15-05-2012, 10:42 AM
An Introduction to Android for Developers
An Introduction to Android.pdf (Size: 2.09 MB / Downloads: 74)
Introduction Goals
•Get you Started with Android Development
•Get the Environment Set Up and Working
•Create Some Demo Apps (Tutorials)
•Demonstrate the Tools / Environment
•Introduction to the Documentation
•(Which is changing...)
•Build Enthusiasm (you can do it)
•Differences from Other Environments
• UI - Declarative XML Layout
• Activities
• Intents / Intent Receivers
• Services
• Content Providers
• Application Life Cycle
•Project Structure
• Files, Resources, Building
Tools
•SDK
• Command line tools (adb, aidl, etc.)
• Supporting Libraries
•IDE (We will use Eclipse)
• Eclipse Plugin
• Included:
• Debugger
• Profiler
• Resource Building
• Deployment
Not Covered
•Java Development Basics
•Similarities to Other Environments
•Parts that Aren’t Ready
• Syncing etc.
•Anything We Can’t Get to in time!
•Get you going, not teach you everything
GUI Creation / Layouts
GUI Creation
•Different from
• Java Swing
• Java ME
•Layouts
• res/layout - XML Files Go Here
• Layouts - Can be Nested
•Strings / i18n
• res/values/strings.xml
• Deployment
•IDs / Lookup
• Used to Bridge Views / Java Code
• @+id/myname Syntax
•Resource Building
• Eclipse Plugin Builds into R.java
• Efficient Resource Creation / Representation
• Less Chance of Programatic Errors (Intellisense)
•XML Declarative Faster to Develop
Layout Basics
•Views
• Basic Building Blocks
• TextView, EditText, Button, ImageView,
Checkbox, Lists, etc
•Layouts
• FrameLayout : Each Child a Layer
• LinearLayout : Single Row / Column
• RelativeLayout : Relative to Parent / Other Views
• TableLayout : Rows and Columns - HTML like
• AbsoluteLayout : <x,y> Coords - Discouraged
•Layouts can be Nested
Layout Parameters
•Parameters Control Many Aspects
•Some are More Common:
• <android:layout_width> and
<android:layout_height>
• “wrap_content”, “fill_parent”, values...
• <android:layout_weight>
• Relative amount of available space to use
•Most are in the Docs
• Class Reference documentation most useful
When Things Go Wrong
•Android is still early-release software
•Most problems fall within two areas
• Build Problems
• R class not updated or running old code
• Look at console and problems pane
• Clean Build
• Communication breakdown to emulator
• Code not deploying, errors, debugger failure
• Use DDMS Reset ADB option
• Or: quit eclipse and emulator, adb kill-server
Hello World Demo
First Project with Eclipse
Layout Experimentation
Android Concepts
Activities
• Typically corresponds to one screen in the UI
• Can be faceless
• Can be in a floating window
• Can return a value
• Can be embedded
Intents & IntentFilters
• Intents: description of what you want done
• IntentFilter: what an Activity or
IntentReceiver can do
• Activities publish their IntentFilters in
AndroidManifest.xml
• Forward navigation is accomplished by
resolving Intents
• Caller calls startActivity(intent)
(or startSubActivity... )
• System picks Activity whose IntentFilter
best matches intent
• New Activity is informed of the Intent
IntentReceivers
• Respond to alarms and notifications
• Including those originating externally
• Will wake up your process if necessary
• System can broadcast intents: data connection,
phone state changed, etc
• Apps can invent and broadcast their own intents
• IntentReceivers can (should) start Services for
lengthy tasks (e.g. downloading new data)
• IntentReceivers can put up UI notifications
• Register IntentReceivers in AndroidManifest.xml
• Can also attach IntentReceivers to other
objects so they can receive notifications
(Activities, Views, etc.)
Services
• Faceless classes that run in the background
• Music player, network download, etc.
• Services run in your application’s process or
their own process
• Your code can bind to Services in your process
or another process
• Once bound, you communicate with Services
using a remotable interface defined in IDL
ContentProviders
• Enable data sharing across applications
• Provide uniform APIs to:
• query data (returns a Cursor)
• delete, update, and insert rows
• Hide underlying implementation
• Work across processes
ContentProviders
• All content is represented by URIs
• Convenience methods mean clients don’t
need to know syntax
• ContentProviders own URIs based on
authority, e.g. content://contacts/...
• ContentProviders are responsible for
mapping URIs they own to a MIME type
Quick Dial Code Walkthrough
Eclipse Import + Code
Walkthrough
Life Cycle & Bundles
Application Lifecycle
• Applications run in their own processes
• Many Activities, Services, etc. can run in
the same process
• Processes are started and stopped as
needed to run an application's components
• Processes killed to reclaim resources
Life Cycle of an Application
Activities
• Designed to be reused and replaced
• Your application can invoke Activities
from another application
• Another application can invoke your
Activities
• Existing Activities can be replaced with a
new Activity that fulfills the same contract
Activity Lifecycle
• An Application can have Several Activities
• Activities can be started with
• startActivity() - Synchronous
• startSubActivity() - Asynchronous, with handler
callback
• Each Activity has its Own Life Cycle
• Messages can be Passed with Bundles
• Like Services on a Bus
Bundles
• Similar in concept to a simple Map
• Can put data into Bundle under a name
• bundle.putString(“name”, <data object>)
• Can also be retrieved by name
• bundle.getString(“name”)
• Bundles used to pass messages/store state
• onFreeze() has outState bundle passed in
• Data stored in outstate handed back to
onCreate as the icicle bundle
Storage / Persistence
• Normally handled by ContentProvider
• Front end to File, DB, Online Service, etc.
• SQL Lite is Available to Developers
• Simple SQL DB
• Can also access flat files
• Online communication yet to be formalized
Note Pad Example
See the Tutorial in the SDK
Multi-stage exercise to illustrate
the basics.
Resources, Packaging and Security
Resources
•Added under the res/ folder
• layout, drawable, anim, values, xml, raw
• layout for declarative layout files
• drawable/anim for bitmaps, transitions, etc.
• values includes strings, arrays, colors,
dimensions, styles and more
• xml for general XML files available at runtime
• raw for binary files (e.g. sound)
•Compiled into the apk
• Read through API convenience methods
• e.g. XML access looks like a pull parser
Assets
•Similar to Resources, but...
• InputStream access to Assets
• Placed under assets folder
• Looks like a “root” folder to app
• Read only access
•Any kind of file
• Stored on device - watch the size
APK files
•Android Packages
• All class files and resources needed to run
• Class files recoded to dex
• Manifest defines activities and other facets
•DEX
• Dalvik Executable
• More compressed form than bytecode
• Third party libs can be converted to dex
•APK is the application
• Install - put APK in data/app
• Uninstall - remove APK
Security
•Unique Users for Apps
• App completely sandboxed
• Sharing only via ContentProviders, Activities,
IntentReceivers, Services, etc.
• Strong, linux-backed security
•Access to Restricted Features
• Must be declared in the Manifest
• Still working on rest of security model
• Some kind of trusted authority
• Advanced users should have fine grained control