Introduction to Android Development with Java

INTRODUCTIONTO
ANDROID DEVELOPMENT
Jim McKeeth
@JimMcKeeth
jim@mckeeth.org
1
Tuesday, August 20, 13

AGENDA
• Hello Android
• Overview of Platform
• PlatformTools
• UI - XML
• Views & Widgets
• Architecture
• Manifest & Permission
• Activities & Intents
• Debugging
• Resources
2

ABOUT ME
• Live here in Boise - jim@mckeeth.org
• Lead Developer Evangelist for EmbarcaderoTechnologies
• www.embarcadero.com - Delphi for Android coming soon
• Google Developer Group - www.gdgb.org
• Boise Software Developers Group - www.bsdg.org
• Boise Code Camp - www.BoiseCodeCamp.com

DEMO: HELLO ANDROID

GOOD PLACESTO KNOW
• developer.android.com - Ofﬁcial developer site
• developers.google.com/android/ - Google on Android
• developers.google.com/events/io/ - Google I/O Replays
• stackoverﬂow.com - Great Q&A community
• android.stackexchange.com - End user Q&A
• vogella.com/android.html - Detailed tutorials
5

ANDROID
6

ANDROID STACK
• Tweaked Linux 2.6
• Tweaked Java (Dalvik)
• Android OS
• Android Apps
• (Mostly open source)
7

VERSION HISTORY
• November 5th, 2007 is Android’s Birthday
• Each version has a version number, name and API level
• Version number is most speciﬁc
• Name is group of versions and API levels
• Latest:Android 4.3 Jelly Bean (API 18)
http://en.wikipedia.org/wiki/Android_version_history#Version_history_by_API_level

VERSION POPULARITY
As of August 2013
http://sn.im/platform-versions9
40% = Jelly Bean
63% >= ICS
96% >= Gingerbread
40%
23%
33%

ARCHITECTURE
http://sn.im/what-is-android
11

FRAMEWORK
• DalvikVM
• WebKit Browser
• 2d Graphics Library, 3D w/OpenGL
• SQLite
• MPEG4, MP3, PNG, JPEG, etc
• GSMTelephony, Bluetooth,WiFi
• Camera, GPS, Compass,Accelerometer
12

CORE APPLICATIONS
• Phone
• eMail and SMS clients
• Calendar
• Contacts
• Web Browser
• Geographic Support via Google Maps
13

ANDROID DEVELOPMENT

ANDROID SDK
• http://developer.android.com/sdk
• 3 Options
• ADT Bundle (in Eclipse)
• “Existing IDE” download
• Android Studio preview (in IntelliJ)
15

RELATEDTOOLS
• Managers
• Android SDK Manager
• AVD Manager (AndroidVirtual Device)
• Command-LineTools
• adb (Android Debug Bridge -Your best friend!)
• Others

ANDROID DEVELOPMENT
JDK$
Android'
SDK'
Dalvik'
Virtual'
Machine'
Linux&
kernel&

BUILD PROCESS
Android'App'Package'
APK'
DEX'Compiler'
Dalvik'byte'code'
Java'Compiler'
Java'JAR'

THE APK FILE
• Zip ﬁle containing
• Manifest, etc.
• Compiled code
• Resources & Assets

ACTIVITY ARCHITECTURE

Applica'on*Context*
PARTS OF AN ANDROID APP
Intent%
Ac#vity(
Class% Layout' String'
Resources'
Android'
Manifest'
Other&
Classes&
Drawables)
Services(
Broadcast)
Receiver)
Content&
Providers&
Ac#vity( Intent%

PROJECT LAYOUT
• AndroidManifest.xml
• bin (APK file, compiled DEX files)
• gen (generated resources)
• res (resources you create)
• src (Java source files)

MANIFEST
• Mandatory XML ﬁle “AndroidManifest.xml”
• Describe application components
• Default Activity
• Permissions,Attributes
• Non-SDK libraries
http://sn.im/android-manifest

