Android is a Linux-based operating system designed primarily for touchscreen mobile devices such as smartphones and tablet computers. It is currently developed by Google in conjunction with the Open Handset Alliance
Android is a Linux-based operating systemdesigned primarily for touchscreen mobile devices such as smartphones and tablet computers.
It is currently developed by Google in conjunction with the Open Handset Alliance.[2]
Initially developed by Android Inc, whom Google financially backed and later purchased in 2005,
Open Source:
Google releases the Android code as open source, under the Apache License.
The Android Open Source Project (AOSP), led by Google, is responsible with the maintenance and further development of Android.
Android Apps:
Additionally, Android has a large community of developers writing applications ("apps") that extend the functionality of devices, written primarily in a customized version of Java.
Creating Android Application:
Download the Android SDK.
Install the ADT plugin for Eclipse (if you’ll use the Eclipse IDE).
Download the latest SDK tools and platforms using the SDK Manager.
What is Android?
Android is an operating system which is based on Linux with Java Programming Interface.
Android SDK:
The Android Software Development kit provides the following necessary tools for the developing the Android Applications.
Android Application can re-use components of other applications using its different components.
Android Components:
Activity
It represents the presentation layer of an Android application. It presents a screen in your application. Activity can be displayed as dialogues or can be Transparent. An Android application can have several activities.
Views and View Groups:
“Views” are user interface widgets. The base class for all the views is android .View.views has attributes which is used to configure their appearance and behaviour.
A “View Groups” is for arranging other views. They are also called as layout managers the base class for “view Groups” I android.View.viewgroup which extends the class.
In order create complex layout View Groups can be nestled. It should not too deeply nestled since has a negative impact on the performance.
Intents:
These are asynchronous message which allows application in order to request functionality from other components of the Android Systems.
Applications register themselves to intent via an Intents filter. To perform certain tasks Intents allow to combine loosely coupled Components.
Services:
Services perform background tasks without providing a user Interface can notify the user via the notification framework in Android.
Content Provider:
It provider a structured interface to application data via a content provider applications can share data from one to another. Along with content provider SQ Lite database is used in conjunction. The SQ Lite database stores the data which is accessed by content provider.
Broadcast Receiver
Broadcast receiver registers the messages and Intents In the case when specified situation happens a Broadcast receiver will get notified by the Android system.
Widgets (Home Screen)
These are interactive components used on the Android home screen. They display a kind of data and allow user to perform via them.
Android Development Tools
Android SDK
The Android software Development kit (SDK) contains tools to:
Create application
Compile application
Package application
Most of these are command line based the android SDK also provides.
Android device emulator can be tested without a real Android phone.
You can create Android Virtual devices via the Android SDK which runs emulator.
ADB:
The Android SDK Contains the Android debug bridge (ADB) tool which along to connect to a virtual or real Android Device.
Android development Tools (ADT)
Google provides ADT to develop Android applications with Eclipse. It is a set of components which extends the Eclipse with Android development capabilities.
A deploy Android applications from the eclipse IDE, ADT allows to create and start AVDs.
Dalvik Virtual Machine
The special virtual machine used Android system is Dalvik to run Java based applications. It uses its own byte code format which different from java byte code.
Java files cannot run on Android directly. They Should be converted in the Dalvik byte code format.
How to develop Android Application?
Android Applications are primarily written in Java programming language. The Java source files are converted to java class files by the java compiler.
The Android SDK Contains a tool called “dx” which converts Java files to “.dex” (Dalvik Executable) file. All files are compressed in one .dex redundant information in class file are optimized in .dex file.
dex file are smaller in size than class files. The dex file resources of an Android project are packed in “.apk” (Android Package) file. “aapt” (Android Asset Packaging Tool) performs this packaging.
Via the adb tool the necessary data in .apk file is run and deployed to an Android device.
The ADT (Android Development Tools) performs these steps transparently to the user. If you use the ADT tooling you press a button and a whole Android Application is created and deployed.
Android Application Architecture
AndroidManifest.xml file:
The Components and settings of an Android application are described in the AndroidManifest.xml file. It should also contain the permissions for the application.
The Package attribute defines the base package for the java objects referred to in file. If a Java object lies within a different package. It must be declared with the full qualified package name Google Play requires that every Android Application has it own unique package. Hence, it is good to use reverser domain name as package name. It will avoid confusions and Collisions with other applications. android:versionName and android:versionCode specify the version of your application version name is what the user sees and can be an integer. The Android Market determination is based on the version code. You start with “1” if you need it do perform an update of existing installations and increase the “1” value by one if you roll-out a new version of your application.
The tag defines an Activity in this example pointing to convert class in the com.example package. Intent filter is registered for this.
R.Java and Resource
The gen directory is an Android project contains the generated values R.java is a generated class that contains references to certain resources of the project resources must be defined in the “res” directory and can be XML files icons or pictures.
