CSCU9YH: Lecture 1

CSCU9YH

Development with Android

Computing Science and Mathematics

University of Stirling

CSCU9YH: Lecture 1 1

Android Context

3

CSCU9YH: Lecture 1

Smartphone Market share

Source: http://www.idc.com/promo/smartphone-market-share/os4

Smartphone Penetration by Country

5

CSCU9YH: Lecture 1

Pros and Cons of Android

Good:

• Open source (Apache

licence)

• Familiar developer

languages

• Developer/distribution

friendly

• Carrier independence

• Open Handset Alliance

Not so Good:

• Version

incompatibilities

• Inconsistent

experiences

• Only Java-like syntax,

not identical APIs

6

Android Information• Many textbooks, e.g.:

– ‘Hello, Android’, E. Burnette

– ‘Professional Android Application Development’, R. Meier

• Good online sources, e.g.:

– http://www.android.com

– http://developer.android.com

• Versions named after sweet things, e.g.:

– Froyo (2.2), Gingerbread (2.3)

– Honeycomb (3.0)

– Ice Cream Sandwich (4.0)

– Jelly Bean (4.1 -4.3), Kitkat (4.4)

– Lollipop (5.0) Data collected during a 7-day period ending on 4th January 2016.

http://developer.android.com/about/dashboards/index.html7

CSCU9YH: Lecture 1

…. A more recent update

8

Data collected during a 7-day period ending on 9th January 2017.

Source: http://developer.android.com/about/dashboards/index.html

… just for reference …Version Codename API Distribution

2.3.3 -

2.3.7Gingerbread 10 1.0%

4.0.3 -

4.0.4Ice Cream Sandwich 15 1.1%

4.1.x

Jelly Bean

16 4.0%

4.2.x 17 5.9%

4.3 18 1.7%

4.4 KitKat 19 22.6%

5.0Lollipop

21 10.1%

5.1 22 23.3%

6.0 Marshmallow 23 29.6%

7.0 Nougat 24 0.5%

http://developer.android.com/about/dashboards/index.html Accessed 13th Jan 20179

CSCU9YH: Lecture 1

Android Architecture

http://developer.android.com/about/versions/index.htm

Or ART

10

Dalvik Virtual Machine

• Register-based (most VMs are stack-based):

– Java is stack-based, Android is register-based

• Optimised for low memory environments:

– trimmed to occupy and use less space

– no Just In Time compiler until version 2.2

– has its own bytecode, i.e. Dalvik is not a Java VM

– aims to be efficient on small devices

– Infinite registers, fewer instructions (30%), smaller code

11

CSCU9YH: Lecture 1

ART Virtual Machine

• Android Runtime

• Successor to Dalvik

• JIT vs AOT compilation

• At installation time compiles dex files using an on device

compiler

• Main improvements

– Ahead-of-time (AOT) compilation

– Improved garbage collection

– Development and debugging improvements

12

Application Architecture• Each app (application) runs in its own process:

– each process has its own VM, hence the optimisations

• Libraries are written in C/C++:

– exposed to apps via wrappers

• Application components:

– Activities

– Services

– Broadcast Receivers

– Content Providers

– Intents

– Resources

http://markfaction.wordpress.com/2012/07/15

/stack-based-vs-register-based-virtual-

machine-architecture-and-the-dalvik-vm/ 13

CSCU9YH: Lecture 1

Application Architecture

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Activities

• Each visual interface is an activity:

– one application may have many

activities

– each is a subclass of the Activity class

– generally there is a starting activity

– one activity may start/launch

another activity

15

CSCU9YH: Lecture 1

States of An Activity

• Active/running:

– a foreground activity is the focus of input

– top of the activity stack

• Paused (killable):

– activity has lost focus but is still available to the user

– still alive, retains all state, tied to window manager

• Stopped (killable):

– when completely obscured

from the user

– retains state unless killed

16

Activities and Views

• Activities have a default drawing area:

– typically fills the screen, but may not

– additional windows permitted, also pop-ups (‘toasts’)

and dialogue boxes

– May subdivide screen into fragments (since Android 3);

helps different screen sizes but is not covered here

– visual spaces constructing using Views

• Views are visual building blocks like widgets:

– buttons, text fields, scroll bars, etc.

– placed in a window with the Activity.setContentView

method17

CSCU9YH: Lecture 1

Services

• Extend the Service base class

• No visual representation

• Services run in the background:

– for an indefinite amount of time

– generally in their own threads (within processes)

• Typical examples:

– music playback

– background download

18

Broadcast Receivers

• Extend the BroadcastReceiver class

• A single function receives and reacts to broadcast

announcements, e.g.:

– time zone change

– low battery

– an incoming message

• No user interface, but may launch an activity or

notification:

– notifications may be via vibration, chime, etc.

• Broadcasts may be initiated by apps: sendBroadcast()

19

CSCU9YH: Lecture 1

Content Providers

• Make app data available to others

• Flexible storage through a relational database

(SQLite)

• The Contacts app is a good database example:

– but beyond the scope of this module

20

Intents and Intent Filters

• An Intent is a message like an event passed

among components:

– one component that wants to invoke another simply

expresses its intent to have a job performed

• A component claims that it can do such a job

through an IntentFilter

• An Intent is handled by Android to perform a job

• A PendingIntent is an intent delegated to another

app, typically in response to a future event

21

CSCU9YH: Lecture 1

Uniqueness of Intent Model

• Intents resemble parameter passing in APIs

• Consider the differences:

– API calls are synchronous but intent-based invocation

is asynchronous (mostly)

– API calls are bound at compile time but intent-based

calls are bound at run time (mostly)

• Intents are thus more like events:

– components do not need to be aware of each other

22

Resources• Apps can have many kinds of resources such as:

– values (strings, numbers, colours, …)

– styles and themes

– drawables (images)

– views

– layouts

• Resources are stored in the app res folder

• Resources can be varied according to the context:

– different languages (values-en, values-fr, …)

– different screen sizes (layout-small, layout-medium, …)

– different screen dots/inch (layout-ldpi, layout-mdpi, …)23

CSCU9YH: Lecture 1

Defining and Using Resources

• Resources can be defined using XML, but are

better defined directly in an IDE (e.g. Android Studio)

• Resources are accessed in code using the R class

(created in the app gen folder):

– this is automatically generated by the IDE

– it names integer constants to identify resources

setContentView(R.layout.main);

Button go = (Button) findViewById(R.id.go);

Resources resources = getResources();

String name = resources.getString(R.string.appName);

Drawable icon = resources.getDrawable(R.drawable.appIcon);24

Hello Androidpackage uk.ac.stir.cs.android.Hello;

import android.app.Activity;

import android.os.Bundle;

import android.widget.TextView;

public class HelloActivity extends Activity {

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

TextView textView = new TextView(this);

textView.setText("Hello Android");

setContentView(textView);

}

}

http://www.mkyong.com/android/android-hello-world-example/25