MULTIPLE ACTIVITIES
• Each Activity must be deﬁned in manifest by class name and
“action”
• Activities reside on a “task stack” - visible activity is “top of
stack”
• Transition to an Activity using Intent
• Return from Activity using Activity.ﬁnish() which pops off task
stack

“RES” - RESOURCES
• XML Files
• drawable
• layout
• values
• etc.
• Graphics

RES/LAYOUT
• Each Activity should have dedicated layout XML file
• Layout file specifies Activity appearance
• Several layout types
• Default LinearLayout provides sequential placement of widgets

RES/VALUES
• strings.xml contains String constants
• Prefer strings.xml to hardcoded values (warnings)
• L10N/I18N (Localization/Internationalization)

• Application/Task is a stack of Activities
• Visible activity = top of stack
• Activities maintain state, even when notTOS
• “Back” button pops stack.
• “Home” key would move stack to background
• Selecting application brings to foreground or launches
new instance
APPLICATION AKATASK

ANDROID.APP.ACTIVITY
• Activity extends Context
• Context contains application environment
• “a single focused thing a user can do”
• An application consists of 1 or more Activities
• Provides a default window to draw in, might be smaller than
screen or ﬂoat on top of others
• UI elements are “View(s)” or widgets

ANDROID.VIEW.VIEW
• Extends java.lang.Object
• Basic building block for UI components
• Rectangular area on display
• Responsible for drawing and event handling
• View is the base class for widgets

Callback Methods
(delegates)
Major States
Activity
Lifecycle
http://sn.im/android-activity

SAVING STATE

FRAGMENTS
http://sn.im/android-fragments

ANDROID.CONTENT.INTENT
• Interprocess Communication messaging
• Can launch an Activity or start a Service
• new Intent(String action, Uri uri);
• new Intent(Context packageCtx, Class class);
• Intent.putExtra()
• Intent.setAction()
http://sn.im/android-intent

INTENT (CONTINUED)
• android.intent.action.MAIN (receiver on main activity)
• many options:ACTION_VIEW, etc
• category = extra information
• MIME type
• extras (i.e. getAction(), getExtra(), etc)

INTENT USAGE
• Activity Switch:
• new Intent(this, NextActivity.class);
• Web Browser:
• Uri uri = Uri.parse(“http://foobar.com”);
• new Intent(Intent.ACTION_VIEW, uri);
• Phone Dialer:
• Uri uri = Uri.parse(“tel:4085551212”);
• new Intent(Intent.ACTION_VIEW, uri);
http://sn.im/android-intent

VIEW LISTENERS
• GUI is event driven
• Event source: button press, mouse click, etc.
• Listener catches event and performs action
• Events are delivered to view w/current focus

EVENT LISTENER
• onClick()/View.OnClickListener()
• (boolean) onLongClick()/View.OnLongClickListener()
• onFocusChange()/View.OnFocusChangeListener()
• (boolean) onKey()/View.OnKeyListener()
• (boolean) onTouch()/View.OnTouchListener()
• onCreateContextMenu()/
View.OnCreateContextMenuListener()
• return true to stop event propagation

VIEW SIZE
• FILL_PARENT = parent sized (minus pad)
• Now “MATCH_PARENT” w/API Level 8
• WRAP_CONTENT = just big enough (plus pad)

LAYING OUTVIEWS
• Gravity = position (i.e. left, right, center)
• Weight = extra/empty space allocation
• priority for expansion
• default weight is zero

DIMENSIONVALUES
• Dimension values:
• dp/dip = density independent pixels
• sp = Scale independent pixels
• px = pixels
• in/mm = inches/millimeters
• pt = point (1/72 inch)
RecommendedNotRecommended

DENSITY INDEPENDENT
PIXELS
• An abstract unit that is based on the physical density of the screen.These units
are relative to a 160 dpi (dots per inch) screen, so 160dp is always one inch
regardless of the screen density.
• The ratio of dp-to-pixel will change with the screen density, but not necessarily
in direct proportion.
• You should use these units when specifying view dimensions in your layout, so
the UI properly scales to render at the same actual size on different screens.
• The compiler accepts both "dip" and "dp", though "dp" is more consistent with
"sp".

