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Basics of Android

Basics of Android

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Android Tutorial

Android is a complete set of software for mobile devices such as tablet computers, smartphones, electronic book readers, notebooks, set-top boxes etc. It contains anlinux based operating system, middleware and key mobile applications.
It can be thought of as a mobile operating system. But it is not limited to mobile only. It is currently used in mobiles, tablets, televisions etc.
This tutorial is developed for beginners and experienced persons. Let's see the topics of android that we are going to learn.
Basics of Android
In this fundamental chapter, you will learn about android, its components, how to create first android application, internal of first android application etc.

 

Activity and Intent
It provides the detail of activity, its life cycle with example, implicit intent, sending information from one activity to another etc.

Android UI Widgets
There are given a lot of android ui widgets examples such as toggle button, alert dialog, spinner, progress bar, alert dialog etc.

Menus in Android
Here, you will learn about the option menu that is primary menu, context menu that works on long press and popup menu.

Service in Android
It can be used to perform any task in background. It doesn't have any UI.

Data Storage
You can store data in android using preferences, internal storage, external storage and sqlite database. Preferences are used to primitives, internal storage stores data in device internal memory, external storage stores data in device external memory such as SD card and SQLite is used to store data in sqlite database i.e. inbuilt in android OS.

SQLite Database

XML and JSON Parsing
There are three ways to parse the xml file but android recommends XMLPullParser to parse the XML. Instead of XML, JSON is prefered currently because it is short and fast.

Android Multimedia
Android multimedia api deals in playing and controlling the audio and video.

Android Speech API
Speech API is used to convert text into speech.

Telephony API
It can be used to get details about the device, making phone calls, sending sms, sending emails etc.
Device Connectivity
We can connect and control bluetooth, wifi and camera in android.






Android - What, Where and Why?


Android is a software package and linux based operating system for mobile devices such as tablet computers and smartphones.
It is developed by Google and later the OHA (Open Handset Alliance). Java language is mainly used to write the android code even though other languages can be used.
The goal of android project is to create a successful real-world product that improves the mobile experience for end users.

What is Open Handset Alliance (OHA) ?


It's a consortium of 84 companies such as google, samsung, AKM, synaptics, KDDI, Garmin, Teleca, Ebay, Intel etc.
It was established on 5th November, 2007, led by Google. It is commited to advance open standards, provide services and deploy handsets using the Android Plateform.

Features of Android

There are many advantages of android. They are as follows:
  • It is open-source.
  • Anyone can customize the Android Platform.
  • There are a lot of mobile applications that can be choosen by the consumer.
  • It provides many interesting features like weather details, opening screen, live RSS (Really Simple Syndication) feeds etc.
  • It provides support for messaging services(SMS and MMS), web browser, storage (SQLite), connectivity (GSM, CDMA, Blue Tooth, Wi-Fi etc.), media, handset layout etc.

Categories of Android applications


There are many android applications in the market. The top categories are:
  • Entertainment
  • Tools
  • Communication
  • Productivity
  • Personalization
  • Music and Audio
  • Social
  • Media and Video
  • Travel and Local etc.


Android - History and Versions

Android History and Versions are interesting. The codenames of android ranges from A to J currently, such as Aestro, Blender, Cupcake, Donut, Eclair, Froyo, Gingerbread, Honeycomb, Ice Cream Sandwitchand Jelly Bean,KitKat and Marshmallow. Let's see the main points of android history:
  • Initially, Andy Rubin founded Android Incorporation in Palo Alto, California, United States in October, 2003.
  • In August 17, 2005, Google acquired Android Inc. Since then, it is in the subsidiary of Google Inc.
  • Key employees of Android Inc. are Andy Rubin, Rich Miner, Nick Sears and Chris White.

Android Versions, Codename and API

Let's see the android versions codename and API provided by Google.
Version
Codename
API
1.5
Cupcake
3
1.6
Donut
4
2.1
Éclair
7
2.2
Froyo
8
2.3
Gingerbread
9 and 10
3.1 and 3.3
Honeycomb
12 and 13
4.0
Ice Cream Sandwitch
15
4.1 and 4.2
Jelly Bean
16 and 17

Android Versions Image













Android Software Stack

Android software stack (also known as android architecture) includes linux kernal, native libraries (middleware), Android Runtime, Application Framework and Applications.

