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. This tutorial will teach you basic Android programming and will also take you through some advance concepts related to Android application development.
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.
Why Android?
Features of Android
Android is a powerful operating system competing with Apple 4GS and supports great features. Few of them are listed below −
Sr.No.
|
Feature & Description
|
1
|
Beautiful UI
Android OS basic screen provides a beautiful and intuitive user interface.
|
2
|
Connectivity
GSM/EDGE, IDEN, CDMA, EV-DO, UMTS, Bluetooth, Wi-Fi, LTE, NFC and WiMAX.
|
3
|
Storage
SQLite, a lightweight relational database, is used for data storage purposes.
|
4
|
Media support
H.263, H.264, MPEG-4 SP, AMR, AMR-WB, AAC, HE-AAC, AAC 5.1, MP3, MIDI, Ogg Vorbis, WAV, JPEG, PNG, GIF, and BMP.
|
5
|
Messaging
SMS and MMS
|
6
|
Web browser
Based on the open-source WebKit layout engine, coupled with Chrome's V8 JavaScript engine supporting HTML5 and CSS3.
|
7
|
Multi-touch
Android has native support for multi-touch which was initially made available in handsets such as the HTC Hero.
|
8
|
Multi-tasking
User can jump from one task to another and same time various application can run simultaneously.
|
9
|
Resizable widgets
Widgets are resizable, so users can expand them to show more content or shrink them to save space.
|
10
|
Multi-Language
Supports single direction and bi-directional text.
|
11
|
GCM
Google Cloud Messaging (GCM) is a service that lets developers send short message data to their users on Android devices, without needing a proprietary sync solution.
|
12
|
Wi-Fi Direct
A technology that lets apps discover and pair directly, over a high-bandwidth peer-to-peer connection.
|
13
|
Android Beam
A popular NFC-based technology that lets users instantly share, just by touching two NFC-enabled phones together.
|
Android Applications
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, SlideME, Opera Mobile Store, Mobango, F-droid and 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.
Categories of Android applications
What is API level?
API Level is an integer value that uniquely identifies the framework API revision offered by a version of the Android platform.
Platform Version
|
API Level
|
VERSION_CODE
|
|
Android 6.0
|
23
|
MARSHMALLOW
|
|
Android 5.1
|
22
|
LOLLIPOP_MR1
|
|
Android 5.0
|
21
|
LOLLIPOP
|
|
Android 4.4W
|
20
|
KITKAT_WATCH
|
KitKat for Wearables Only
|
Android 4.4
|
19
|
KITKAT
|
|
Android 4.3
|
18
|
JELLY_BEAN_MR2
|
|
Android 4.2, 4.2.2
|
17
|
JELLY_BEAN_MR1
|
|
Android 4.1, 4.1.1
|
16
|
JELLY_BEAN
|
|
Android 4.0.3, 4.0.4
|
15
|
ICE_CREAM_SANDWICH_MR1
|
|
Android 4.0, 4.0.1, 4.0.2
|
14
|
ICE_CREAM_SANDWICH
|
|
Android 3.2
|
13
|
HONEYCOMB_MR2
|
|
Android 3.1.x
|
12
|
HONEYCOMB_MR1
|
|
Android 3.0.x
|
11
|
HONEYCOMB
|
|
Android 2.3.4
Android 2.3.3
|
10
|
GINGERBREAD_MR1
|
|
Android 2.3.2
Android 2.3.1
Android 2.3
|
9
|
GINGERBREAD
|
|
Android 2.2.x
|
8
|
FROYO
|
|
Android 2.1.x
|
7
|
ECLAIR_MR1
|
|
Android 2.0.1
|
6
|
ECLAIR_0_1
|
|
Android 2.0
|
5
|
ECLAIR
|
|
Android 1.6
|
4
|
DONUT
|
|
Android 1.5
|
3
|
CUPCAKE
|
|
Android 1.1
|
2
|
BASE_1_1
|
|
Android 1.0
|
1
|
BASE
|
Android - Architecture
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 3.6 with approximately 115 patches. This provides a level of abstraction between the device hardware and it contains all the essential hardware drivers 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 Libraries
This category encompasses those Java-based libraries that are specific to Android development. Examples of libraries in this category include the application framework libraries in addition to those that facilitate user interface building, graphics drawing and database access. A summary of some key core Android libraries available to the Android developer is as follows −
android.app − Provides access to the application model and is the cornerstone of all Android applications.
