Android Application Development Fundamentals

Application Fundamentals Quickview mechanical man employments argon composed of 1 or to a greater extent employment comp superstarnts (activities, supporters, satisfy suppliers, and publicise liquidators) severally comp unitarynt performs a different role in the overall industriousness behavior, and each champion quarter be oxygenated individually ( tied(p) by other applications) The transparent filing cabinet must(prenominal) curb all instalments in the application and should likewise declare all application requirements, such(prenominal) as the minimum adaption of android required and all hardware configurations required Non-code application resources (images, strings, layout files, and so on should include alternatives for different art configurations (such as different strings for different languages and different layouts for different screen sizes) In this memorial 1. Application Components 1. touch off genes 2. The Manifest File 1. Declaring com ponents 2. Declaring application requirements 3. Application Resources humanoid applications are compose in the Java programming language. The Android SDK tools compile the codealong with any info and resource filesinto an Android package, an archive file with an . apk suffix. alone the code in a single . pk file is considered to be one application and is the file that Android-powered devices physical exertion to install the application. Once installed on a device, each Android application lives in its own security sandbox The Android operating clay is a multi- substance absubstance ab user Linux outline in which each application is a different user. By default, the arranging assigns each application a unique Linux user ID (the ID is used plainly by the system and is unknown to the application). The system sets permits for all the files in an application so that only the user ID assigned to that application tidy sum annoy them. Each wreak has its own virtual machine (VM), so an applications code releases in closing off from other applications. By default, every application runs in its own Linux swear out. Android fails the transit when any of the applications components pick up to be executed, then shuts down the process when its no longer needed or when the system must determine memory for other applications. In this way, the Android system implements the principle of to the lowest degree privilege. That is, each application, by default, has entree only to the components that it requires to do its work and no more.This creates a very secure environment in which an application house non access parts of the system for which it is not given permission. However, there are ship plentyal for an application to share data with other applications and for an application to access system armed services Its possible to arrange for two applications to share the same Linux user ID, in which case they are able to access each others files. To o bserve system resources, applications with the same user ID house besides arrange to run in the same Linux process and share the same VM (the applications must also be signed with the same certificate). An application can request permission to access device data such as the users contacts, SMS substances, the mountable memory board (SD card), tv camera, Bluetooth, and more. both application permissions must be granted by the user at install time. That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to The core framework components that define your application. The manifest file in which you declare components and required device features for your application. Resources that are separate from the application code and earmark your application to gracefully optimize its behavior for a variety of device configurations. Application Components Application components are the essential building blocks of an An droid application. Each component is a different point through which the system can enter your application. Not all components are actual entry points for the user and some depend on each other, but each one exists as its own entity and plays a particular proposition roleeach one is a unique building block that helps define your applications overall behavior. in that location are iv different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed. Here are the four types of application components Activities An activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, some other activity to compose an email, and some other activity for reading emails. Although the activities work together to form a viscid user experience in the email application, each one is case-by-case of the others.As suc h, a different application can start any one of these activities (if the email application allows it). For example, a camera application can start the activity in the email application that composes new mail, in order for the user to share a picture. An activity is implemented as a subclass of Activity and you can learn more nigh it in the Activities developer guide. Services A service is a component that runs in the ground to perform long-running operations or to perform work for remote processes.A service does not provide a user interface. 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. Another component, such as an activity, can start the service and let it run or bind to it in order to interact with it. A service is implemented as a subclass of Service and you can learn more about it in the Services developer guide. Content provide rs A study provider manages a shared set of application data.You can store the data in the file system, an SQLite database, on the web, or any other persistent storage location your application can access. Through the content provider, other applications can query or even modify the data (if the content provider allows it). For example, the Android system provides a content provider that manages the users contact information. As such, any application with the proper permissions can query part of the content provider (such as ContactsContract. Data) to read and write information about a particular person.Content providers are also useful for reading and paternity data that is private to your application and not shared. For example, the Note Pad try out application uses a content provider to save notes. A content provider is implemented as a subclass of ContentProvider and must implement a standard set of APIs that enable other applications to perform transactions. For more informa tion, see the Content Providers developer guide. Broadcast receivers A carry receiver is a component that responds to system-wide broadcast announcements.Many broadcasts originate from the systemfor example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured. Applications can also initiate broadcastsfor example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers dont display a user interface, they whitethorn create a status bar notification to alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a gateway to other components and is intended to do a very minimal amount of work.For instance, it might initiate a service to perform some work based on the event. A broadcast receiver is implemented as a subclass of BroadcastReceiver and each broadcast is delivered as an Intent object. For more informatio n, see the BroadcastReceiver class. A unique aspect of the Android system function is that any application can start another(prenominal) applications component. For example, if you want the user to capture a word-painting with the device camera, theres believably another application that does that and your application can use it, instead of maturation an activity to capture a photo yourself.You dont need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera application that captures a photo. When complete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is in truth a part of your application. When the system starts a component, it starts the process for that application (if its not already running) and instantiates the classes needed for the component. For xample, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera application, not in your applications process. Therefore, unlike applications on most other systems, Android applications dont have a single entry point (theres no main() function, for example). Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can.So, to activate a component in another application, you must deliver a message to the system that specifies your excogitation to start a particular component. The system then activates the component for you. energizing Components Three of the four component typesactivities, services, and broadcast receiversare activated by an asynchronous message called an intent. Intents bind individual components to each other at runtime (you can hypothesize of them as the messengers that request an action from other components), whether the component belongs to your application or another.An intent is created with an Intent object, which defines a message to activate either a specific component or a specific type of componentan intent can be either evident or implicit, respectively. A unique aspect of the Android system design is that any application can start another applications component. For example, if you want the user to capture a photo with the device camera, theres probably another application that does that and your application can use it, instead of developing an activity to capture a photo yourself. You dont need to incorporate or even link to the code from the camera application.Instead, you can simply start the activity in the camera application that captures a photo. When complete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application. When the system starts a component, it star ts the process for that application (if its not already running) and instantiates the classes needed for the component. For example, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera pplication, not in your applications process. Therefore, unlike applications on most other systems, Android applications dont have a single entry point (theres no main() function, for example). Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can. So, to activate a component in another application, you must deliver a message to the system that specifies your intent to start a particular component.The system then activates the component for you. Activating Components Three of the four component typesactivities, services, and broadcast receiversare activated by an asynchronous message called an intent. Intents bind individual components to each other at runtime (you can think of them as the messengers that request an action from other components), whether the component belongs to your application or another. An intent is created with an Intent object, which defines a message to activate either a specific component or a specific type of componentan intent can be either explicit or implicit, respectively.