Linux Kernal is responsible for device drivers, power management, resource access etc. OS tasks.
On the top of linux kernal, their are Native libraries such as WebKit, OpenGL, FreeType, SQLite, Media, C runtime library (libc) etc.
The WebKit library is responsible for browser support, SQLite is for database, FreeType for font support, Media for playing and recording audio and video formats.
The main Android API's are UI (User Interface), telephony, resources, locations, Content Providers (data) and package managers.





Android Core Building Blocks


A component is simply a piece of code that has a well defined life cycle e.g. Activity, Receiver, Service etc.
The core building blocks or fundamental components of android are activities, views, intents, services, content providers, fragments and AndroidManifest.xml.

Activity

An activity is a class that represents a single screen. It is like a Frame in AWT.

View

A view is the UI element such as button, label, text field etc. Anything that you see is a view.

Intent

Intent is used to invoke components. It is mainly used to:
  • Start the service
  • Launch an activity
  • Display a web page
  • Display a list of contacts
  • Broadcast a message
  • Dial a phone call etc.
For example, you may write the following code to view the webpage.
Intent intent=new Intent(Intent.ACTION_VIEW);
intent.setData(Uri.parse("http://www.google.com"));
startActivity(intent);

Service

Service is a background process that can run for a long time.
There are two types of services local and remote. Local service is accessed from within the application whereas remote service is accessed remotely from other applications running on the same device.

Content Provider

Content Providers are used to share data between the applications.

Fragment

Fragments are like parts of activity. An activity can display one or more fragments on the screen at the same time.

AndroidManifest.xml

It contains informations about acvities, content providers, permissions etc. It is like the web.xml file in Java EE.

Android Virtual Device (AVD)

It is used to test the android application without the need for mobile or tablet etc. It can be created in different configurations to emulate different types of real devices.





Android Emulator

Android Emulator is used to run, debug and test the android application. If you don't have the real device, it can be the best way to run, debug and test the application.
It uses an open source processor emulator technology called QEMU.
The emulator tool enables you to start the emulator from the command line. You need to write:
emulator -avd <AVD NAME>
In case of Eclipse IDE, you can create AVD by Window menu > AVD Manager > New.
In the given image, you can see the android emulator, it displays the output of the hello android example.





Installing softwares for Android

Android supports java, c++, c# etc. language to develop android applications. Java is the officially supported language for android. All the android examples of this site is developed using Java language and Eclipse IDE.
Here, we are going to tell you, the required softwares to develop android applications using Eclipse IDE.

Simple way by ADT Bundle

It is the simplest technique to install required softwares for android application. It includes:
  • Eclipse IDE
  • Android SDK
  • Eclipse Plugin
If you download the ADT from android site, you don't need to have eclipse IDE, android SDK and eclipse Plugin because it is already included in adt bundle.
If you have downloaded the ADT bundle, unjar it, go to eclipse IDE and start the eclipse by clicking on the eclipse icon. You don't need to do any extra steps here.

If eclipse is not started, paste the JRE directory inside the eclipse directory.

Other way by setting up eclipse IDE manually





How to setup Android for Eclipse IDE

In this page, you will learn what softwares are required for running an android application on eclipse IDE. Here, you will be able to learn how to install the android SDK ADT plugin for Eclipse IDE. Let's see the softwares required to setup android for eclipse IDE manually.
1.    Install the JDK
2.    Download and install the Eclipse for developing android application
3.    Download and Install the android SDK
4.    Intall the ADT plugin for eclipse
5.    Configure the ADT plugin
6.    Create the AVD
7.    Create the hello android application

1) Install the Java Development Kit (JDK)

For creating android application, JDK must be installed if you are developing the android application with Java language. download the JDK

2) Download and install the Eclipse IDE for developing the android application

For developing the android application using eclipse IDE, you need to install the Eclipse. you can download it from this location download the Eclipse. Eclispe classic version is recommended but we are using the Eclipse IDE for JavaEE Developers (Eclipse Helios).

3) Download and install the android SDK

First of all, download the android SDK. In this example we have installed the android SDK for windows (.exe version). Now double click on the exe file, it will be installed. I am using the android 2.2 version here.

