of the developers who developed the framework? These are 15 various android sample apps developed by the primary developers of the Android framework. These include a few games, photostream, time display, home display shortcuts etc.

url : http://code.google.com/p/apps-for-android/

Remote Droid

RemoteDroid is undoubtedly an android app which turns your phone into a wireless keyboard and mouse along with touchpad, using your own wireless network. You can learn lot of things like linking to a network, managing user finger motion etc from its source.

url: http://code.google.com/p/remotedroid/

TorProxy and Shadow

TorProxy is an implementation of Tor for Android mobiles. Along with Shadow, it enables you to surf internet site anonymously through your cell phone. You can study regarding tunnelling socket connections, managing cookies etc by reading it’s source code.

url: http://www.cl.cam.ac.uk/research/dtg/code/svn/android-tor/ and http://www.cl.cam.ac.uk/research/dtg/android/tor/

Android SMSPopup

It is an Android app that will intercepts incoming text messages and shows them in the pop-up window. Besides becoming a time saver, this app also shows us the best way to interface with the built-in application that handles SMS.

url: http://code.google.com/p/android-smspopup/

Standup Timer

Standup Timer is an Android application that behaves as a basic, stand-up meeting stopwatch. It can be used to ensure that your stand-up assembly completes on time, and provides each of the members the same share of time to state their progress. You can learn how to operate the timer features simply by reading through the source code. In addition this applications has clear distinction between view, model etc and has large amount of util procedures that we can reuse in our app.

url: http://github.com/jwood/standup-timer

Foursquare

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url: http://code.google.com/p/foursquared/

Pedometer

The pedometer app attempts to take the number of steps you take every day. However the count isn’t precise, you can learn different things such as interacting with accelerometer, doing voice updates, running background services etc by just studying its source code.

url: http://code.google.com/p/pedometer/

opensudoku-android

OpenSudoku is an easy open source sudoku game. You can learn the best way to show things in a grid in your view and also how to interact with a website by reading its source code.

url: http://code.google.com/p/opensudoku-android/

ConnectBot

ConnectBot is a Secure Shell client for the Android platform. You will find lot of good stuff about this app’s source code. Check it out for your self

http://code.google.com/p/connectbot/

WordPress for Android

How can a person expect a list of apps from me without mentioning WordPress This android app is from the official WordPress development team. You can learn steps to make XMLRPC calls (as well as other cool things) by reading its source code.

url: http://android.svn.wordpress.org/trunk/

If you got worthwhile open source android apps from where we could learn something, then do leave a comment and I will include them up here, If anyone interested in learning Android app programming can visit EDUmobile.ORG read more..