androidpres-131017065017-phpapp02

8/13/2019 androidpres-131017065017-phpapp02

1/62

Introduction to Android

Development

Owain Lewis

[email protected]@Ow_Zone
mailto:[email protected]:[email protected]


2/62

Goals of this session

Give an overview of the Android Ecosystem

Explain the core components of an Android

App

Drink beer

Create a simple working Android Application

Drink more beer


3/62

Order of Service

Part 1:

Introduction to Android Development (45mins)

Beer Break

Part 2:

Live Coding(45mins - or until it compiles)

Socialise


4/62

Android VM != JVM

Android Apps are:

Written in java (mostly)

Converted to .dex files

Compiled to bytecode

Run on the Dalvik VM


5/62


6/62

Whats inside an App

Compiled Java source code

Library dependencies e.g. MIME type lib

XML FilesUI layouts, fragments etc. Images, sounds, videos etc.

AndroidManifest.xml


7/62

Application Security

Each App is assigned a user in Android linux Each linux process has its own VM

Each Application runs in 1 process.

Applications can request permissions to

system resources etc. - but user must agree.


8/62

App Fundamentals: UI


9/62

App Fundamentals: UI


10/62

UI Design... Wrong talk


11/62

Application Resources

Additional files and static content that your

code uses

Layouts for different types of devices and

device orientations.

Images for different screen sizes and densities

Referenced by unique ID within code

Allow easy localization


12/62

Application Components


13/62

ApplicationManifest.xml

Defines application components

Identifies required permissions

Defines required API level Definers hardware/software features required

API libs to link against (e.g. maps API)

Components not in the manifest arent usable


14/62

Application Components


15/62

Intro to Activities

Single screen with UI

Multiple activities exist in same app

Activities work together but each is standalone

Any app can trigger any activity in any app (if

allowed)

More on that later


16/62

Intro to Services

Services generally run in the background

Perform work that a user isnt aware of

Multiple components can make use of arunning service

Example: GPS service, mp3 playing


17/62

Intro to Content Providers

Mechanism to allow apps to interact with data

Create, Query, Store, Update

Can store data in multiple ways File System, DB,network storage, or anywhere else the App can

get to.

Apps can query any Content Provider if they havepermission


18/62

Intro to Broadcast Receivers

A listener for system wide events

No UI component

Tend to be lightweight and do little work Example: Low battery handler


19/62

Intro to Intents

Intent binds components to each other at

runtime (e.g. Event mechanism)

Explicit Intent = message to activate specific

component by name

Implicit Intent = message to activate type of

component

Components define which Intent Types they

pick up with Intent Filters


20/62

Component Interoperability

Any app can start any other apps component e.g.

use the camera app activity to capture pictures

Don't need that code in your app

Components run in the process of the holder app (e.g.camera take pic activity runs under camera process).

Android apps don't have single entry point (main

method)

Activating a component in another app is not

allowed by system permissions - so use Intent.


21/62

Activating Components

Activity: pass Intent to startActivity()

startActivityForResult()- gets a result

Service: pass Intent to startService()or

bindService()if running already

Broadcast: pass Intent to sendBroadcast(),

sendOrderedBroadcast()sendStickyBroadcast()

Content: call query()on a ContentResolver


22/62

Make sense so far?


23/62


24/62

ActivitiesStates

Resumed/Running: up front and has focus

Paused: Another Activity is on top of this one -

but this is still visible.

Stopped: Backgrounded - still alive, not

attached to window manager

The OS can kill activities without focusbut

will restart if possible.


25/62

Activities - Lifecycle


26/62

Activities

Must be declared in Manifest

Can declare IntentFiltershow other apps can

use the activity

E.g. Action=MAIN and Category=LAUNCHER

tells Android this can be launched.


27/62

Activities - Manifest


28/62

ActivitiesStarting

Explicit Intent to start Activity:Intent intent = new Intent(this, SignInActivity.class);

startActivity(intent);

Implicit Intent to start Activity:Intent intent = new Intent(Intent.ACTION_SEND);intent.putExtra(Intent.EXTRA_EMAIL, recipientArray);

startActivity(intent);

Need a result? Call startActivityForResult()then implement onActivityResult()callback

Get the result in an Intent


29/62


30/62

Activities - Advanced

Fragments

Sub Activity with own lifecycle

Can be an invisible worker

Loaders (3.0 +)

Async pull data into Activity Views


31/62

Services

Long running operations - no UI. e.g. play music

Service can run forever, but should know how tostop itself

Started service = runs in background - does it'sown thing until it stops

Bound service = allows interaction/feedback.Destroyed when all components unbind.

Determine type of Activity by implementingcallbacks


32/62

Services - Callbacks

onCreate()

onStartCommand() onBind()

which returns IBinder = the defined interface for

comms.

onDestroy()


33/62

ServicesStart/Stop

startService(Intent)

stopSelf()

bindService (Intentservice, ServiceConnectionconn, int flags)

System destroys bound servicewhen clientsdisconnect.

Note that system can kill service without warning - butwill restart it
http://developer.android.com/reference/android/content/Intent.htmlhttp://developer.android.com/reference/android/content/ServiceConnection.htmlhttp://developer.android.com/reference/android/content/ServiceConnection.htmlhttp://developer.android.com/reference/android/content/Intent.html


34/62


35/62

Services - Manifest

Must declare all services in your

application's manifest file.

