Download IFS234-Lecture6-AndroidDay1

Android Programming
Day 1
25 best Android Apps
http://www.youtube.com/watch?v=mLHqAMBQ
Lzo&feature=fvwrel
Java…a blast from the past
• Android development language is Java
• Java originally built as a cross platform
language
• Java should work on tv’s, music systems, etc.
• The hardware abstraction problem remained
• 2009 - 2012: Finally something like the
purpose Java was developed for is happening
through Android
Day 1
Then and now
• Android Inc bought by Google in 2005
• 2007 Open Handset Alliance
• 2008 – 2010 Android becomes dominant
mobile platform
• 2011 Games, Tablets
• 2012 Other devices (home entertainment)
Android versions
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2.3 Gingerbread
3 Honeycomb (API 13)
4 Ice Cream Sandwich (API 14)
5 JellyBean
developer.android.com
The Android Stack
The Stack – bottom layer
• Linux Kernel
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Not Linux
Hardware abstraction layer
Memory management
Process management
Networking
• Why Linux? Driver model well known…can make
it work on different chipsets
• Linux kernel is secure
• The adb shell command opens Linux shell
Native Libraries
• Pieces borrowed from other open source
projects
• Bionic, a fast and small c library, but under a
lgpl licence
• SQLite
Dalvik
• Android’s replacement for the Java Virtual
Machine
• Java VM owned by Oracle…licencing
• Easier on the battery
• Cooling effect
• CPU capabilities
• JVM…finds class file on disk…loads into RAM
• Mobile…no disk….so no need to load into RAM
Java VM
• A Java virtual machine is a program which executes certain
other programs, namely those containing Java bytecode
instructions. JVMs are most often implemented to run on
an existing operating system, but can also be implemented
to run directly on hardware. A JVM provides an
environment in which Java bytecode can be executed,
enabling such features as automated exception handling,
which provides root-cause debugging information for every
software error (exception), independent of the source
code. A JVM is distributed along with a set of standard class
libraries that implement the Java application programming
interface (API). These libraries, bundled together with the
JVM, form the Java Runtime Environment (JRE).
Java vs Dalvik
Application Framework
• The rich set of system services wrapped in an
intuitive Java API
• This is the environment/ecosystem that you as
a developer will tap into when writing Android
apps
• Location / Web / telephony / Wifi / Bluetooth
/ notifocations / media / cameras / etc.
Applications
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Dalvik executable (Java) + Resources = APK
Code + everything else = APK
Native libraries?
Must be signed
Markets
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Google Playstore
Amazon Android Market
Samsung Store
Many small stores now emerging
Other emerging Market
Questions about stack?
Installing Android
• Android SDK
• Eclipse (Helios / Indigo / Juno…)
Android SDK
• Folder (android-sdk)
– Tools
– Platform tools
• adb
• SDK Manager
– Install the platform you are going to use
Add Android Tools to Eclipse
• Help > Install new software >
• ADT Plugin - http://dlssl.google.com/android/eclipse/
• Windows > Preferences > Android > SDK
Location
Hello World!
• New Android Project
• Select target – which platform are you
targeting?
JAVA CODE
RESOURCES
MANIFEST
Resources
• Specific folders and files
• You cannot create your own folders in the
“res” folder
• Use the system to create new resource folders
and files when needed
• Strict naming convention
AndroidManifest.xml
• Used during the installation of your app
• Example…
• How to define an activity in your
AndroidManifest.xml file?
– Look at this in detail when working through xml
example.
Strings.xml
What about adding another language string.xml file > New > Android XML file
> strings.xml > Qualify
Activity_main.xml
• Screen layout view
Resources
• Summarized in R.java
• R.java is the glue between your java files (src)
and your resources (res)
• Do not look into it, or modify it!!
• Let’s just have a quick look at R.java
How do we use R to specify
resources?
How to run our App?
• AVD: Android Virtual Devices
– Emulator
– Emulator button in Eclipse
• Running on actual Android device
– Windows >> Kies
– Androidscreencast.jnpl
– Can save you lots of time!!
• Build Automatically must be activated
– Project > build automatically
Looking at the files
• How is the APK file built?
• Classes.dex + resources.ap_ = HelloWorld.apk
• This happens every time you build
• Look at these files in workspace folder now.
How to sign
• Keytool part of JDK…
• http://developer.android.com/tools/publishin
g/app-signing.html
• http://developer.android.com/tools/publishin
g/preparing.html
• Right-click on project
– Android tools
– Export signed application package
Command line – keystore gen
keytool -genkey -v -keystore my-release-key.keystore
-alias alias_name -keyalg RSA -keysize 2048 -validity 10000
jarsigner -verbose -sigalg MD5withRSA -digestalg SHA1 -keystore my-releasekey.keystore
my_application.apk alias_name
zipalign -v 4 your_project_name-unaligned.apk your_project_name.apk
DDMS perspective
• Windows > Open perspective
• DDMS
– File Explorer
– Emulator or device must be running…
– Check file structure (eg.look at system folder)
Main Building Blocks
Activities
• An activity represents a screen or a window
• Main activity
• Other activities
Activity lifecycle
• Activities have a well-defined lifecycle. The
Android OS manages your activity by changing
its state.
When to start/stop processes
• Expensive processes should not run in an
Activity (window) while it is not visible – this
uses unnecesary memory and cpu
• Start expensive processes (GPS, data
send/receive) in the onResume() method, and
stop them in onPause()
• This way they never run in an Stopped Activity
(window)
Intents – joining activities (screens)
• Intents represent events or actions