android.content − Facilitates content access, publishing and messaging between applications and application components.
android.database − Used to access data published by content providers and includes SQLite database management classes.
android.opengl − A Java interface to the OpenGL ES 3D graphics rendering API.
android.os − Provides applications with access to standard operating system services including messages, system services and inter-process communication.
android.text − Used to render and manipulate text on a device display.
android.view − The fundamental building blocks of application user interfaces.
android.widget − A rich collection of pre-built user interface components such as buttons, labels, list views, layout managers, radio buttons etc.
android.webkit − A set of classes intended to allow web-browsing capabilities to be built into applications.
Having covered the Java-based core libraries in the Android runtime, it is now time to turn our attention to the C/C++ based libraries contained in this layer of the Android software stack.
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.
The Android framework includes the following key services −
Activity Manager − Controls all aspects of the application lifecycle and activity stack.
Content Providers − Allows applications to publish and share data with other applications.
Resource Manager − Provides access to non-code embedded resources such as strings, color settings and user interface layouts.
Notifications Manager − Allows applications to display alerts and notifications to the user.
View System − An extensible set of views used to create application user interfaces.
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.
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 −
Sr.No
|
Components & Description
|
1
|
Activities
They dictate the UI and handle the user interaction to the smart phone screen.
|
2
|
Services
They handle background processing associated with an application.
|
3
|
Broadcast Receivers
They handle communication between Android OS and applications.
|
4
|
Content Providers
They handle data and database management issues.
|
Activities
An activity represents a single screen with a user interface,in-short Activity performs actions on the screen. 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 broadcaster as an Intent object.
public class MyReceiver extends BroadcastReceiver {
public void onReceive(context,intent){}
}
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 {
public void onCreate(){}
A service is a component that runs in the background to perform long-running operations without needing to interact with the user and it works even if application is destroyed. A service can essentially take two states −
Sr.No.
|
State & Description
|
1
|
Started
A service is started when an application component, such as an activity, starts it by calling startService(). Once started, a service can run in the background indefinitely, even if the component that started it is destroyed.
|
2
|
Bound
A service is bound when an application component binds to it by calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, get results, and even do so across processes with interprocess communication (IPC).
|
Android - Broadcast Receivers
Broadcast Receivers simply respond to broadcast messages from other applications or from the system itself. These messages are sometime called events or intents. 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.
There are following two important steps to make BroadcastReceiver works for the system broadcasted intents −
Creating the Broadcast Receiver.
Registering Broadcast Receiver
There is one additional steps in case you are going to implement your custom intents then you will have to create and broadcast those intents.
A content provider component supplies data from one application to others on request. Such requests are handled by the methods of the ContentResolver class. A content provider can use different ways to store its data and the data can be stored in a database, in files, or even over a network.
Content URIs
To query a content provider, you specify the query string in the form of a URI which has the following format −
<prefix>://<authority>/<data_type>/<id>
A Fragment is a piece of an activity which enable more modular activity design. It will not be wrong if we say, a fragment is a kind of sub-activity.
Following are important points about fragment −
- A fragment has its own layout and its own behavior with its own life cycle callbacks.
- You can add or remove fragments in an activity while the activity is running.
- You can combine multiple fragments in a single activity to build a multi-plane UI.
- A fragment can be used in multiple activities.
An Android Intent is an abstract description of an operation to be performed. It can be used with startActivity to launch an Activity, broadcastIntent to send it to any interested BroadcastReceiver components, and startService(Intent) or bindService(Intent, ServiceConnection, int) to communicate with a background Service.
The intent itself, an Intent object, is a passive data structure holding an abstract description of an operation to be performed.
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