Intro to programming with Androids

@MaksimGolivkin

Android dev @Uber

Plan

•  Brave mobile world

• Daily life-cycle

• Different screens

• Hybrid applications

Why “mobile” development?

In developing world

And in the most posh economies.

Smartphones, tablets and more

Only an Internet device?

What smart devices are made of?

Memory Ports Positioning Radios Sensors Build-­‐in   Audio   Cellular   Mobile     Audio  

SD  card   USB   GPS   Wi-­‐Fi   Photo/video  

HDMI   Wi-­‐Fi   Bluetooth   Light  

A-­‐GPS   NFC   AcceleraBon  

MagneBc  

Gyroscope  

Proximity  

… Flash, Stylo, Second Screen

Dongle empowering 3 billion $ business

Why Android?

Android creates a sweet choice.

Open mobile computing platform

64% in smartphones

40% in tablets  

of device sales in 2012 Q3

Android accounts for

GooGPS show-case

Two big butts

• App profitability 1/6 of iOS

•  Fragmentation

Summary

• Dawn of connected devices era.

• HW knowledge creates opportunities.

• Android is leading it.

Android OS

Designed for fast switching between apps

Applications “talk” between each other

There is always a Back button

Programming Android

APIs

•  SDK – Java applications

• NDK – mostly games

• Hybrid – everybody should

Tools

•  Eclipse

•  Eclipse ADT plugin

• Android SDK

• USB drivers

Learn Android •  d.android.com •  stackoverflow.com

•  AppDemo sample application •  youtube for Google I/O

•  Android OS source code •  grepcode.com Books!

Script vs. Application

uber.com Init

Process

Output Display

Die PHP script life-cycle

Interact

Init

Process

Die

Display

State

Application life-cycle

Screen ~= Activity

Created

Resumed

Stopped

Launch

Press Home

Interact

Foreground In Memory

Created

Started

Resumed

Stopped

Launch

Paused

Interact

Open other

Activity

Visible Foreground In Memory

Started

Resumed

Stopped

Re-Launch

Press Home

Paused

Interact

Visible Foreground In Memory

Activities Stack (briefly)

1st Screen

Resumed 1.

2nd Screen

Stopped

Resumed

1.

2.

3rd Screen

Stopped

Resumed

Stopped

1.

2.

3.

Closes an application

Delegates responsibility

Pressing Back

Stopped

Resumed

Stopped

1.

2.

3.

Destroying last activity

Stopped

Resumed

1.

2.

Pressing Home

Stopped

Resumed

Stopped

1.

2.

3.

Stops everything

Stopped

Stopped

1.

2.

Stopped 3.

Returned to the app

Stopped

Resumed

Stopped

1.

2.

3.

Running In The Background?

… not all of them

Maintaining state

Activity/app life-time

• Parameters

+ Saved Instance State

•  Singleton

Singleton is king. Mind the GC!

Persistence

•  Shared Preferences

•  Files

•  Server

•  SQLite

Do you really need it?

Service

Use cases

•  Long actions in between activities

• Notifications, when app is dead

•  Intensive calculations

Consider simply using Threads. Twice!

Fragments

Fragments enable multi-pane layouts

Resources

Life of an image

Resources r = getResources(); Drawable d =

r.getDrawable(R.drawable.ic_american_express); ImageView icon =

(ImageView) findViewById(R.layout.card_logo); icon.setDrawable(d);

Using resources

Drawable vs. View

Screen ~= Activity Everything else ~= Views

Summary (Android OS) • Android is popular but poor, yet

•  Learn life-cycle by heart

• Assess feasibility of Persistence and

Services. Twice.

Many screens

Different resolutions

320x480 px 1280x720 px

42 dp

Same physical size

screen_ density = pixel _width2 + pixel _height2

diagonal _ in_ inches

Screen density

Many resolutions 320x426 legacy phones 240x320 legacy phones 320x533 320x576

legacy phones

320x480 phones 320x533 320x568

phones

320x480 360x640 400x640

new phones

640x1067 640x1138

tweener tablets

480x800 480x854

600x1024

tweener tablets

1024x768 1280x768 1280x800

tablets

...  

Landscape is yet another resolution

Patterns

Stretching

Adding margins

Multi-pane

Switch points

Switch points

small size portrait small size landscape normal size portrait

normal size landscape large size portrait

Home base 240dp 320dp 360dp 400dp 426dp 480dp 533dp 568dp 578dp 640dp

resized elements

margins added

switch point (another layout)

Expensive way

small size portrait small size landscape normal size portrait

normal size landscape large size portrait

Home base 240dp 320dp 360dp 400dp 426dp 480dp 533dp 568dp 578dp 640dp

Boom!

resized elements

margins added

switch point (another layout)

Prepairing graphics

Density buckets

ldpi (low) 100 ~ 140 dp

mdpi (medium) 140 ~ 200 dp

hdpi (high) 200 ~ 280 dp

xhdpi (extra high) 280 ~ 340 dp

1 dp = ? px

ldpi 0.75

mdpi 1

hdpi 1.5

xhdpi 2

Nine-patch

Resizable area

Content area

Nine patch •  Buttons

•  Backgrounds

Summary (Many screens) • Needs investment, but little surprise.

• One layout for a start.

• Resolution ignorance is ugly,

but not ineffective.

Hybrid apps

“Our biggest mistake was betting too much on HTML5”, - Mark Zuckerberg

HTML5 reality in 2012

Hybrid champion: LinkedIn

Native

Native

HTML/CSS  

Hybrid architecture

Native

JavaScript API

HTML/CSS/JavaScript

WebView webView = (WebView) findViewByid(R.id.webview);

webView.addJavascriptInterface(obj, "Android"); final String html = AssetUtil.readAssetsFile(

context, filename); webView.loadDataWithBaseURL(

"file://", html, "text/html","utf-8", null);

Native side

function onClick() {

Android. jsOnNextArticle(this.id); }

JavaScript side

public void showArticle(long id, String content) { webView.loadUrl("javascript: jsShowArticle(" + id

+ ", \" + Uri.encode(content) + "\");") } .. public void jsOnNextArticle(long articleId) {

… }

“API” glue

public void showArticle(long id, String content) { webView.loadUrl("javascript: jsShowArticle(" + id

+ ", \" + Uri.encode(content) + "\");") } .. public void jsOnNextArticle(long articleId) {

… }

“API” glue

Summary (Hybrid apps)

• Content centered apps

•  FAQ, User License, …

•  1-1.5x more effort than native

• Pays of when targeting >= 3 platforms

Read ON -  The real problem with Android fragmentation

-  Where does Android fragmentation hide?

-  The technical adventure building a hybrid app.

-  Fast track to Android design.

Interested in Android? @MaksimGolivkin

Care to give feedback? maksim@golivkin.eu