Android development - the basics, MFF UK, 2014

Android Development - the basics

Tomáš Kypta

• Android platform and ecosystem"• Android SDK and development tools"• Hello World"• building blocks of Android apps & the

manifest file"• activities, widgets, intents"• toasts

Agenda

• Linux-based operating system"

• open-source (http://source.android.com/)"

• originally phone OS"

• tablet support (since Honeycomb, Android 3.0)

Android platform

• Google TV"

• Google Glass"

• Google Wear

Android platform

• 2003, Android inc."

• 2005, acquired by Google"

• Sep 2008, the first Android phone"

– T-Mobile G1"

• May 2010, Froyo (Android 2.2)"

• Feb 2011, Honeycomb (Android 3.0)

History

• Oct 2011, Ice Cream Sandwich (Android 4.0)"

• July 2012, Jelly Bean (Android 4.1)"

• July 2013, Jelly Bean (Android 4.3)"

• Oct 2013, KitKat (Android 4.4)"

• June 2014, Android L (developer preview)

History

Platform Versions

• thousands of devices"• the most popular mobile platform"• 1.5 million new devices activated every day"– Q2 2013"

• September 3, 2013, 1 billion Android devices have been activated"

• most devices made by Samsung "– 65%, Feb 2014

Android ecosystem

• apps are distributed by app stores"– Google Play, http://play.google.com"– other stores (Amazon, Samsung, …)"

• > 50 billion apps have been installed from Google Play"

• > 1.3 million apps

Google Play

• customers can purchase"

• developers can sell"

• Play Music "

• Play Books "

• Play Movies

Google Play

• selling apps"

– 15 min return period"

• in-app billing"

– freemium model"

• ads"

– AdMob, ...

Monetization

• fragmentation"• manufacturer/carrier enhancements"• updates & support"• openness - low quality apps in Google Play"• malware"– users

Android “problems”

• app can be installed directly"

– .apk file"

• user accepts app permissions when installing or updating the app

Android security

• Verify Apps (Android 2.3+)"

– checks every app install"

• Google Play can remotely uninstall harmful apps

Android security

• programming in “Java”"

– Java SE 7 (KitKat)"

• native apps possible (C++)"

• development tools platform friendly"

–Windows, Linux, Mac OS X

Development

• IDE support"

– Android Studio, IntelliJ IDEA"

– ADT plugin for Eclipse"

– Netbeans"

• you can freely develop on any device

Development

• android - Android SDK and AVD Manager"

• adb - Android Debug Bridge"

• monitor - (ddms & hierarchyviewer)"

• emulator"

• lint, Traceview, ProGuard"

• docs, samples

Android SDK

• compatibility libraries"– v4 - backports lots of newer functionality

to Android 1.6+"– Fragments, NotificationCompat, ViewPager"

– v7"– AppCompat"

– v8"– v13

Support Libraries

• Google Maps"

• In-app Billing"

• Games"

• Google+"

• Authorization

Google Play Services

• AdMob"

• Google Analytics, Flurry, Crittercism

Libraries

• Activity"

• Service"

• Content provider"

• Broadcast receiver"

• AndroidManifest.xml

Android building blocks

• screen with user interface"

• the only visual component"

• example - an email app"

– list of emails"

– details of an email"

– email composition

Activity

• has no UI"

• long-running tasks"

• examples"

–music playback service"

– download service"

– sync service

Service

• managers and shares application data"• data storage doesn’t matter (db, web,

filesystem)"• apps can query and modify data through

content provider"• r/w permissions can be defined"• examples - all system dbs (SMS,

contacts, ...)

Content Provider

• responds to broadcasts"• broadcasts are system wide"• can be registered statically or dynamically"• system or custom messages"• examples - incoming SMS, incoming call,

screen turned off, low baterry, removed SD card, BT device available, ...