SCALE-INDEPENDENT PIXELS
• This is like the dp unit, but it is also scaled by the user's font
size preference.
• Recommend you use this unit when specifying font sizes, so
they will be adjusted for both the screen density and the
user's preference.
Recom
m
ended
for
Fonts

COLORS
• #RGB
• #ARGB ( Alpha / Red / Green / Blue )
• #RRGGBB (i.e. #3d1ec4)
• #AARRGGBB

VIEW /VIEWGROUP

LAYOUTS (VIEWGROUPS)
• AbsoluteLayout -Absolute X,Y (depreciated)
• FrameLayout - Pinned to top left (simplest)
• LinearLayout - Horizontal orVertical - one per row
• RelativeLayout - Child specify relative widgets
• SlidingDrawer - Hides until dragged out by handle
• TableLayout - Rows & Columns
• ScrollView - Child can be larger than window
• TabWidget - Manages collection of “Tab Hosts”

ORIENTATION
• landscape or portrait
• dedicated layout ﬁle
• /res/layout = default layout directory
• /res/layout-land = landscape layout directory
• /res/layout-port = portrait layout directory

DEMO - LAYOUTS &VIEWS

TRACE LOGGING
• android.util.Log
• Log.d(“tag”,“debug”);
• Log.e(“tag”,“error”);
• Log.i(“tag”,“informational”);
• Log.v(“tag”,“verbose”);
• Log.w(“tag”,“warning”);
• View output using “adb logcat”
http://sn.im/android-log

ADB - ANDROID DEBUG
BRIDGE
• Manages devices & emulators
• Issue debug commands
• Log output (adb logcat)
• Shell (adb shell)
• Copy ﬁles to/from emulator (adb push/pull)
http://sn.im/android_debug_bridge

DEMO - ADB & LOGCAT

BEST PRACTICES

BEST PRACTICES
• Support multiple screen sizes and densities
• Use the Action Bar pattern - Good-bye menu button
• Build Dynamic UI with Fragments
• Know when to persist and restore state
• Don’t block main thread - use AsyncTask -Test with
StrictMode
http://sn.im/android-practices
http://sn.im/android-performance

SUPPORT MULTIPLE SCREENS
SIZES & DENSITIES
• Use wrap_content, ﬁll_parent, or dp units when
specifying dimensions in an XML layout ﬁle
• Do not use hard coded pixel values in your
application code
• Do not use AbsoluteLayout (it's deprecated)
• Supply alternative bitmap drawables for
different screen densities
• ldpi, mdpi, hdpi, xhdpi
http://sn.im/android-screens

SCREEN SIZES & DENSITIES

ACTION BAR
1. App Icon - optional “up” affordance
2. View control - Navigation
3. Dynamic number of “important” action buttons
4. Action overﬂow
http://sn.im/android-actionbar
http://actionbarsherlock.com/

ASYNCTASK
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) {
int count = urls.length;
long totalSize = 0;
for (int i = 0; i < count; i++) {
totalSize += Downloader.downloadFile(urls[i]);
publishProgress((int) ((i / (float) count) * 100));
// Escape early if cancel() is called
if (isCancelled()) break;
}
return totalSize;
}
protected void onProgressUpdate(Integer... progress) {
setProgressPercent(progress[0]);
}
protected void onPostExecute(Long result) {
showDialog("Downloaded " + result + " bytes");
}
}
http://sn.im/android-asynctask

STRICT MODE
• Place a policy on a thread - provides feedback when blocked
public void onCreate() {
if (DEVELOPER_MODE) {
StrictMode.enableDefaults(); // Or configure
}
super.onCreate();
}
• http://sn.im/android-strictmode
• http://sn.im/android-strictmode-blog

GOOD PLACESTO KNOW
• developer.android.com - Ofﬁcial developer site
• developers.google.com/android/ - Google on Android
• developers.google.com/events/io/ - Google I/O Replays
• stackoverﬂow.com - Great Q&A community
• android.stackexchange.com - End user Q&A
• vogella.com/android.html - Detailed tutorials
61

Introduction to Android Development with Java

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