4) Download the ADT plugin for eclipse

ADT (Android Development Tools) is required for developing the android application in the eclipse IDE. It is the plugin for Eclipse IDE that is designed to provide the integrated environment.
For downloading the ADT, you need to follow these steps:
1.    Start the eclipse IDE, then select Help > Install new software...
2.    In the work with combo box, write https://dl-ssl.google.com/android/eclipse/ 


 
3.    select the checkbox next to Developer Tools and click next
4.    you will see, a list of tools to be downloaded here, click next
5.    click finish
6.    After completing the installation, restart the eclipse IDE

5) Configuring the ADT plugin

After the installing ADT plugin, now tell the eclipse IDE for your android SDK location. For this:
1.    Select the Window menu > preferences
2.    Now select the android from the left panel. Here you may see a dialog box asking if you want to send the statistics to the google. Click proceed.
3.    Click on the browse button and locate your SDK directory e.g. my SDK location is C:\Program Files\Android\android-sdk .
4.    Click the apply button then OK.

6) Create an Android Virtual Device (AVD)

For running the android application in the Android Emulator, you need to create and AVD. For creating the AVD:
1.    Select the Window menu > AVD Manager
2.    Click on the new button, to create the AVD
3.    Now a dialog appears, write the AVD name e.g. myavd. Now choose the target android version e.g. android2.2.
4.    click the create AVD

7) create and run the simple android example





Hello Android Example

In this page, you will know how to create the simple hello android application. We are creating the simple example of android using the Eclipse IDE. For creating the simple example:
1.    Create the new android project
2.    Write the message (optional)
3.    Run the android application

Example of Hello Android

You need to follow the 3 steps mentioned above for creating the Hello android application.

1) Create the New Android project

For creating the new android project:
1.    Select File > New > Project...
2.    Select the android project and click next
3.    Fill the Details in this diaglog box and click finish

Now an android project have been created. You can explore the android project and see the simple program, it looks like: 

2) Write the message

For writing the message we are using the TextView class. Change the onCreate method as:
 
package com.example.helloandroid;
 
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;
 
public class MainActivity extends Activity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        TextView textview=new TextView(this);
        textview.setText("Hello Android!");
        
        setContentView(textview);
    }
 
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
    
}
 

To understand the first android application, visit the next page (internal details of hello android example).

3) Run the android application

To run the android application:
·        Right click on your project > Run As.. > Android Application
The android emulator might take 2 or 3 minutes to boot. So please have patience. After booting the emulator, the eclipse plugin installs the application and launches the activity. You will see something like this:






Internal Details of Hello Android Example


Here, we are going to learn the details of first android program.
Android application contains different components such as java source code, string resources, images, manifest file, apk file etc. Let's understand the project structure of android application.

Java Source Code

Let's see the java source file created by the Eclipse IDE:
File: MainActivity.java
1.    package com.example.helloandroid;  
2.      
3.    import android.os.Bundle;  
4.    import android.app.Activity;  
5.    import android.view.Menu;  
6.    import android.widget.TextView;  
7.      
8.    public class MainActivity extends Activity {//(1)  
9.      
10.     @Override  
11.     protected void onCreate(Bundle savedInstanceState) {//(2)  
12.         super.onCreate(savedInstanceState);  
13.                 
14.         setContentView(R.layout.activity_main);//(3)  
15.     }  
16.   
17.     @Override  
18.     public boolean onCreateOptionsMenu(Menu menu) {//(4)  
19.         // Inflate the menu; this adds items to the action bar if it is present.  
20.         getMenuInflater().inflate(R.menu.activity_main, menu);  
21.         return true;  
22.     }  
23.       
24. }  
(1) Activity is a java class that creates and default window on the screen where we can place different components such as Button, EditText, TextView, Spinner etc. It is like the Frame of Java AWT.
It provides life cycle methods for activity such as onCreate, onStop, OnResume etc.
(2) The onCreate method is called when Activity class is first created.
(3) The setContentView(R.layout.activity_main) gives information about our layout resource. Here, our layout resources are defined in activity_main.xml file.
File: activity_main.xml
1.    <RelativeLayout xmlns:androclass="http://schemas.android.com/apk/res/android"  
2.        xmlns:tools="http://schemas.android.com/tools"  
3.        android:layout_width="match_parent"  
4.        android:layout_height="match_parent"  
5.        tools:context=".MainActivity" >  
6.      
7.        <TextView  
8.            android:layout_width="wrap_content"  
9.            android:layout_height="wrap_content"  
10.         android:layout_centerHorizontal="true"  
11.         android:layout_centerVertical="true"  
12.         android:text="@string/hello_world" />  
13.   
14. </RelativeLayout>  
As you can see, a textview is created by the framework automatically. But the message for this string is defined in the strings.xml file. The @string/hello_world provides information about the textview message. The value of the attribute hello_world is defined in the strings.xml file.
File: strings.xml
1.    <?xml version="1.0" encoding="utf-8"?>  
2.    <resources>  
3.      
4.        <string name="app_name">helloandroid</string>  
5.        <string name="hello_world">Hello world!</string>  
6.        <string name="menu_settings">Settings</string>  
7.      
8.    </resources>  
You can change the value of the hello_world attribute from this file.