Broadcast Receiver

• defines what parts the app have"

• defines which endpoints are exposed"

• minimum/maximum API level"

• permissions"

• declare hardware and software features"

• require configuration

AndroidManifest.xml

• asynchronous message"

• binds components together (all except Content Provider)"

• starting activities"

• starting services and binding to services"

• sending broadcasts

Intent

Hello World

Build

• a subclass of android.app.Activity"

• app usually has many activities"

• activities managed in activity stack"

– newly started activity is placed on the top of the stack

Activity

• activity can be in different states during its lifecycle"

– foreground, visible, stopped, killed"

• when activity state changes a system callback is called

Activity Lifecycle

• onCreate() - activity created"

• onStart() - activity visible for the user"

• onResume() - activity gains user focus

Activity callbacks

• onPause() - system resuming another activity"

• onStop() - activity becoming invisible to the user"

• onDestroy() - before activity is destroyed

Activity callbacks

• onRestart() - called if activity was previously stopped, called prior to onStart()

Activity callbacks

• when configuration changes, activities are destroyed and recreated"

– default behaviour, can be changed"

• properly handle config changes"– onSaveInstanceState(Bundle)

Configuration changes

• starting activity explicitly"– new Intent(context, MyActivity.class)!

• starting activity implicitly"– new Intent(Intent.ACTION_VIEW,

Uri.parse(“http://developer.android.com”))!

• starting activity for result

Intent & Activity

• defined by a hierarchy of views"

• layouts = containers"– LinearLayout, RelativeLayout, FrameLayout, ...

User Interface

• widgets"

– UI objects"

– Button, TextView, EditText, RadioButton, ..."

–WebView

User Interface

• list widgets"

– subclasses of AdapterView"

– display a list of items"

– use adapter to bind list do data"– ListView, GridView, Spinner, ...

User Interface

• provide data for Adapter views"

• are responsible for the creation of items

Adapters

• drawables"

– bitmaps"

– 9-patch png"

– state lists"

– layer lists"

– shape drawables

Resources

• layout"

• strings"

• colors"

• menus"

• dimensions"

• animations

Resources

• arrays"

• ids"

• raw"

• xml"

• ...

Resources

Screen sizes and densities

• How to handle different screen sizes and densities?

Screen sizes and densities

• resources can be created in several versions"

– the best version is selected according to current device configuration in runtime

Resources

• resource units"

– dp - density-independent pixel"

– sp - scale-independent pixel (for fonts)"

– never use px!!!

Resources

• suffixes for resource folders"

– drawables, drawable-mdpi, ..."

– values, values-cs"

– layout, layout-sw640dp"

– drawable-hdpi-v11

Resource qualifiers

• screen density - ldpi, mdpi, hdpi, xhdpi, ..."

• screen size - small, normal, large, xlarge"

• screen orientation - port, land"

• language - en, cs, sk, en-rGB…"

• version - v11, v14, ...

Resource qualifiers

• since Android 3.2"

• w<N>dp - available screen width, w600dp"

• h<N>dp - available screen heights, h720dp"

• sw<N>dp - smallest width (does not change with orientation)

Resource qualifiers

• accessed from code via generated R.java file and resource ids"– view.findViewById(R.id.txt_name)!

– txtName.setText(R.string.txt_name_label)

Resources

Localization?

• How to handle different API levels available on different devices?

Android version fragmentation

• build target"

– API level the app is compiled against"

• AndroidManifest.xml"– <uses-sdk android:minSdkVersion="8"

android:targetSdkVersion="16" />

Android version fragmentation

• handling versions in code"if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD) {!

! // code for Android < 2.3!

}

Android version fragmentation

private boolean functionalitySupported = false;!

static {!

try {!

checkFunctionalitySupported();!

} catch (NoClassDefFoundError e) {!

!functionalitySupported = false;!

}!

}!

private static void checkFunctionalitySupported() throws ! NoClassDefFoundError {!

! functionalitySupported = android.app.Fragment.class != null;!

}!

Android version fragmentation

• main thread = UI thread"

• do not ever block the UI thread!!!"

• use worker threads for time consuming operations"

• UI toolkit not thread safe - never manipulate UI from a worker thread

Threads

• java.util.logging.Logger

• android.util.Log

Logging

• simple non-modal information"• displayed for a short period of time"• doesn’t have user focus

Toast

SharedPreferences prefs = PreferenceManager!

! .getDefaultSharedPreferences(context);!

SharedPreferences prefs = !

! config.getSharedPreferences(PREFS_FILE_NAME,!

! Activity.MODE_PRIVATE);!

"int storedValue = prefs.getInt(SOME_KEY, defaultValue);!

"SharedPreferences.Editor editor = prefs.edit();!

editor.putInt(SOME_KEY, storedValue);!

editor.commit();

Preferences

• developer.android.com"• android-developers.blogspot.com"• source.android.com"• stackoverflow.com"• youtube.com/androiddevelopers"• svetandroida.cz

Sources

THE END