Thursday, 5 June 2014

Hello Word Program Using Android Programming Language

Let us start actual programming with Android Framework. Before you start writing your first example using Android SDK, you have to make sure that you have setup your Android development environment properly as explained in Android - Environment Setup tutorial. I also assume that you have a little bit working knowledge with Eclipse IDE.
So let us proceed to write a simple Android Application which will print "Hello World!".

Create Android Application

The first step is to create a simple Android Application using Eclipse IDE. Follow the option File -> New -> Project and finally select Android New Application wizard from the wizard list. Now name your application as HelloWorld using the wizard window as follows:


Next, follow the instructions provided and keep all other entries as default till the final step. Once your project is created successfully, you will have following project screen:

Anatomy of Android Application

Before you run your app, you should be aware of a few directories and files in the Android project:























S.N.Folder, File & Description
1src
This contains the .java source files for your project. By default, it includes an MainActivity.java source file having an activity class that runs when your app is launched using the app icon.
2gen
This contains the .R file, a compiler-generated file that references all the resources found in your project. You should not modify this file.
3bin
This folder contains the Android package files .apk built by the ADT during the build process and everything else needed to run an Android application.
4res/drawable-hdpi
This is a directory for drawable objects that are designed for high-density screens.
5res/layout
This is a directory for files that define your app's user interface.
6res/values
This is a directory for other various XML files that contain a collection of resources, such as strings and colors definitions.
7AndroidManifest.xml
This is the manifest file which describes the fundamental characteristics of the app and defines each of its components.
Following section will give a brief overview few of the important application files.

The Main Activity File

The main activity code is a Java file MainActivity.java. This is the actual application file which ultimately gets converted to a Dalvik executable and runs your application. Following is the default code generated by the application wizard for Hello World! application:

package com.example.helloworld;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.support.v4.app.NavUtils;

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
}
Here, R.layout.activity_main refers to the activity_main.xml file located in the res/layout folder. The onCreate() method is one of many methods that are fi red when an activity is loaded.

The Manifest File

Whatever component you develop as a part of your application, you must declare all its components in a manifest file called AndroidManifest.xml which ressides at the root of the application project directory. This file works as an interface between Android OS and your application, so if you do not declare your component in this file, then it will not be considered by the OS. For example, a default manifest file will look like as following file:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.helloworld"
   android:versionCode="1"
   android:versionName="1.0" >
   <uses-sdk
      android:minSdkVersion="8"
      android:targetSdkVersion="15" />
   <application
       android:icon="@drawable/ic_launcher"
       android:label="@string/app_name"
       android:theme="@style/AppTheme" >
       <activity
           android:name=".MainActivity"
           android:label="@string/title_activity_main" >
           <intent-filter>
               <action android:name="android.intent.action.MAIN" />
               <category android:name="android.intent.category.LAUNCHER"/>
           </intent-filter>
       </activity>
   </application>
</manifest>
Here <application>...</application> tags enclosed the components related to the application. Attribute android:icon will point to the application icon available under res/drawable-hdpi. The application uses the image named ic_launcher.png located in the drawable folders
The <activity> tag is used to specify an activity and android:name attribute specifies the fully qualified class name of the Activity subclass and the android:label attributes specifies a string to use as the label for the activity. You can specify multiple activities using <activity> tags.
The action for the intent filter is named android.intent.action.MAIN to indicate that this activity serves as the entry point for the application. The category for the intent-filter is named android.intent.category.LAUNCHER to indicate that the application can be launched from the device's launcher icon.
The @string refers to the strings.xml file explained below. Hence, @string/app_name refers to the app_name string defined in the strings.xml fi le, which is "HelloWorld". Similar way, other strings get populated in the application.
Following is the list of tags which you will use in your manifest file to specify different Android application components:
  • <activity>elements for activities
  • <service> elements for services
  • <receiver> elements for broadcast receivers
  • <provider> elements for content providers

The Strings File

The strings.xml file is located in the res/values folder and it contains all the text that your application uses. For example, the names of buttons, labels, default text, and similar types of strings go into this file. This file is responsible for their textual content. For example, a default strings file will look like as following file:
<resources>
    <string name="app_name">HelloWorld</string>
    <string name="hello_world">Hello world!</string>
    <string name="menu_settings">Settings</string>
    <string name="title_activity_main">MainActivity</string>
</resources>