If you are creating new resources the reference is automatically created in R.Jave via the Eclipse ADT tools. These are static integer values and define IDs for the resources. In order to access the corresponding resource via these IDs the Android System provides methods.
R.Java is automatically created by the Eclipse development environment manual changes are not necessary and will be overridden by the tooling.
Assets
The “assets” directory can be used to store any kind of data while the “res” directory contains structured values which are known to the Android platform. You can access this data via the “Assets Manager” through which you can access the “get Assets” method.
Via “Layouts” the user interface for “Activities” is defined. The layout defines the included “Views” (Widgets) and it properties.
A Layout can be defined either through java code or through XML. Most of the since it is defined in XML file only. The Layouts are defined via resource file in the /res/layout folder. This specifies he “View Groups”, Views, for this layout.
To access a View through Java Code, you have to give it a unique ID via the “android:id” attribute. To assign a new ID to a “view” use @+id/yourvalue .
Layouts are defined is XML because this separates the Logic from the layout definition. If also allows the definitions of different layouts. You can mix both approaches.
Reference to resource is XML files
In XML files you can refer to other resource via the @ sign.
Activities and Life cycle
The Android system Controls the life cycle of your Application. The Android system may stop or destroy your application. Through predefined methods the Android system defines a life cycle “Activities” Important are:
onSaveInstanceState() – Called after the Activity is stopped it is used to save data so that the “Activity ” Can restore its states if re-started
onPause()- always called if the Activity ends. Can be used to release resource or save data
onResume() – called if the “Activity” is restarted can be used to initialize fields.
Configuration Change
When Configuration on change happens an Activity will be restarted. It An event which is relevant for the application is triggered configuration change occurs* for eg: if the user Changes the orientation of the device (either vertically or horizontally) Android assumes that an ‘Activity’ may wanted to use different resources for those orientations and restarts the Activity.
In the emulator you can stimulate the change of the orientation via Ctrl+F11
Restart of application can be avoided by following in case of orientation change or position of the physical keyboard.
The following assumes that you have already java and eclipse installed and know how to use eclipse.
Pre-requisites for using a 64bit Linux
The Android SDK is 32bit, hence, on a 64 bit Linux system you need to have the package ia32-libs installed. For Ubuntu you can do this via the following command.
Use the Eclipse update manager to install all available components for the Android Development Tools (ADT). After the new Android development components are installed you would be prompted to install the android SDK.
Manual Installation of the Android SDK:
After the installation of the ADT automatically the Eclipse tooling allows todownload the Android.
The download contains a zip file, which you can extract to any place is your file system you may experience problems with the usage of the Android SDK. So avoid using spaces is the path name.
You should also define the location of the android SDK in the Eclipse Preference in eclipse open the preferences dialog via the Menu windows –> Preferences to select Android and enter the installation path of the Android SDK.
Install a specific Android version
The Android SDK Manager allows you to install specific versions of Android.
Select Windows –> Android SDK Manager from the Eclipse menu
The dialog allow you to install new packages and also you to delete them. Select “Available Packages” and open the third party Add-Ons Select the Google AP115 (Android 4.03) Version of the SDK and press the install button.
Android Virtual device Emulator
What is Android Emulator?
To run an Android system the Android Development Tools (ADT) include an emulator It Allows you to test your application without having a real device. The emulator behaves like a real device.
They can be defined with different Configuration. These devices are called as Android Virtual Device and you can start several in parallel.
Google vs Android AVD
You decide whether you want an Android device or a Google device during the creation of an AVD. An AVD which is created for Android will contain the programs from the Android open source project. An AVD, Which is created for the Google API’s, will contain several application and the notable one is Google Map Application.
Emulator Shortcuts
To work with emulator the following are the shortcuts.
“Alt+Enter” maximizes the emulator.
“Ctrl+F11” change the orientation of the emulator
“F8” Turns networks on/off ]
Performance
The native GPU of the Computer can be used by the graphics of the emulator. This will make the rendering in the emulator very fast to enable this add the GPU Emulation property to the device configuration and set it to true.
You can also get the “Enabled” flag for the snapshot. This will save the state of the emulator and will let it start much faster. And native GPU rendering and snapshots do not work together currently.
Hardware button
Android 4.0 introduces devices that do not have hardware any more if you want to create such AVD add the Hardware “Back/Home keys” Property to the device configuration and set it to ‘false’.
Create and run Android Virtual Device
To define an Android virtual Device Define (AVD) open the AVD Manager dialog via windows –> AVD manager and press ”new button”.
Enter the values similar to the Screenshot.
Select the Enabled for snapshot box. This will make the second start of the virtual device much faster. Press the create AVD button This will create the AVD Configuration and display it under the virtual devices.
Select your devices and press”start” button to test your setup is correct.
