Getting started with Android

Posted by Abdul | Tue, 14 Jun 2011 | Tagged: java, mobile, android, tutorial

Android is a open source operating system designed specifically for mobile platforms. Over the last few years Android is taking over the mobile market drastically. This article shows how to get started with Android.

Setting up the Work Environment

Eclipse IDE is more suitable environment for developing Android applications.

Things to be downloaded:

Latest Eclipse IDE
ADT plugin
Android SDK

Complete steps for setting up working environment is given in http://developer.android.com/sdk/index.html

Steps to Create Android Virtual Device

Android Virtual Device (AVD) is an mobile phone emulator, where you can test your Android application. The steps create and start the AVD is given below.

Start Eclipse IDE.
Open your Android SDK and AVD manager.
Click New button to create new virtual device.
Provide the device name and select the appropriate API level suitable for your application.
Provide the appropriate SD card size.
Click the Create AVD button.
Select the virtual device you have created before and click start button.

Figure 1. Android Virtual Device

Starting New Project

Start Eclipse IDE, if not already started.
Click File -> New -> Android project
Enter the project name
Select the API level same as your Virtual device API level
Enter the application name and package name. Package name should start with "com."
Enter the Activity name and SDK version number
Click the finish button.

Example:

Project Name	hello
API Level	2.2(8)
Application Name	Hello Android
Activity Name	Hello
SDK version	8

Directory Structure of a New Project

src - This folder contains your Java class files. Class files generally extend the Activity class.
gen - This folder contains an automatically generated Java file called R.java. This Java file has references for all your resourses. Eg. GUI layout XML files, image files, media files, etc.
res - This folder contain all your resourses.
- drawable - contains image files
- layout - contains GUI layout xml files
- values - contains all your text or string used in your GUI layout
AndroidManifest.xml - This file contains list of Activity classes and permissions to access the hardware.

Hello World

The Hello World application gets the user name as input and prints a hello world message to the user. This example demonstrates the TextView, EditText and Button widgets. Create a new project using the steps explained above.

Creating GUI Layout

We can design our GUI layout either using drag and drop method or we can directly edit the XML file. Open the main.xml file under layout folder and replace the text with the below content.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView
        android:text="Enter your name:"
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        </TextView>
    <EditText
        android:layout_width="match_parent"
        android:id="@+id/editText1"
        android:layout_height="wrap_content"
        android:text="">
        </EditText>
    <LinearLayout
    android:layout_width="match_parent"
    android:id="@+id/linearLayout1"
    android:layout_height="wrap_content">
        <Button
                android:text="SHOW"
                android:id="@+id/button1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content">
                </Button>
        <Button
                android:text="CLEAR"
                android:id="@+id/button2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content">
                </Button>
    </LinearLayout>
    <TextView
        android:text="Welcome Message:"
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        </TextView>
</LinearLayout>

In the above XML file we have used the linear layout to place widgets. In this example we used two TextView widgets, two Button widgets and one EditText. Buttons were placed inside another linear layout for proper alignment.

Open your Java file present in the src folder and replace the text with below content.

package com.hello;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class Hello extends Activity {

    EditText name;
    Button showButton;
    Button clearButton;
    TextView hello;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main); /*  */

        name = (EditText) findViewById(R.id.editText1); /*  */
        hello = (TextView) findViewById(R.id.textView2);

        showButton = (Button) findViewById(R.id.button1);
        clearButton = (Button) findViewById(R.id.button2);

        showButton.setOnClickListener(new OnClickListener() { /*  */
                public void onClick(View v) {
                    hello.append("\n\n"+"Hello! "+name.getText().toString());
                }
            });

        clearButton.setOnClickListener(new OnClickListener() {
                public void onClick(View v) {
                    name.setText("");
                    hello.setText("");
                    hello.setText("Welcome Message:");
                }
            });
    }
}

	The `setContentView()` method is used specify which GUI layout is to be used. Here we select the GUI layout `main.xml`. The generated `R` class contains a ID which refers to the GUI layout.
	The `findViewById()` method is used to get a reference to widget. Here again we use an ID in the `R` class which refers to the widget.
	A click event listener is registered on the `showButton` and the `clearButton`.

Running Your Application

A Run Configuration binds an activity in a project and an Android Virtual Device. The procedure to create a Run Configuration is given below. Once a Run Configuration is created, successive runs can reuse the previously created configuration.

In the Eclipse IDE, select the menu item Run -> Run Configuration ...

Figure 2. Creating a Run Configuration
In the Run Configuration ... dialog, select Android Application.
Click on New.
Enter a configuration name of your project - hello.
Choose your project folder hello.
Select the activity to be launched com.hello.Hello.

Figure 3. Creating a Run Configuration
Ensure Deployment Target Selection Mode is Automatic. This will cause the activity to be launched in an AVD, with a matching Platform and API level.
Click on Run.

Figure 4. Hello World in Action