The R File

The gen/com.example.helloworld/R.java file is the glue between the activity Java files like MainActivity.java and the resources like strings.xml. It is an automatically generated file and you should not modify the content of the R.java file. Following is a sample of R.java file:
/* AUTO-GENERATED FILE.  DO NOT MODIFY.
 *
 * This class was automatically generated by the
 * aapt tool from the resource data it found.  It
 * should not be modified by hand.
 */

package com.example.helloworld;

public final class R {
    public static final class attr {
    }
    public static final class dimen {
        public static final int padding_large=0x7f040002;
        public static final int padding_medium=0x7f040001;
        public static final int padding_small=0x7f040000;
    }
    public static final class drawable {
        public static final int ic_action_search=0x7f020000;
        public static final int ic_launcher=0x7f020001;
    }
    public static final class id {
        public static final int menu_settings=0x7f080000;
    }
    public static final class layout {
        public static final int activity_main=0x7f030000;
    }
    public static final class menu {
        public static final int activity_main=0x7f070000;
    }
    public static final class string {
        public static final int app_name=0x7f050000;
        public static final int hello_world=0x7f050001;
        public static final int menu_settings=0x7f050002;
        public static final int title_activity_main=0x7f050003;
    }
    public static final class style {
        public static final int AppTheme=0x7f060000;
    }
}

The Layout File

The activity_main.xml is a layout file available in res/layout directory, that is referenced by your application when building its interface. You will modify this file very frequently to change the layout of your application. For your "Hello World!" application, this file will have following content related to default layout:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent" >

   <TextView
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_centerHorizontal="true"
       android:layout_centerVertical="true"
       android:padding="@dimen/padding_medium"
       android:text="@string/hello_world"
       tools:context=".MainActivity" />

</RelativeLayout>
This is an example of simple RelativeLayout which we will study in a separate chapter. The TextView is an Android control used to build the GUI and it have various attribuites like android:layout_width, android:layout_height etc which are being used to set its width and height etc. The @string refers to the strings.xml file located in the res/values folder. Hence, @string/hello_world refers to the hello string defined in the strings.xml fi le, which is "Hello World!".

Running the Application

Let's try to run our Hello World! application we just created. I assume you had created your AVD while doing environment setup. To run the app from Eclipse, open one of your project's activity files and click Run Eclipse Run Icon icon from the toolbar. Eclipse installs the app on your AVD and starts it and if everything is fine with your setup and application, it will display following Emulator window:


 Congratulations!!! you have developed your first Android Application and now just keep following rest of the tutorial step by step to become a great Android Developer. All the very best.

Wednesday, 4 June 2014

Application Components Of Android Programming Language

Application components are the essential building blocks of an Android application. These components are loosely coupled by the application manifest file AndroidManifest.xml that describes each component of the application and how they interact.
There are following four main components that can be used within an Android application:

ComponentsDescription
Activities           They dictate the UI and handle the user interaction to the smartphone screen
Services            They handle background processing associated with an application.
Broadcast Receivers  They handle communication between Android OS and applications.
Content Providers   They handle data and database management issues.



Activities

An activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. If an application has more than one activity, then one of them should be marked as the activity that is presented when the application is launched.
An activity is implemented as a subclass of Activity class as follows:

public class MainActivity extends Activity {

}

Services

A service is a component that runs in the background to perform long-running operations. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity.
A service is implemented as a subclass of Service class as follows:
public class MyService extends Service {

} 

Broadcast Receivers

Broadcast Receivers simply respond to broadcast messages from other applications or from the system. For example, applications can also initiate broadcasts to let other applications know that some data has been downloaded to the device and is available for them to use, so this is broadcast receiver who will intercept this communication and will initiate appropriate action.
A broadcast receiver is implemented as a subclass of BroadcastReceiver class and each message is broadcasted as an Intent object.

public class MyReceiver extends BroadcastReceiver {  

}

Content Providers

A content provider component supplies data from one application to others on request. Such requests are handled by the methods of the ContentResolver class. The data may be stored in the file system, the database or somewhere else entirely.
A content provider is implemented as a subclass of ContentProvider class and must implement a standard set of APIs that enable other applications to perform transactions.

public class MyContentProvider extends ContentProvider {  
 }

Additional Components

There are additional components which will be used in the construction of above mentioned entities, their logic, and wiring between them. These components are:
ComponentsDescription
FragmentsRepresents a behavior or a portion of user interface in an Activity.
ViewsUI elements that are drawn onscreen including buttons, lists forms etc.
LayoutsView hierarchies that control screen format and appearance of the views.
IntentsMessages wiring components together.
ResourcesExternal elements, such as strings, constants and drawables pictures.
ManifestConfiguration file for the application.
 


Architecture Of Android Programming Language

Android operating system is a stack of software components which is roughly divided into five sections and four main layers as shown below in the architecture diagram.


