Intro to Android Development
Written by Keren Kalif, Edited by Liron Blecher
Contains slides from Google I/O presentation
© Keren Kalif
Content
•
Android development environment
•
Android project structure
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Example with threads
•
Example with networking
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Android Development Tools
The Android Development Tools (ADT) is a collection of
classes and utilities needed to develop for Android
It’s basically Eclipse + Android SDK + Android Plugin for
Eclipse
Download the SDK from: http://developer.android.com
Extract the zip file into a folder on your hard drive
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Android Emulator
The Android emulator is a software that runs the
Android OS on your local (Windows) OS.
Go into the Android SDK directory and run the program
Manager.exe
The Manager will enable you to create Android Virtual
Devices on your system.
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Android Virtual Device Manager
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Android Virtual Device Manager – cont.
Name of the device
Android Version
Memory on the device
Screen Type (affects resolution)
Additional Hardware
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Running the Emulator
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Create a new Android Project
Go to File  New  Project  Android Project
Project Name
Android OS Version
Application Name
Package Name (must
have at least two levels)
Startup Activity
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The created project
This is the top
“frame” of the project
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What is an Android Application
An Android application is actually a
collection of several components, each
defined in AndroidManifest.xml
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Anatomy
ofan
anApp
App
Anatomy of
•
•
•
•
•
•
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Activity
Service
Content Provider
Broadcast Receiver
Intents
Manifest
Anatomy of an App - Activity
• A single screen with a user interface
• Independent but work together to form
a cohesive whole
• Possible to invoke from other
applications
• Extends the Activity class
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Anatomy of an App - Service
•
•
•
•
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Perform long-running operations in the background
Does not provide a user interface
Other components can bind/interact
Extends the Service class
Anatomy of an App - Content provider
• Manages a shared set of application data
• Consistent interface to retrieve/store data
o
o
RESTful model
CRUD operations
• Can be backed by different stores
o
e.g. File System, SQLite DB, Web
• Can expose your data to other applications
• Can consumer data from other Content Providers
o
e.g. Contacts or Call Log
• Extend the ContentProvider class
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Anatomy of an App - Broadcast receiver
• Respond to system wide messages
• Messages can be initiated by the system or an app
• 2 type of broadcast:
o
o
Normal - delivered async to all receivers
Ordered - delivered in priority order & can be aborted
• Can programatically register or statically register via the
manifest
• Should be very light, pass any work onto a Service
• Extend the BroadcastReceiver class
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Anatomy of an App - Intents
• Intents are the messages that link app
components together
• Explicit / implicit
• An abstract description of an operation to be performed
o
o
o
An Action to be performed
The Data to operate upon
Extra metadata
• Standardise on a common vocabulary of Actions
o
e.g. 'View', 'Edit', 'Send'
• Apps register their ability to handle Actions for a given data
type via IntentFilter
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Anatomy of an App - Intents
• Publish an 'Intent API'
o
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Specify Action & Extras to invoke your component
Anatomy of an App - Intents
• Achieve complex tasks by calling other Application's
Intents, e.g. scanning a barcode
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Anatomy of an App - Activity lifecycle
• Running in a multitasking environment
• Users switch apps, calls come in,
system runs low on memory
• System invokes callbacks in your app
• The system will kill your app
• Be sure to save state!
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Anatomy of an App - Activity lifecycle
Activity
created
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Anatomy of an App - Activity lifecycle
Activity
created
onCreate()
onResume()
Activity
running
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Anatomy of an App - Activity lifecycle
onResume()
Activity
running
Call comes
in
onPause()
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Anatomy of an App - Activity lifecycle
onResume()
Activity
running
Call comes
in
onPause()
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Return to
app
Anatomy of an App - Activity lifecycle
onResume()
Activity
running
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Activity
destroyed
Call comes
in
Low
Memory
onPause()
Return to
app
Resources
In Android, anything that is not pure code is written in a
separate resource file (not a java file), for example
strings, images, etc.
This separation enables easier multi-language support
since only the resource file needs to be changed –
not the code itself
Resource files are saved as XML file and the Resource
Complier generates a Java file which reference the
data in these XML files.
The generated Java file is called R.java
Using this file you can access the data in java code
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Resources – cont.
Resources live in the res folder
Qualifiers provide specific resources for different device
configuration
e.g. layout-land, drawable-hdpi
Resources IDs automatically generated in R.java
e.g. R.layout.main
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Resources – cont.
When creating UI elements in Android,
the components and their layout are
saved in an XML file
The Android compiler generates the
R.java file under the “gen” folder
Whenever a new resource is changed,
the R file will be re-generted
‫(משאבים‬Resources)
main.xml
main.xml contains the layout in a form
of XML declaration.
It will be used in setContentView
Resources – cont.
Resources – cont.
main.xml defines all the components that will be
displayed in the activity
Each view will have its own ID in order to be able to
access it directly
strings.xml defines all the strings in the system
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Views
In Android, all UI elements are Views (or inherit from the
View class) – it’s kind of like JComponent in Swing.
The Activity class has a method called setContentView
which sets the View that will be displayed in the
Activity.
The XML file is translated into a View instance
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Permissions
Each Android application must declare what external
actions/resources its going to access (GPS, address
book, phone, etc)
Required permissions are declared in the manifest.xml
file.
To be able to access the internet:
AndroidManifest.xml:
• To allow an Android application access to the internet, add the
following tag under the permissions tag:
<uses-permission
android:name="android.permission.INTERNET" />
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Default Activity
You can define the default Activity in the manifest.xml
file
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Accessing localhost of the host machine
Since the Android emulator runs as a virtual machine,
trying to access localhost or 127.0.0.1 will direct you
to the Android VM, and not your host machine (your
computer)
To access your host machine from within the Android
VM, use the IP address: 10.0.2.2 (example:
http://10.0.2.2:8084/chat)
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Toast - Popups replacement
To show a popup use: Toast.makeToast(…).show()
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Switching to another Activity
Each Activity is like a card with a specific logic to
handle.
To switch to another Activity (for example, when a user
click a login screen):
Intent myIntent = new Intent(view.getContext(),
Activity2.class);
startActivityForResult(myIntent, 0);
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Installing an Android Application
Under the “dist” directory in your project there will be a
*.apk file (which is like a war file or jar file = zip file
with a different extension)
Send this file as an email attachment and that’s it!
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Links
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Intro: http://www.io-bootcamp.com/sessions#TOCAndroid
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http://developer.android.com/sdk/installing.html
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http://developer.android.com/guide/index.html
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http://www.vogella.de/articles/Android/article.html
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http://thenewboston.org/tutorials.php
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http://www.androidhive.info/
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http://blog.js-development.com/2009/10/accessinghost-machine-from-your.html
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Last Thing…
iblecher@gmail.com