Android Development Tutorial

Android Development Tutorial — Building blocks of Android

Activities

Activity is the building block of the user interface. To be straight into the point, a activity is like the page in a Web app. Android supports a lot of activities. When ever a user cliks submit/login button you can bring up new activities and pressing the back button to back up, just as like as we do in a web browser.

Services

Activities are short-lived and it can be stopped or shutdown at any time.
Services, on the other hand, are designed to keep runnig, independent of any activity. One simple example for service might be checking updates to a twitter/email account.

Intents

Android Development Tutorial Eclipse Installation for Android

If you don’t have eclipse installed in your system then continue reading this post, otherwise you can skip the below steps and

Eclipse Download

There are various versions out there which one should I download ?
You can download any of the following versions.[/box]

Ok, now you have eclipse ide. Unzip the downloaded package file and run eclipse.exe

Install

The Google APIs add-on includes

First Android Program

In the New Android Project Window, we need tell eclipse a few things about our project

Now lets click Next to move to the window where we can select the target SDK.

Click Next to bring up the next window where we are going to configure our android project.

Application Name

Package Name

Android likes to keep things structured and nicely ordered. We need to give the name of the package where our project files, icon images are going to be stored.And the name you are giving here should be unique.

and the value here is the name of the activity thats going to be created by android for us.Don’t change anything for now, we can take a deep look at this later.

Minimum SDK

This field is used to specify a minimum platform version for your application

I am going to leave this field as it is for now.

As you start developing your application you will use more layout xml files. The layout xml file is like a web page where every page is unique and has its own set of components like buttons, text box, images …

Inside values directory we have strings.xml, This is where we are going to define all of our String variables.
id and value. id should be a unique one.

AndroidManifest.xml is a file which has informations about how this application should run in a device, which layout it should launch as MAIN.
What are the activities the application has, and which image it should use as icon and we can take a look closer at this in coming days.

Open main.xml from layout folder. And change the view option from Graphical Layout to coding window.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
</LinearLayout>

The value of the variable “hello” needs to be given inside the tags.

<string name="hello">Hello World, HelloWorldActivity!</string>

And finally don’t forget to put closing tag

Now I am going to create a new string variable called “welcome”.
For this I need to write the following code in strings.xml

<string name="welcome">Welcome to First Android Program</string>

Then in in main.xml, change as android:text=”@string/welcome”

Now save the changes and run the project as Android Project.

Here Android plays a smart trick to keep everything nice and clean. Whenever we create anything like string variable, color variable, a new layout, image or icon … It will store its information inside a common Resource file called R.java

Finally we came to know that the name of the xml file doesn’t do anything we can even give myStrings.xml

open R.java inside gen- your package

Three ways of creating a String

In main.xml , just enter the android:text value inside TextView, now the android will give warning to us that the string has not created. Now select the string and goto Refactor from top menu and perform Android=>Extract Android String.

Now the Extract Android String window will appear, in that you need to give the String value that you want in the String text field, and the variable id/name in the Replace by R.String text field.

Finally select the Resource file where you want to include the String, in this case strings.xml
Then press ok to create the string variable. Now the warning has gone in the main.xml and instead of “hai” you will see “@string/hai”.

Now its time to place our string at the center of the screen, for that we need to tweek main.xml

android:gravity="center"

android:layout_width="wrap_content"
android:layout_height="wrap_content"

Lets change the color of the Text and Background.

android:textColor="#ff0000"

android:background="#00ff00"

<color name="my_red">#ff0000</color>
<color name="green">#00ff00</color>

android:textcolor="@color/my_red"

<?xml version="1.0" encoding="utf-8"?>
<resources>
<color name="green">#00ff00
<color name="red">#ff0000
</resources>

Then cut and paste the color code from strings.xml to colors.xml.

<color name="red">#ff0000</color>
<color name="green">#00ff00</color>

Save Changes in both xml files.

Lets take a look at HelloWorldActivity.java in src=>package.

Finally we are going to give attention to AndroidManifest.xml

android:minSdkVersion=”15″

Inside tag we have android:icon=”@drawable/ic_launcher” this code setup the icon of the application.

android:label=”@string/app_name”

this is the application name.
If you want to change your application name then change it to any desire name you want.

activity

is used to add activity information to the Manifest file.

<activity
android:name=".HelloWorldActivity"
android:label="@string/app_name"/>

If you want to change the app name when this activity is loaded then specify the text as

android:label="@string/desire_name"

Intentfilter is used to specify the activity which should be used as the launcher of the application.

Now we are going to change the Icon of our Application.

android:icon="@drawable/logo"

You have set up everything perfectly, now its time to run our program, so save all changes and run as Android Project.You will see the following screen shot.

Complete Code

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:gravity="center"
android:background="#555555"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hai"
android:textColor="@color/red"
android:textSize="10pt"
android:textStyle="bold"
android:typeface="serif" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/welcome"
android:textSize="10pt"
android:typeface="serif"
android:textStyle="bold"
android:textColor="@color/green"/>
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello">Hello World, HelloWorldActivity!
<string name="app_name">HelloWorld
<string name="welcome">Welcome to VimalTuts
<string name="hai">Hai
</resources>

<?xml version="1.0" encoding="utf-8"?>
<resources>
<color name="green">#00ff00
<color name="red">#ff0000
</resources>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.vimaltuts.android.helloworld"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk android:minSdkVersion="15" />
<application
android:icon="@drawable/logo"
android:label="@string/app_name" >
<activity android:name=".HelloWorldActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>

package com.vimaltuts.android.helloworld;
import android.app.Activity;
import android.os.Bundle;
public class HelloWorldActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}