Linux kernel

At the bottom of the layers is Linux - Linux 2.6 with approximately 115 patches. This provides basic system functionality like process management, memory management, device management like camera, keypad, display etc. Also, the kernel handles all the things that Linux is really good at such as networking and a vast array of device drivers, which take the pain out of interfacing to peripheral hardware.

Libraries

On top of Linux kernel there is a set of libraries including open-source Web browser engine WebKit, well known library libc, SQLite database which is a useful repository for storage and sharing of application data, libraries to play and record audio and video, SSL libraries responsible for Internet security etc.

Android Runtime

This is the third section of the architecture and available on the second layer from the bottom. This section provides a key component called Dalvik Virtual Machine which is a kind of Java Virtual Machine specially designed and optimized for Android.
The Dalvik VM makes use of Linux core features like memory management and multi-threading, which is intrinsic in the Java language. The Dalvik VM enables every Android application to run in its own process, with its own instance of the Dalvik virtual machine.
The Android runtime also provides a set of core libraries which enable Android application developers to write Android applications using standard Java programming language.

Application Framework

The Application Framework layer provides many higher-level services to applications in the form of Java classes. Application developers are allowed to make use of these services in their applications.

Applications

You will find all the Android application at the top layer. You will write your application to be installed on this layer only. Examples of such applications are Contacts Books, Browser, Games etc.

Tuesday, 3 June 2014

Android Environment Setup

You will be glad to know that you can start your Android application development on either of the following operating systems:

  • Microsoft Windows XP or later version.
  • Mac OS X 10.5.8 or later version with Intel chip.
  • Linux including GNU C Library 2.7 or later.
Second point is that all the required tools to develop Android applications are freely available and can be downloaded from the Web. Following is the list of software's you will need before you start your Android application programming.

  • Java JDK5 or JDK6
  • Android SDK
  • Eclipse IDE for Java Developers (optional)
  • Android Development Tools (ADT) Eclipse Plugin (optional)
Here last two components are optional and if you are working on Windows machine then these components make your life easy while doing Java based application development. So let us have a look how to proceed to set required environment.

Step 1 - Setup Java Development Kit (JDK)


You can download the latest version of Java JDK from Oracle's Java site: Java SE Downloads. You will find instructions for installing JDK in downloaded files, follow the given instructions to install and configure the setup. Finally set PATH and JAVA_HOME environment variables to refer to the directory that contains java and javac, typically java_install_dir/bin and java_install_dir respectively.

If you are running Windows and installed the JDK in C:\jdk1.6.0_15, you would have to put the following line in your C:\autoexec.bat file.

set PATH=C:\jdk1.6.0_15\bin;%PATH%
set JAVA_HOME=C:\jdk1.6.0_15
 
Alternatively, you could also right-click on My Computer, select Properties, then Advanced, then Environment Variables. Then, you would update the PATH value and press the OK button.
On Linux, if the SDK is installed in /usr/local/jdk1.6.0_15 and you use the C shell, you would put the following code into your .cshrc file.

setenv PATH /usr/local/jdk1.6.0_15/bin:$PATH
setenv JAVA_HOME /usr/local/jdk1.6.0_15

  Alternatively, if you use an Integrated Development Environment (IDE) Eclipse, then it will know automatically where you have installed your Java.

Step 2 - Setup Android SDK

You can download the latest version of Android SDK from Android official website : Android SDK Downloads. If you are installing SDK on Windows machine, then you will find a installer_rXX-windows.exe, so just download and run this exe which will launch Android SDK Tool Setup wizard to guide you throughout of the installation, so just follow the instructions carefully. Finally you will have Android SDK Tools installed on your machine.
If you are installing SDK either on Mac OS or Linux, check the instructions provided along with the downloaded android-sdk_rXX-macosx.zip file for Mac OS and android-sdk_rXX-linux.tgz file for Linux. This tutorial will consider that you are going to setup your environment on Windows machine having Windows 7 operating system.
So let's launch Android SDK Manager using the option All Programs > Android SDK Tools > SDK Manager, this will give you following window:

Once you launched SDK manager, its time to install other required packages. By default it will list down total 7 packages to be installed, but I will suggest to de-select Documentation for Android SDK and Samples for SDK packages to reduce installation time. Next click Install 7 Packages button to proceed, which will display following dialogue box:

  


If you agree to install all the packages, select Accept All radio button and proceed by clicking Install button. Now let SDK manager do its work and you go, pick up a cup of coffee and wait until all the packages are installed. It may take some time depending on your internet connection. Once all the packages are installed, you can close SDK manager using top-right cross button.

