How to create android applications?


Hello readers, welcome back!! I was running out of topics to scribble something in my blog. Finally one question which I used to ask from some months came to my mind “How these guys are making excellent applications (some of them are even free) for smartphones?” This article is to throw some light in the area of developing android applications.

 I have given an introduction about android in my previous blog Something aboutAndroid. Now, lets move on to something bigger

Introduction

Developers can create apps for the Android platform using the Android SDK.

Java is the major programming language for developing apps and it runs on Dalvik, a custom virtual machine designed for embedded systems:-runs on the top of Linux kernel. The application framework is very powerful and does most of the stuffs for the developers: - access device hardware, access location information, run background services, set alarms, notifications in status bar etc.

Every app runs on its own process with its own instance of DVM, which executes the file in Dalvik executable format (.dex). Dalvik has the capability to enable single device to run multiple VM (Virtual Machine) efficiently.

DVM = Register based à runs classes complied by JLM à transformed into .dex format using DX Tool

So, what about the .Net developers? Do they have to learn Java to create android app? Though, the core concept of c# and Java is the same, it’s not an easy job for .Net developers. Yeah, I know that..!!! Here’s the happy news

Though Java is the underlying code for Android OS, one company called XMarian became the game changer ripping out most of the java with c#. 

Xmarian has created platform called Mono allowing Android and iOS apps to be developed using c#, which runs on the top of Java. They have 2 major products MonoTouch – for iOS and MonoDroid – for Android.

Also company’s recent project - “XobotOS Research Project” shows the capability to remove java layer via “machine translation of Android from Java to C#”. In this project, more than million lines of Java code was converted to C# using tool called Sharpen.   

1st Android application

So, that was some theory about android app and its time to create one. Whenever we learn a new language, we always create “Hello World!” no matter Web, Windows applications.

a) In Java

Steps to create Hello World in java is given below

Language - Java should be installed in the PC

IDE - Install Eclipse IDE, which will make the development easy since it has great plug-in for project creation and management (Development can also be done using command-line without Eclipse)


Platform – At least one Android platform need to be installed in the SDK environment

AVD – Create an AVD (Audio Virtual Device), which defines the system image and device settings used by the Android Emulator (to run the applications)

Project – Create android project in Eclipse; - there are some basic properties in this step such as Build Target (to choose Android version), project name, package name etc.

Code – write the code: - one important class is Activity which can run and do work.

UI - Create the android user interface, composed of hierarchies of objects called “Views”. View is a drawing object used in UI layout such as button, image, label etc. Android provides an option to create alternate UI construction model – XML based layout files, to avoid changing source code for small UI changes.

Structure of XML = Tree of XML elements à each node is the name of View class

Run – Once the code is compiled run the app using Emulator that creates run configuration and launches the Android Emulator

Output – The extension of android application is .apk. In-fact this is a zip file disguised as an .apk. If we change the extension and un-zip, we can see a file named classes.dex, the most important file containing encrypted java files.

We can’t directly convert a jar file to an apk since it has to be compiled for Android. Eclipse IDE makes this job easier for us to create signed apk from java code.

b) In .Net

Steps to create Hello World in .Net is given below

Language – Install .Net Framework 4.0

IDE – Visual Studio 2010 is the best IDE available for creating .Net applications. We also need a plug-in “Mono for Android or MonoDroid” for creating Android apps.
Mono is an open source implementation of the .NET Framework based on the C# programming language and the Common Language Runtime (CLR). Mono tools make it possible for .NET developers to use their existing code, libraries, tools, and C# skills to build mobile apps for devices running Apple's iOS and Google's Android.

Project – Mono gives various options for creating new application – Library project, Android application, and OpenGL (Open graphics library for 2D and 3D graphics) application

Code – Similar to Java, Activity class is used in c# too, and this will be created on project creation

UI – Create the user interface for Android. XML based UI system (XAML and HTML) can be used to replace hard coded strings. The auto-generated Resource class is in the Resource.designer.cs and this should not be edited.

Emulator – MonoDevelop is the emulator used by Monodroid. We should choose a device on running the emulator

Deploy & Launch – Monodroid deploys the app to the emulator and then launches it.



Hands on with Eclipse

The detailed steps to develop apps using eclipse is given below

1) Install JDK – this is freely available in Java / Oracle web site

2) Install Android SDK Kit – free download from http://developer.android.com

3) Run Android SDK – You need to install the required Android packages and resources online (for each version such as 2.2, 2.3, 4.0 etc)

4) Install Eclipse for Java

5) Install the ADT plug in to create Android project in eclipse – you cannot create new android project without this

6) Run AVD Manager (this comes along with SDK) – Create virtual device bases on the android version and target device

7) Run Eclipse – Create new Android project – do some coding (many examples available online)

8) Compile and test it in AVD Manager

Conclusion

I hope my article has given some basics idea to .Net and Java developers who want to start developing android apps. The examples mentioned in the article are to create stand alone applications similar to windows apps.
What about web applications? While designing web applications don’t we have to think about smartphones? Hmm, may be next article!!! 

 If you like the article, post your comments and keep reading!!! Thanks ..See you later!!!

Resources

Creating apps in .Net - http://docs.xamarin.com/android

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