Intro to android (gdays)

INTRODUCTIONTOANDROIDDEVELOPMENT

Adejuwon Omolara

Twitter: @_larikraun

Email: [email protected]

Overview

• Android is a software stack for mobile devices that includes an operating system, middleware and key applications.

• Android OS is divided into five sections

• Applications: This is where applications to be installed are written. E.g. Games,

Browser etc.

• Application Framework: This layer provides many higher-level services to

applications in the form of Java classes.

• Android Runtime: This section provides a key component called Dalvik Virtual

Machine. Dalvik VM enables every android application to run in its own process, with

its own instance of the Dalvik VM. Dalvik VM is optimised to run on slow CPU, low

RAM, low power devices. It runs .dex files and not .class nor .jar

• Libraries: e.g. SQLite database, repository for storage and sharing of application.

• Linux Kernel : it provides basic system functionality e.g. process management,

device management etc.

Platform Overview

Android has evolved over the years :

• Android 1.1 *Not relevant in the ecosystem*

• Android 1.5 Cupcake *Not relevant in the ecosystem*

• Android 1.6 Donut *Not relevant in the ecosystem*

• Android 2.0/2.1 Eclair *Not relevant in the ecosystem*

• Android 2.2.x Froyo *Not too relevant in the ecosystem*

• Android 2.3.x Gingerbread *Still somewhat relevant in the ecosystem*

• Android 3. x Honeycomb *Not relevant in the ecosystem*

• Android 4.0.x Ice Cream Sandwich *Still quite relevant in the ecosystem*

• Android 4.1, 4.2, 4.3 Jelly Bean *Very relevant in the ecosystem*

• Android 4.4 KitKat *Very relevant in the ecosystem*

• Android 5.0 Lollipop * Gaining relevance in the ecosystem*

And now we have Lollipop…

Tools you need to get started…

• A fair knowledge of Java

• Latest Java Development Kit (JDK) : Android Apps are

developed using Java.

http://www.oracle.com/technetwork/java/javase/downloads/inde

x.html

• Eclipse Integrated Development Environment (IDE)

https://www.eclipse.org/downloads/ or any other suitable IDE.

• Android SDK

http://developer.android.com

• ADT Tools for Eclipse (via Internet)

http://developer.android.com/sdk/index.html

• Android Virtual Device (AVD) or an android mobile device.

Application Components

Applications use four main components:

• Activity

• Service

• Broadcast Receivers

• Content Providers

Activity

Activities: A single screen that is visible to user. They dictate the UI and

handle the user interaction to the smartphone screen.

public class MainActivity extends Activity {

}

Activity Lifecycle

Services

Services: They handle background processes associated with an

application. They can be used to update an application when it’s not

active.

public class MyService extends Service {

}

Service Lifecycle

Broadcast Receiver

Broadcast Receivers: They handle communication between Android OS

and applications. They listen for android system events.

public class MyReceiver extends BroadcastReceiver {

}

Content Providers

Content Providers: They handle and manage data, usually stored in

database and data access for queries.

public class MyContentProvider extends ContentProvider {

}

More Components…

• Fragments: Represents a behaviour or a portion of user

interface.

• Views: UI elements that are drawn onscreen. They are

responsible for event handling e.g. ContextMenu, Menu etc.

• Widgets: They are more advanced UI elements e.g Button,

CheckBox, ImageView etc.

• Layouts: View hierarchies that control screen format and

appearance of the views.

• Intents: Messages wiring components together. An intent

is composed of an action it needs to perform. They are

used to start activities and to communicate among various

parts of the android system.

• Resources: External elements such as strings, drawables

and constants

• Manifest: Configuration file for the application.

Layout Manager

It is responsible for the layout of itself and its child Views.

Android supports different default layout managers. To get

a desired layout, there are some few terms you would

come across.

android:layout_width defines the width of the widget.

android:layout_heigth defines the height of the widget.

match_parent tells the application to maximize the

widget in its parent.

wrap_content tells the layout to allocate the minimum

amount so that the widget is rendered correctly.

Image source: vogella

Who doesn’t like easy tasks? Well, I do…

Google exposes a number of functionalities in android. To

create spectacular apps, you should make use of them.• Touchscreen

• GPS

• Accelerometer

• Internet

• Audio and Video support

• Contacts

• Security

• Google APIs

API levels

This is an integer value that uniquely identifies the

framework API revision offered by a version of the android

platform.

It lets the android platform describe the maximum

framework API revision that it supports.

It lets applications describe the framework API revision

that they require.

It lets the system negotiate the installation of applications

on the user’s device such that version-incompatible are

not installed.

You can catch more gist on API levels here

Image source: Android’s site

My One-Dollar

To write a working android application, you need to

consider keeping it simple. Nobody likes a complex-for-

nothing application. I encourage drawing mock-ups ( a

visual representation of how you want the application to

look like), flow charts ( a step-by-step approach to

achieving your goal) as one of the first steps before

jumping on your IDE.

You will need to step up your UI/UX game to ‘wow’ your

users.

I think these will help too

• Make Google your friend

• Get familiar with android developers’ site

• Read documentations before using any API

• Join forums that will help. One of the most popular is

stackoverflow

• Get close to the ‘gurus’- they have a lot to offer.

• Read books that will help.

My ‘Hello World’ Application

This is a dummy application that just displays ‘Hello World,

MyFirstApp’

MyFirstApp.java + main.xml =

MyFirstApp.java

The main.xml file

AndroidManifest.xml

package attribute defines the base package for the Java objects referred to in

a particular file.

android:versionCode must be an integer. You typically start from ‘1’ and

increase the value by one if you roll-out a new version of your application.

android:versionName is what the users see. It can be any string.

android:minSdkVersion defines the minimum version of android your

applicaton works on. A user cannot install your application on a device with a

lower API level than specified in this attribute.

android:targetSdkVersion specifies the version on which you tested and

developed. It is a good practice to always set this to the latest Android API

version.

<application> section is a container for declaring android components.

<activity> tag defines an activity component.

android:name="android.intent.action.MAIN" can be started and the category

android:name="android.intent.category.LAUNCHER“ parameter tells the

Android system to add the activity to the launcher.

Questions???