Android Application Development Training in Chandigarh

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Android Operation System

• Android is an operating system based on Linux with a Java programming interface.
• The Android Software Development Kit (Android SDK) provides all necessary tools to develop Android applications. This includes a compiler, debugger and a device emulator, as well as its own virtual machine to run Android programs.
• Android is currently primarily developed by Google.
• Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.

                                                                 

• Android applications consist of different components and can re-use components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task.
• For example you can write an application which uses the Android Gallery application to pick a photo.
• For example you can write an application which uses the Android Gallery application to pick a photo.
• Google offers the Google Play service in which programmers can offer their Android application to Android users. Google phones include the Google Play application which allows to install applications.
• Google Play also offers an update service, e.g. if a programmer uploads a new version of his application to Google Play, this service will notify existing users that an update is available and allow to install it.
• Google Play used to be called Android Market.
• Security and permissions
• During deployment on an Android device, the Android system will create a unique user and group ID for every Android application. Each application file is private to this generated user, e.g. other applications cannot access these files.
• In addition each Android application will be started in its own process.
• In addition each Android application will be started in its own process.
• If data should be shared, the application must do this explicitly, e.g. via a Service or a Content Provider.
• Android also contains a permission system. Android predefines permissions for certain tasks but every application can define additional permissions.
• An Android application declares its required permissions in its AndroidManifest.xml configuration file. For example an application may declare that it requires Internet
• Permissions have different levels. Some permission are automatically granted by the Android system, some are automatically rejected
• In most cases the requested permissions will be presented to the user before installation of the application. The user needs to decide if these permissions are given to the application.
• If the user denies permission required by the application, this application cannot be installed. The check of the permission is only performed during installation; permissions cannot be denied or granted after the installation.
• Not all users pay attention to the required permissions during installation. But some users do and they write negative reviews on Google Play.
• Android components
• The following gives a short overview of the most important Android components.
• An Activity represents the presentation layer of an Android application. A simplified description is that an Activity represents a screen in your Android application. This is slightly incorrect as Activities can be displayed as dialogs or can be transparent.
• An Android application can have several Activities.
• Views are user interface widgets, e.g. buttons or text fields. The base class for all Views is the android. View class. Views have attributes which can be used to configure their appearance and behavior.
• View Groups can be nestled to create complex layouts. You should not nestle View Groups too deeply as this has a negative impact on the performance.
• Intents are asynchronous messages which allow the application to request functionality from other components of the Android system, e.g. from Services or Activities. An application can call a component directly (explicit Intent) or ask the Android system to evaluate registered components based on the Intent data (implicit Intents). For example the application could implement sharing of data via Intent and all components which allow sharing of data would be available for the user to select. Applications register themselves to Intent via an Intent Filter.
• Intents allow combining loosely coupled components to perform certain tasks.
• Services perform background tasks without providing a user interface. They can notify the user via the notification framework in Android.
• A Content Provider provides a structured interface to application data. Via a Content Provider your application can share data with other applications. Android contains an SQLite database which is frequently used in conjunction with a Content Provider. The SQLite database would store the data, which would be accessed via the Content Provider.
• Broadcast Receiver can be registered to receive system messages and Intents. A Broadcast Receiver will get notified by the Android system, if the specified situation happens. For example a Broadcast Receiver could get called once the Android system completed the boot process or if a phone call is received.
• Widgets are interactive components which are primarily used on the Android home screen. They typically display some kind of data and allow the user to perform actions via them. For example a Widget could display a short summary of new emails and if the user selects an email, it could start the email application with the selected email.
• Android provide many more components but the list above describes the most important ones. Other Android components are Live Folders and Live Wallpapers. Live Folders display data on the home screen without launching the corresponding application while Live Wallpapers allow creating animated backgrounds.
• Android Development Tools
• The Android Software Development Kit (SDK) contains the necessary tools to create, compile and package Android application. Most of these tools are command line based.
• The Android SDK also provides an Android device emulator, so that Android applications can be tested without a real Android phone. You can create Android virtual devices (AVD) via the Android SDK, which run in this emulator.
• The Android SDK contains the Android debug bridge (ADB) tool which allows connecting to an virtual or real Android device.
• Google provides the Android Development Tools (ADT) to develop Android applications with Eclipse. ADT is a set of components (plug-ins) which extend the Eclipse IDE with Android development capabilities.
• ADT contains all required functionalities to create, compile, debug and deploy Android applications from the Eclipse IDE. ADT also allows creating and starting AVDs.
• The Android system uses a special virtual machine, i.e. the Dalvik Virtual Machine to run Java based applications. Dalvik uses an own byte code format which is different from Java byte code.
• Therefore you cannot directly run Java class files on Android, they need to get converted in the Dalvik byte code format.
• Android applications are primarily written in the 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 class files into a file. All class files of one application are placed in one compressed .dex file. During this conversion process redundant information in the class files are optimized in the .dex file. For example if the same String is found in different class files, the .dex file contains only once reference of this String.
• These dex files are therefore much smaller in size than the corresponding class files.
• The .dex file and the resources of an Android project, e.g. the images and XML files, are packed into an .apk (Android Package) file. The program aapt (Android Asset Packaging Tool) performs this packaging.
• The .dex file and the resources of an Android project, e.g. the images and XML files, are packed into an .apk (Android Package) file. The program aapt (Android Asset Packaging Tool) performs this packaging.
• The Android Development Tools (ADT) performs these steps transparently to the user.
• If you use the ADT tooling you press a button the whole Android application (.apk file) will be created and deployed.
• The ADT allows the developer to define certain artifacts, e.g. Strings and layout files, in two ways: via a rich editor, and directly via XML. This is done via multi-page editors in Eclipse. In these editors you can switch between both representations by clicking on the tab on the lower part of the screen.