Supports IntentFilters and permissions.


36/62

Services - Threads

Services use the Main UI threadthis is bad.

Your service should create threads it needs to

handle work

If you want to handle multiple thread

simultaneously you need to manage this here.

You need to manage stopping the thread too

Alternative is to extend IntentServiceoffersworker per requestone at a time.


37/62

Services - IntentService

Creates a default worker thread that executes all intentsdelivered to onStartCommand() separate from yourapplication's main thread.

Creates a work queue that passes one intent at a time toyour onHandleIntent() implementation, so you never haveto worry about multi-threading.

Stops the service after all start requests have beenhandled, so you never have to call stopSelf().

Provides default implementation of onBind() that returns

null. Provides a default implementation of onStartCommand()that sends the intent to the work queue and then to youronHandleIntent() implementation.


38/62


39/62

ServicesUser Comms

Services can communicate with the user in a limitedway.

Once running, a service can notify the user of eventsusing Toast Notificationsor Status Bar Notifications.

Toast notification is a message that appears on thesurface of the current window for a moment thendisappears.

Status bar notification provides an icon in the statusbar with a message, which the user can select in orderto take an action (such as start an activity).
http://developer.android.com/guide/topics/ui/notifiers/toasts.htmlhttp://developer.android.com/guide/topics/ui/notifiers/notifications.htmlhttp://developer.android.com/guide/topics/ui/notifiers/notifications.htmlhttp://developer.android.com/guide/topics/ui/notifiers/toasts.html


40/62

Services- Advanced

Messengers

AIDL


41/62

Broadcast Receivers

Component that responds to system-wide

broadcast announcements

Many broadcasts originate from the system

Register for intents via Manifest

Meant to do very little work


42/62

Broadcast Receivers

Receiving a broadcast involves:

Registering receiver in Manifest or dynamically

Implementing: onReceive(Context, Intent)


43/62

Broadcast Receivers

Normal broadcasts: Context.sendBroadcast()

Asynchronous.

All receivers of the broadcast are run in an undefinedorder, often at the same time.

Ordered broadcasts:Context.sendOrderedBroadcast()

Delivered to one receiver at a time.

Each receiver executes in turn, and can propagate aresult to the next receiver, or abort the broadcast sothat it won't be passed to other receivers. Similar toFilters in JEE


44/62

Content Providers

Manage secure access to data - across process

boundaries

Don't need one if you're just providing data to

own app

Use ContentResolver to access data in a

ContentPtorvider

-Android includes ContentProviders forcontacts, audio, video, images etc


45/62

Content Providers

Data can be file (video etc) or Structured (tabular)

Data is provided as tables (similar to relational dbs)with primary keys (if needed)

Content is referenced using a URI scheme

e.g. content://user_dictionary/words

Need to ask for permission to use a provider - this is donein the manifest

Define a query to perform against the URI.

Returns a Cursor

Cursor can be wrapped in a CursorAdaptor and bound to aUI element.


46/62

Content Providers - Query


47/62

Content Providers

Also can insert, update and delete.

Batch access = process lots of data at a time

Contract Classes = Constants used in accessing

a ContentProvider.


48/62

Content Providers


49/62

Intent and IntentFilter

Activities, Services and Broadcast receivers are activated throughIntents

Intent is a passive bundle of information. OS figures out how to getit to the correct place.

Intent is:

Optional component name Action (e.g. ACTION_BATTERY_LOW) - you can invent your own

Data - URI of data and MIME type

Category - type of Intent (e.g. CATEGORY_LAUNCHER)

Extras - key/value pairs

Flags - how to deal with the intent

Explicit Intent = named

Implicit Intent = category of intents


50/62


IntentFilter tells the system which typeof

Intent a component can handle

Component can specify multiple filters

Filter has fields that parallel the action, data,

and category fields of an Intent object

Intent must match all 3 fields to be delivered

Note that Intent may not specify a field


51/62

IntentFilter Matching

Action: Intent action must match at least one Filteraction. Intent can leave action blank and match

Category: Every category in the Intent object mustmatch a category in the filter. Filter can list additional

categories, but it cannot omit any that are in theintent.

android.intent.category.DEFAULT must be implimented

Data:

No data = match

More complex rules for data matching if specified


52/62

IntentFilter Matching

Multiple filter match: Ask the user


53/62



54/62


55/62

Processes and Threads


56/62

AsyncTask

AsyncTask allows you to perform asynchronouswork on your user interface. It performs theblocking operations in a worker thread and thenpublishes the results on the UI thread, withoutrequiring you to handle threads and/or handlersyourself.

Subclass AsyncTask and implement:

doInBackground() onPreExecute, onPostExecute(), onProgressUpdate()

Run Task from UIThread by calling execute()


57/62

AsyncTask


58/62

Development Tools

Android Platform + SDK

Android Developer Tools (ADT) for Eclipse

Android Studio - Based on IntelliJ IDEA

Currently in Early Access release

Uses Gradle

Emulators and Hardware debugging


59/62

Questions?


60/62

Beer!


61/62

Live Coding


62/62

Introduction to Android

DevelopmentOwain Lewis

[email protected]@Ow_Zone
mailto:[email protected]:[email protected]

androidpres-131017065017-phpapp02

Documents