The AVD start after sometime Interputting this process might correct the AVD. You can use the AVD via the mouse and he virtual keyboard of the emulator after the AVD started.
How to make an android Application?
Install the demo application
This application is also available on the Android Market place. To install if via the google play application you can also scan following barcode with your android Smartphone alternatively.
Create Projects
Select file –> New–> other–> Android Project and create the Android Project enter the following.
Press ‘Finish’ this should create the following directory structure.
ADT provide specialized editor for resource files as described in the android Development Tools. These allows to between XML representation of file and rich user interface through tabs on the button of the editor.
Create attributes
Android allows you to create static attributes. These attributes can for example be used in your XML layout files or referred to via Java source code.
Select the file “res/values/string /CXML” and press the ‘Add’ button select ‘color’ and enter my color as the name and “3399CC” as the value.
Add the following “string” attributes string attributes allow the developer to translate the application at a later point.
Switch to the XML representation and validate that the values are correct.
Hello World, Convert!
Temperature Converter
#3399CC myClickHandler
to Celsius
to Fahrenheit
Calculate
Add Views
Select “res/layout/main.XML/” and open the Android editor via a double click. This editor allows you to create the layout via drag and drop or via the xml source code. You can switch between both representation via the tabs at the bottom of the editor for changing the position and grouping elements you can use the eclipse “Outline” View.
The following screenshot of the “palette” view from which you can drag and drop new user interface components into your layout. Note that the”Palette” view changes frequently so your view might be a bit different.
You will now create your new layout to remove the text object right click on the existing text object “Hello World Hello” in the layout select “delete” from the popup menu. Then from the “Palette” view select Text fields and locate “Text fields” derive from the class “Edit text” they just specify via an additional attributes which text type can be used.
Then select the Palette section “Form widgets” and drag a “Radio Group” Object onto the layout. The number of radio button added to the radio button group depends on your version of Eclipse. Make sure there are two radio buttons by deleting or adding radio buttons to the group.
From the palette section from widgets drag a button object onto the layout. The result should look as follows.
Switch to ’main.xml’and verify that your xml looks like the following.
android:layout_width=”fill_parent”
android:layout_height=”fill_parent”
android:orientation=”vertical” >
android:id=”@+id/editText1″
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:text=”EditText” >
android:id=”@+id/radioGroup1″
android:layout_width=”match_parent”
android:layout_height=”wrap_content” >
android:id=”@+id/radio0″
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:checked=”true”
android:text=”RadioButton” >
android:id=”@+id/radio1″
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:text=”RadioButton” >
android:id=”@+id/button1″
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:text=”Button” >
Edit View properties
You change user interface components properties via the eclipse ‘properties’ view if you select it most of the properties can be changed via the right mouse menu you can also edit properties of field directly in xml If you know what you want you to change, changing properties in the XML file is much faster. If you are searching for a certain properties the right mouse functionality is rice.
Open your main.xml layout file the edit text control shows currently a default text you need to delete it in the xml code. Switch to the xml tab called ‘main.xml’ and delete the android:text=”EditText” property from the edit text part switch back to the Graphical layout tab and check that the text is removed.
Use the right mouse click on the first radio button to assign the “Celsius” string attribute to its “text” property Assign the “fahrenheit” string to the second radio button.
You can always either edit the xml file or modify the properties via right mouse click.
Set the property”Checked” to true for the first Radio Button. Assign “Calc” to text property of your button and assign “myClickHandler” to the ‘on click’ property.
Set the “Input type” Property to “number signed” and “numberDecimal” on your edit text.
In a Linear layout all your user Interface Components are contained you need to assign a background color to this “LinearLayout” Right click on an empty space in graphical layout mode then select other properties–>All by name –> Background select ‘color’ and then select ‘mycolor’ in the list which is displayed.
Switch to the main.xml tab and verify that the xml is correct.
android:layout_width=”fill_parent”
android:layout_height=”fill_parent”
android:background=”@color/myColor”
android:orientation=”vertical” >
android:id=”@+id/editText1″
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:inputType=”numberDecimal|numberSigned” >
android:id=”@+id/radioGroup1″
android:layout_width=”match_parent”
android:layout_height=”wrap_content” >
android:id=”@+id/radio0″
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:checked=”true”
android:text=”@string/celsius” >
android:id=”@+id/radio1″
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:text=”@string/fahrenheit” >
android:id=”@+id/button1″
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:onClick=”myClickHandler”
android:text=”@string/calc” >
Change the Activity source Code
You specified that an “activity” called “convert activity” should be created during the, generation of view Android project. The project wizard created based on the ‘onclick’ property of your button.
package de.vogella.android.temperature;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.Toast;
publicclass ConvertActivity extends Activity {
private EditText text;
@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
text = (EditText) findViewById(R.id.editText1);
}
// This method is called at button click because we assigned the name to the
