Learn Andriod Development Completely With in 30 Minutes Part1

Android Application:


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.

Environment Setup:

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

  1. Microsoft Windows XP or later version.
  2. Mac OS X 10.5.8 or later version with Intel chip.
  3. Linux including GNU C Library 2.7 or later.

The 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.
1.Java JDK5 or JDK6,Android SDK
2.Eclipse IDE for Java Developers (optional)
3.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.

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

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 an 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 set up 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.


Step 3 - Setup Eclipse IDE:




All the examples in this tutorial have been written using Eclipse IDE. So I would suggest you should have the 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 start up, 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 Plug in 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 at the given location and finally lists the found plug ins.






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 the 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 Components
Application components are the essential building blocks of an Android application. These components are loosely coupled by the application manifest file Android Manifest.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
1. Activities:
  An activity is implemented as a subclass of Activity class as follows:
           public class Main Activity extends Activity {
                   }
2.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 My Service 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 Broadcast Receiver class and each message is broad casted as an Intent object.
           public class My Receiver    extends    Broadcast Receiver {
                    }
Content Providers:
A content provider component supplies data from one application to others on request. Such requests are handled by the methods of the Content Resolver 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 Content Provider class and must implement a standard set of APIs that enable other applications to perform transactions
  public class My ContentProvider extends    ContentProvider 
                 { 
                   }
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.





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



  1. Src: 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. 
  2. Gen:This contains the .R file, a compiler-generated file that references all the resources found in your project. You should not modify this file.
     
  3. Bin:This folder contains the Android package files .apk built by the ADT during the build process and everything
  4. res/drawable-hdpi:This is a directory for drawable objects that are designed for high-density screens.res/layout This is a directory for files that define your app's user interface. 
  5. res/values:This is a directory for other various XML files that contain a collection of resources, such as strings and colors definitions. 
  6. AndroidManifest.xml: This is the manifest file which describes the fundamental characteristics of the app and defines each of its components.
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;
            }
            }

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. Attributeandroid: the 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 specify 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 theapp_name string defined in the strings.xml file, 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:
  1. <activity>elements for activities                                                 
  2. <service> elements for services
  3. <receiver> elements for broadcast receivers
  4. <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 the 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 likeMainActivity.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" >

<TextViewandroid: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 has various attributes 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 file, which is "Hello World!".

Running the Application:

Let's try to run our Hello World! the 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 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.




                                                                                                                   



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