Generated R.java file

It is the auto-generated file that contains IDs for all the resources of res directory. It is generated by aapt(Android Asset Packaging Tool). Whenever you create any component on activity_main, a corresponding ID is created in the R.java file which can be used in the Java Source file later.
File: R.java
1.    /* AUTO-GENERATED FILE.  DO NOT MODIFY. 
2.     * 
3.     * This class was automatically generated by the 
4.     * aapt tool from the resource data it found.  It 
5.     * should not be modified by hand. 
6.     */  
7.      
8.    package com.example.helloandroid;  
9.      
10. public final class R {  
11.     public static final class attr {  
12.     }  
13.     public static final class drawable {  
14.         public static final int ic_launcher=0x7f020000;  
15.     }  
16.     public static final class id {  
17.         public static final int menu_settings=0x7f070000;  
18.     }  
19.     public static final class layout {  
20.         public static final int activity_main=0x7f030000;  
21.     }  
22.     public static final class menu {  
23.         public static final int activity_main=0x7f060000;  
24.     }  
25.     public static final class string {  
26.         public static final int app_name=0x7f040000;  
27.         public static final int hello_world=0x7f040001;  
28.         public static final int menu_settings=0x7f040002;  
29.     }  
30.     public static final class style {  
31.         /**  
32.         Base application theme, dependent on API level. This theme is replaced 
33.         by AppBaseTheme from res/values-vXX/styles.xml on newer devices. 
34.      
35.  
36.             Theme customizations available in newer API levels can go in 
37.             res/values-vXX/styles.xml, while customizations related to 
38.             backward-compatibility can go here. 
39.          
40.  
41.         Base application theme for API 11+. This theme completely replaces 
42.         AppBaseTheme from res/values/styles.xml on API 11+ devices. 
43.      
44.  API 11 theme customizations can go here.  
45.  
46.         Base application theme for API 14+. This theme completely replaces 
47.         AppBaseTheme from BOTH res/values/styles.xml and 
48.         res/values-v11/styles.xml on API 14+ devices. 
49.      
50.  API 14 theme customizations can go here.  
51.          */  
52.         public static final int AppBaseTheme=0x7f050000;  
53.         /**  Application theme.  
54.  All customizations that are NOT specific to a particular API-level can go here.  
55.          */  
56.         public static final int AppTheme=0x7f050001;  
57.     }  
58. }  

APK(Android Application package) File

An apk file is created by the framework automatically. If you want to run the android application on the mobile, transfer and install it.

Resources

It contains resource files including activity_main, strings, styles etc.

Manifest file

It contains information about package including components such as activities, services, content providers etc.




Dalvik Virtual Machine

As we know the modern JVM is high performance and provides excellent memory management. But it need to be optimized for low-powered handheld devices. The Dalvik Virtual Machine is optimized for mobile devices. It optimizes the JVM for memory, performance, and battery life.
Dalvik is the name of a town in Iceland. The Dalvik VM was written by Dan Bornstein.
The Dex compiler converts the class files into the .dex files that run on the Dalvik VM.
Let's see the compiling and packaging process from the source file:
The javac tool compiles the java source file into the class file.
The dx tool takes all the class files of your application and generates a single .dex file. It is a platform-specific tool.
The aapt (Android Assets Packaging Tool) handles the packaging process.