Step 3 - Setup Eclipse IDE

All the examples in this tutorial have been written using Eclipse IDE. So I would suggest you should have latest version of Eclipse installed on your machine.
To install Eclipse IDE, download the latest Eclipse binaries from http://www.eclipse.org/downloads/. Once you downloaded the installation, unpack the binary distribution into a convenient location. For example in C:\eclipse on windows, or /usr/local/eclipse on Linux and finally set PATH variable appropriately.
Eclipse can be started by executing the following commands on windows machine, or you can simply double click on eclipse.exe

%C:\eclipse\eclipse.exe
 Eclipse can be started by executing the following commands on Linux machine:
$/usr/local/eclipse/eclipse 
 After a successful startup, if everything is fine then it should display following result:

Step 4 - Setup Android Development Tools (ADT) Plugin

This step will help you in setting Android Development Tool plugin for Eclipse. Let's start with launching Eclipse and then, choose Help > Software Updates > Install New Software. This will display the following dialogue box.

Now use Add button to add ADT Plugin as name and https://dl-ssl.google.com/android/eclipse/ as the location. Then click OK to add this location, as soon as you will click OK button to add this location, Eclipse starts searching for the plug-in available the given location and finally lists down the found plugins.

Now select all the listed plug-ins using Select All button and click Next button which will guide you ahead to install Android Development Tools and other required plugins.

Step 5 - Create Android Virtual Device

To test your Android applications you will need a virtual Android device. So before we start writing our code, let us create an Android virtual device. Launch Android AVD Manager using Eclipse menu options Window > AVD Manager> which will launch Android AVD Manager. Use New button to create a new Android Virtual Device and enter the following information, before clicking Create AVD button.

 If your AVD is created successfully it means your environment is ready for Android application development. If you like, you can close this window using top-right cross button. Better you re-start your machine and once you are done with this last step, you are ready to proceed for your first Android example but before that we will see few more important concepts related to Android Application Development.

Application of Android Programming Language

  • Android applications are usually developed in the Java language using the Android Software Development Kit.
  • Once developed, Android applications can be packaged easily and sold out either through a store such as Google Play or the Amazon Appstore.
  • Android powers hundreds of millions of mobile devices in more than 190 countries around the world. It's the largest installed base of any mobile platform and growing fast. Every day more than 1 million new Android devices are activated worldwide.
  • This tutorial has been written with an aim to teach you how to develop and package Android application. We will start from environment setup for Android application programming and then drill down to look into various aspects of Android applications.

Features Of Android Programming Language.

  1. Beautiful UI
  2. Connectivity
  3. Storage
  4. Media Support
  5. Messaging
  6. Web Browser
  7. Multitouch
  8. Multi-Tasking
  9. Resizable Widgets
  10. Multi Language
  11. GCM
  12. Wifi - Direct
  13. Android Beam

What is Android ???

  • Android is an open source and Linux-based Operating System for mobile devices such as smartphones and tablet computers. Android was developed by the Open Handset Alliance, led by Google, and other companies.
  • Android offers a unified approach to application development for mobile devices which means developers need only develop for Android, and their applications should be able to run on different devices powered by Android.
  • The first beta version of the Android Software Development Kit (SDK) was released by Google in 2007 where as the first commercial version, Android 1.0, was released in September 2008.
  • On June 27, 2012, at the Google I/O conference, Google announced the next Android version, 4.1 Jelly Bean.

Basic Of Android Programming Language

  • Android is an open source and Linux Based Operating System for mobile devices such as Smartphones and talbets computers.
  • Android was developed by the Open Handset Alliance led by Google and other companies.
  • Android Programming based on the Java Programming Language. So if you have basic understanding on Java Programming then it will be a fun to learn Android Application Development 

  Android Profile

  1. Company/Developer :  Google Open Handset Alliance
  2. Written-in : C(core), C++, Java(UI)
  3. OS-Family : Unix-Like
  4. Initial Release : 23,September,2008
  5. Marketing Target : Smartphones, Tablet Computers
  6. Avialable in : Multi-Lingual (46 Languages)
  7. Package Manager : Google Play, APK
  8. Supported Platform : 32-bit ARM, MIPS, x86
  9. Kernel Type : Monolithic (modified linux kernel)
 
  • Android is an Operating System based on the Linux Kernel with a User Interface based on direct Manipulation, designed primarily for touch screen mobile device using touch input that loosely correspood to real world actions, like swiping, tapping, pinching, and reverse pinching to manipulate on screen object and a virtual keyboard

Followers