Session 3 beccse

Dept. of Computer Science and Engineering

Application Building Blocks & Components

Android applications are composed of one or more application components

- Activity - Services - Intents - Content Providers - Broadcast Receivers


Activity

• An activity corresponds to a screen. If an application is composed of several screens, it has an activity for each screen.

• Each activity is a class that extends the base class called Activity. It has a graphical user interface made of views, and it responds to events. When you change screen, a new activity is launched and It can return a value

• The graphical interface of an activity is described by a Layout


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.


Application

• Create an application which calls one Activity into another


Intent

• Intents are verbs for android devices, which defines actions and are made effective by a new screen

E.g. CALL, SEND_MESSAGE.

• An intent is made up of an action and data that are URI.

• Components of an application — activities, services, and broadcast receivers , are activated through messages, called intents.

• In each case, the Android system finds the appropriate activity, service, or set of broadcast receivers to respond to the intent, instantiating them if necessary.


• Examples of actions: MAIN, VIEW, EDIT, PICK.

If one wants to see a card about a person, an intent is defined. The action is VIEW and the data is the URI which enables access to this card.

<intent-filter> <action android:name="android.intent.action.VIEW" /> <action android:name="android.intent.action.EDIT" /> <action android:name="android.intent.action.PICK" /> <category android:name="android.intent.category.DEFAULT" /> <data android:mimeType="vnd.android.cursor.dir/vnd.google.note" />

</intent-filter>


IntentFilters

• Describes how the action should apply.• To inform the system which implicit intents they can handle activities,

services, and broadcast receivers

IntentReceiver

• It is an object that responds to external events. It can operate in the application or it can start an application.

• Example of intent, view a webpage: VIEW for action and for data http://www.linkToStuff.org.

http://www.linktostuff.org./

http://www.linktostuff.org./


Content Provider

• Data stored by a program, in the form of files or SQLite databases are private and may not be used by other applications.

• That is to say, a SQLite database created on Android by one application is usable only by that application, not by other applications. Databases created in Android are visible only to the application that created them

• So, if you need to share data between applications, you need to use the content provider.


For example,

• The Android system provides a content provider that manages the user's contact information. As such, any application with the proper permissions can query part of the content provider to read and write information about a particular person.

• Content providers are also useful for reading and writing data that is private to your application and not shared. For example, the Note Pad sample application uses a content provider to save notes.


To query a content provider, you provide a query string in the form of a URI, with an optional specifier for a particular row, using the following syntax:

<standard_prefix>://<authority>/<data_path>/<id>

Similarly, to retrieve all the contacts stored by the Contacts application, the URI would look like this:

content://contacts/people


Broadcast receivers

• A broadcast receiver is a component that responds to system-wide broadcast announcements.

• Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured.

• Applications can also initiate broadcasts—for 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 don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs.


Services

• A service is a component that runs in the background to perform long-running operations . It’s a faceless component of a process.

• A service does not provide a user interface.

• A service is designed to operate independently of the screen, can update your data source and activities, and trigger specific notations.

• The best example is the music player that can work in background and when we can be in some other activity.


Layouts


Types of Layout

• Absolute Layout• Frame Layout• Linear Layout• Relative Layout• Table Layout


AbsoluteLayout• For each view you add,

you specify the exact screen coordinate to display on the screen


Frame Layout• designed to display a

single item at a time.• element will be

positioned based on the top left of the screen


Linear Layout• organizes elements along a single line.• Can specify whether that line is vertical or

horizontal using android:orientation.

android:orientation changed to horizontal.


Relative Layout• lays out elements

based on their relationships with one another, and with the parent container.


Table Layout• Organizes content into

rows and columns.


Tea Break

Come back at 4:00

Session 3 beccse

Education

computer science andthe

content provider data

application activities

email application

example of intent

new activity

android system

notepad sample application