AndroidManifest.xml file in android

The AndroidManifest.xml file contains information about your package, including components of the application such as activities, services, content providers, broadcast receivers etc.
It performs some other tasks also:
  • It is responsible to protect the application to access any protected parts by providing the permissions.
  • It also declares the android api that the application is going to use.
  • It lists the instrumentation classes. The instumentation classes provides profiling and other informations. These informations are removed just before the application is published etc.
This is the required xml file for all the android application and located inside the root directory.
A simple AndroidManifest.xml file looks like this:
1.    <manifest xmlns:android="http://schemas.android.com/apk/res/android"  
2.        package="com.abc.hello"  
3.        android:versionCode="1"  
4.        android:versionName="1.0" >  
5.      
6.        <uses-sdk  
7.            android:minSdkVersion="8"  
8.            android:targetSdkVersion="15" />  
9.      
10.     <application  
11.         android:icon="@drawable/ic_launcher"  
12.         android:label="@string/app_name"  
13.         android:theme="@style/AppTheme" >  
14.         <activity  
15.             android:name=".MainActivity"  
16.             android:label="@string/title_activity_main" >  
17.             <intent-filter>  
18.                 <action android:name="android.intent.action.MAIN" />  
19.   
20.                 <category android:name="android.intent.category.LAUNCHER" />  
21.             </intent-filter>  
22.         </activity>  
23.     </application>  
24.   
25. </manifest>  

Elements of the AndroidManifest.xml file

The elements used in the above xml file are described below.

<manifest>

manifest is the root element of the AndroidManifest.xml file. It includes the namespace declaration. It haspackage attribute that describes the package name of the activity class.

<application>

application is the subelement of the manifest. It includes the namespace declaration. This element contains several subelements that declares the application component such as activity etc.
The commonly used attributes are of this element are icon, label, theme etc.
android:icon represents the icon for all the application components.
android:label works as the default label for all the application components. It should be set as a reference to string resource.
android:theme represents a common theme for all the activities.

<activity>

activity is the subelement of application and represents an activity. Each activity must be defined in the AndroidManifest.xml file. It has many attributes such as name, label etc.
android:label represents a label for the activity, often displayed on the screen.
android:name represents a name for the activity class. It is required attribute.

<intent-filter>

intent-filter is the subelement of activity and describes the type of intent to which activity, service or broadcast receiver can respond to.

<action>

It adds an action for the intent-filter. The intent-filter must have one or more action elements.

<category>

It adds an category name to an intent-filter.


R.java file in android
It is an auto-generated file by aapt (Android Asset Packaging Tool) that contains resouce IDs for all the resources of res/ directory.
If you create any component in the activity_main.xml file, id for the corresponding component is automatically created in this file. This id can be used in the activity source file to perform any action on the component.
1.    /* AUTO-GENERATED FILE.  DO NOT MODIFY. 
2.     * 
3.     * This class was automatically generated by the 
4.     * aapt tool from the resource data it found.  It 
5.     * should not be modified by hand. 
6.     */  
7.      
8.    package com.example.helloandroid;  
9.      
10. public final class R {  
11.     public static final class attr {  
12.     }  
13.     public static final class drawable {  
14.         public static final int ic_launcher=0x7f020000;  
15.     }  
16.     public static final class id {  
17.         public static final int menu_settings=0x7f070000;  
18.     }  
19.     public static final class layout {  
20.         public static final int activity_main=0x7f030000;  
21.     }  
22.     public static final class menu {  
23.         public static final int activity_main=0x7f060000;  
24.     }  
25.     public static final class string {  
26.         public static final int app_name=0x7f040000;  
27.         public static final int hello_world=0x7f040001;  
28.         public static final int menu_settings=0x7f040002;  
29.     }  
30.     public static final class style {  
31.         /**  
32.         Base application theme, dependent on API level. This theme is replaced 
33.         by AppBaseTheme from res/values-vXX/styles.xml on newer devices. 
34.      
35.  
36.             Theme customizations available in newer API levels can go in 
37.             res/values-vXX/styles.xml, while customizations related to 
38.             backward-compatibility can go here. 
39.          
40.  
41.         Base application theme for API 11+. This theme completely replaces 
42.         AppBaseTheme from res/values/styles.xml on API 11+ devices. 
43.      
44.  API 11 theme customizations can go here.  
45.  
46.         Base application theme for API 14+. This theme completely replaces 
47.         AppBaseTheme from BOTH res/values/styles.xml and 
48.         res/values-v11/styles.xml on API 14+ devices. 
49.      
50.  API 14 theme customizations can go here.  
51.          */  
52.         public static final int AppBaseTheme=0x7f050000;  
53.         /**  Application theme.  
54.  All customizations that are NOT specific to a particular API-level can go here.  
55.          */  
56.         public static final int AppTheme=0x7f050001;  
57.     }  
58. }  


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