10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Introduction to Android
•Overview of Android System
•Android Components
•Component lifecycles
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Android Introduction
FAndroid OS is based the Linux Kernel
FAimed at small-scale devices
–Phones, tablets, TVs, games consoles…
–Touch screen or mouse/pointer
–Small internal memory (256Mbyte to 3GB)
–Usually low power devices
FAccess to multiple sensors
–Accelerometers (up down etc)
–Proximity, Light, Magnetic
–Geo location (GPS etc)
FResources defined in XML documents rather than inside code
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Android OS Features
FApplication framework enabling reuse and replacement ofcomponents
FDalvik virtual machine optimized for mobile devices
FOptimized graphics powered by a custom 2D graphics library; 3Dgraphics based on (at least) OpenGL ES 1.0 specification, hardwareacceleration optional but common
FSQLite for structured data storage
FMedia support for common audio, video, and still image formats
FTelephony, Bluetooth and WiFi (hardware dependent)
FCamera, GPS, compass, and accelerometer (hardware dependent)
FRich development environment including a device emulator, toolsfor debugging, memory and performance profiling, and a plugin forthe Eclipse IDE
Android OS Structure
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Android Application Components
FComponents
–Activities – most important for us
–Services, “Broadcast Receivers”, “Content Providers”
F“Intents” are used to activate components
–Can use existing apps within your app, very easy todo
FIntent Filters define what a component can do
FThe Manifest file is where most app capabilitiesare declared
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Activity
–Eg a Text messaging app might have activities to
•show list of contacts
•write message
•review old messages
•change settings
–They work together but each is independent
FOne of the activities in identified as the first to belaunched.
FMoving from one activity to another is accomplished bythe current activity starting the next one.
FEach activity has a default window to draw in.
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Views
FEach view controls a rectangular space within thewindow.
FParent view contain children views.
FReady made views to use include:-
–Buttons
–Text Fields
–Scroll bars
–Menu items
–Check boxes etc
FBuild in the GUI designer!
A contains
B Contains
C Contains
D detail
E detail
Fdetail
G detail
H detail
K detail
I detail
J detail
L
M
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Services
FA service does not have a visual user interface
FRuns in the background for an indefinite period
–Eg service might play background music as user does somethingelse.
–Might fetch data over the network
–Calculate something
–Provide a result to an activity
FServices run in the main thread of the applicationprocess.
–Don’t block other components or user interface
–Often spawn another thread for time consuming tasks
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Broadcast Receivers
FA component that does nothing but receive and react tobroadcast announcements.
FMany broadcasts originate in system code
–Eg timezone change announcement
–Battery low announcement
–Picture has been taken announcement
FApplications can initiate broadcasts
–Data has been downloaded and ready to use
FAn application can have any number of broadcastreceivers
FNotifications are often used by them.
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Content Providers
FThe data can be stored
–in the file system
–Some other manner that makes sense.
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Intents
– activities, services and broadcast receivers.
FFor activities and services it
–Names the action being requested
–Specifies the URI of the data to act on
•Allow user to edit some specific text
FEach type of component is activated by sending an intent object to
•Android delivers the intent to all interested broadcast receivers by calling theirOnreceive() method.
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
The Manifest File
FApplications declare their components in amanifest file bundled in the Android package.apk
FThe manifest is an XML file.
FIt also
–Names any libraries needed to run app
–Identify any permissions the app needs
–Declares intent filters (what can the app do)
Example Manifest document
F<?xml version="1.0" encoding="utf-8"?><manifest . . . > <application . . . > <activity android:name="com.example.project.FreneticActivity" android:icon="@drawable/small_pic.png" android:label="@string/freneticLabel" . . . > <intent-filter . . . > <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> <intent-filter . . . > <action android:name="com.example.project.BOUNCE" /> <data android:mimeType="image/jpeg" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </activity> . . . </application></manifest>
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Activity Lifecycle
FAn activity has three states
–Active or running when in the foreground ie has the focus for the user’sactions
–Paused if it has lost focus but is still visible
•A paused activity is completely alive
•Can be killed by the system in extreme low memory situations
–Stopped if completely obscured by another activity.
•It still retains all state and member information
•Often killed by the system when memory needed elsewhere
FAs activity state changes various methods called:-
–onCreate(), onStart(),
–onRestart(), onResume(),
–onPause(), onStop(),
–onDestroy()
Activity Starts
Process is killed
Activity is running
Activity is no longer visible
Activity is shut down
OnCreate()
OnResume()
OnDestroy()
OnStop()
OnStart()
OnPause()
Another Activity in front
Activity comesto theForeground
Activitycomes to theForeground
User navigatesback to theactivity
Other Applicationsneed memory
OnRestart()
Activity Lifecycle
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Service and Broadcast ReceiverLifecycle
FA service
–can be started or stopped
•Methods available
–onCreate()
–onStart()
–onDestroy()
•If the service permits others to bind it additional methods are
–onBind()
–onUnbind()
–onRebind()
FA Broadcast receiver has on one callback method
–onReceive()
Service is started bystartService()
Service is running
Service is shut down
OnCreate()
OnDestroy()
OnStart()
The dervice is stopped
(no callback)
Service Lifecycle
Service is started bybindService()
Service is shut down
OnCreate()
OnDestroy()
OnBind()
Client interacts with the service
OnUnbind()
OnRebind()
10/10/2015
E.R.Edwards 10/10/2015
Staffordshire University
School of Computing
Summary
FAndroid is open source – anyone can join in!
FFairly radical change in perspective makingprogramming interesting!
FApps can use other apps as content providers
FVery powerful emulator to develop on, integrated withEclipse IDE or Android Studio.
FMIT has the AppInventor2 site – interesting way to getstarted
FBattle for dominance between iPhone and Android?
–Anybody else in the running?