Category: Android

Android – Architecture ”; Previous Next 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. Print Page Previous Next Advertisements ”;

Android – Hello World Example ”; Previous Next Let us start actual programming with Android Framework. Before you start writing your first example using Android SDK, you have to make sure that you have set-up your Android development environment properly as explained in Android – Environment Set-up tutorial. I also assume that you have a little bit working knowledge with Android studio. So let us proceed to write a simple Android Application which will print “Hello World!”. Create Android Application The first step is to create a simple Android Application using Android studio. When you click on Android studio icon, it will show screen as shown below You can start your application development by calling start a new android studio project. in a new installation frame should ask Application name, package information and location of the project.− After entered application name, it going to be called select the form factors your application runs on, here need to specify Minimum SDK, in our tutorial, I have declared as API23: Android 6.0(Mashmallow) − The next level of installation should contain selecting the activity to mobile, it specifies the default layout for Applications. At the final stage it going to be open development tool to write the application code. Anatomy of Android Application Before you run your app, you should be aware of a few directories and files in the Android project − Sr.No. Folder, File & Description 1 Java 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 res/drawable-hdpi This is a directory for drawable objects that are designed for high-density screens. 3 res/layout This is a directory for files that define your app”s user interface. 4 res/values This is a directory for other various XML files that contain a collection of resources, such as strings and colours definitions. 5 AndroidManifest.xml This is the manifest file which describes the fundamental characteristics of the app and defines each of its components. 6 Build.gradle This is an auto generated file which contains compileSdkVersion, buildToolsVersion, applicationId, minSdkVersion, targetSdkVersion, versionCode and versionName Following section will give a brief overview of the important application files. 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.support.v7.app.AppCompatActivity; import android.os.Bundle; public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } } Here, R.layout.activity_main refers to the activity_main.xml file located in the res/layout folder. The onCreate() method is one of many methods that are figured when an activity is loaded. The Manifest File Whatever component you develop as a part of your application, you must declare all its components in a manifest.xml which resides 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 − <?xml version=”1.0″ encoding=”utf-8″?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”com.example.tutorialspoint7.myapplication”> <application android:allowBackup=”true” android:icon=”@mipmap/ic_launcher” android:label=”@string/app_name” android:supportsRtl=”true” android:theme=”@style/AppTheme”> <activity android:name=”.MainActivity”> <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. Attribute android: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 specifies 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 app_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 − <activity>elements for activities <service> elements for services <receiver> elements for broadcast receivers <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 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 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” > <TextView android: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 have 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! application we just created. I assume you had created

Android – Services ”; Previous Next 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). A service has life cycle callback methods that you can implement to monitor changes in the service”s state and you can perform work at the appropriate stage. The following diagram on the left shows the life cycle when the service is created with startService() and the diagram on the right shows the life cycle when the service is created with bindService(): (image courtesy : android.com ) To create an service, you create a Java class that extends the Service base class or one of its existing subclasses. The Service base class defines various callback methods and the most important are given below. You don”t need to implement all the callbacks methods. However, it”s important that you understand each one and implement those that ensure your app behaves the way users expect. Sr.No. Callback & Description 1 onStartCommand() The system calls this method when another component, such as an activity, requests that the service be started, by calling startService(). If you implement this method, it is your responsibility to stop the service when its work is done, by calling stopSelf() or stopService() methods. 2 onBind() The system calls this method when another component wants to bind with the service by calling bindService(). If you implement this method, you must provide an interface that clients use to communicate with the service, by returning an IBinder object. You must always implement this method, but if you don”t want to allow binding, then you should return null. 3 onUnbind() The system calls this method when all clients have disconnected from a particular interface published by the service. 4 onRebind() The system calls this method when new clients have connected to the service, after it had previously been notified that all had disconnected in its onUnbind(Intent). 5 onCreate() The system calls this method when the service is first created using onStartCommand() or onBind(). This call is required to perform one-time set-up. 6 onDestroy() The system calls this method when the service is no longer used and is being destroyed. Your service should implement this to clean up any resources such as threads, registered listeners, receivers, etc. The following skeleton service demonstrates each of the life cycle methods − package com.tutorialspoint; import android.app.Service; import android.os.IBinder; import android.content.Intent; import android.os.Bundle; public class HelloService extends Service { /** indicates how to behave if the service is killed */ int mStartMode; /** interface for clients that bind */ IBinder mBinder; /** indicates whether onRebind should be used */ boolean mAllowRebind; /** Called when the service is being created. */ @Override public void onCreate() { } /** The service is starting, due to a call to startService() */ @Override public int onStartCommand(Intent intent, int flags, int startId) { return mStartMode; } /** A client is binding to the service with bindService() */ @Override public IBinder onBind(Intent intent) { return mBinder; } /** Called when all clients have unbound with unbindService() */ @Override public boolean onUnbind(Intent intent) { return mAllowRebind; } /** Called when a client is binding to the service with bindService()*/ @Override public void onRebind(Intent intent) { } /** Called when The service is no longer used and is being destroyed */ @Override public void onDestroy() { } } Example This example will take you through simple steps to show how to create your own Android Service. Follow the following steps to modify the Android application we created in Hello World Example chapter − Step Description 1 You will use Android StudioIDE to create an Android application and name it as My Application under a package com.example.tutorialspoint7.myapplication as explained in the Hello World Example chapter. 2 Modify main activity file MainActivity.java to add startService() and stopService() methods. 3 Create a new java file MyService.java under the package com.example.My Application. This file will have implementation of Android service related methods. 4 Define your service in AndroidManifest.xml file using <service…/> tag. An application can have one or more services without any restrictions. 5 Modify the default content of res/layout/activity_main.xml file to include two buttons in linear layout. 6 No need to change any constants in res/values/strings.xml file. Android studio take care of string values 7 Run the application to launch Android emulator and verify the result of the changes done in the application. Following is the content of the modified main activity file MainActivity.java. This file can include each of the fundamental life cycle methods. We have added startService() and stopService() methods to start and stop the service. package com.example.tutorialspoint7.myapplication; import android.content.Intent; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.os.Bundle; import android.app.Activity; import android.util.Log; import android.view.View; public class MainActivity extends Activity { String msg = “Android : “; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Log.d(msg, “The onCreate() event”); } public void startService(View view) { startService(new Intent(getBaseContext(), MyService.class)); } // Method to stop the service public void stopService(View view) { stopService(new Intent(getBaseContext(), MyService.class)); } } Following is the content of MyService.java. This file can have implementation of one or more methods associated with Service based on requirements. For now we are going to implement only two methods onStartCommand() and onDestroy() − package com.example.tutorialspoint7.myapplication; import android.app.Service; import android.content.Intent; import android.os.IBinder; import android.support.annotation.Nullable; import android.widget.Toast; /** * Created by TutorialsPoint7 on

Android – Overview ”; Previous Next What is Android? 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. Android offers a unified approach to application development for mobile devices which means developers need only develop for Android, and their applications should be able to run on different devices powered by Android. 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. On June 27, 2012, at the Google I/O conference, Google announced the next Android version, 4.1 Jelly Bean. Jelly Bean is an incremental update, with the primary aim of improving the user interface, both in terms of functionality and performance. The source code for Android is available under free and open source software licenses. Google publishes most of the code under the Apache License version 2.0 and the rest, Linux kernel changes, under the GNU General Public License version 2. 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 There are many android applications in the market. The top categories are − History of Android The code names of android ranges from A to N currently, such as Aestro, Blender, Cupcake, Donut, Eclair, Froyo, Gingerbread, Honeycomb, Ice Cream Sandwitch, Jelly Bean, KitKat, Lollipop and Marshmallow. Let”s understand the android history in a sequence. 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 Print Page Previous Next Advertisements ”;

Android – Application Components ”; Previous Next 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(){} } We will go through these tags in detail while covering application components in individual chapters. Additional Components There are additional components which will be used in the construction of above mentioned entities, their logic, and wiring between them. These components are − S.No Components & Description 1 Fragments Represents a portion of user interface in an Activity. 2 Views UI elements that are drawn on-screen including buttons, lists forms etc. 3 Layouts View hierarchies that control screen format and appearance of the views. 4 Intents Messages wiring components together. 5 Resources External elements, such as strings, constants and drawable pictures. 6 Manifest Configuration file for the application. Print Page Previous Next Advertisements ”;