INTRODUCTION TO ANDROID

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Application Components An Android application is made of up

one or more of the following components Activities

We will only discuss activities in this chapter

Services Broadcast Receivers Content Providers

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Application Components (Activities) (1) An Activity has a single screen with a

UI Program logic is wired to a screen in a

structured way (MVC) A program is initiated by running the default

activity An activity is executed via predefined

callbacks These are just procedures called by the

Android infrastructure Most programs will have several

activities

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Application Components (Activities) (2) An activity is a class that drives from

Activity

Then we must override a couple of base class methods onCreate() And several others

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Application Components (Activities) (onCreate) @Override indicates that we are

overriding a base class method It’s an informative annotation Annotations are used to control compiler

behavior Similar to .NET attributes

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Application Components (Activities) (onCreate) super.onCreate calls the base class

method Super is roughly equivalent MyBase in VB It typically appears as the first statement

in the method

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Application Components (Activities) (onCreate) setContentView takes one argument – the

resource id corresponding to the activity It associates a particular view with the

activity The resource is always named R Layout is the layout that you want to use Followed by the resource id of the layout

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Application Components (Layout) (1) A layout describes the visual structure

for a UI, such as the UI for an activity It’s an XML document, so you need

some familiarity with XML Android provides an XML vocabulary

that corresponds to the View classes and subclasses, such as those for widgets and layouts

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Application Components (Layout) There are different types of layouts for a

screen LinearLayout RelativeLayout Lists and Grids Web

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Application Components (LinearLayout) LinearLayout aligns child objects

vertically or horizontally Use the android:orientation attribute to

specify the layout direction (vertical / horizontal)

Scrollbars appear if the window length exceeds the screen length

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Application Components (RelativeLayout) RelativeLayout aligns objects relative

to an each other (siblings) Such as:

Child A to the left of child B Or align to the parent

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Application Components(Buttons and Events) Like a VB button

Text or an icon can appear in the visible region

They respond to click events (although the syntax differs)

http://developer.android.com/guide/topics/ui/controls/button.html

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Application Components (Declaring a Button) A button has a width and height The button’s text appears in strings.xml

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Application Components (Handling a Click – Method 1) When the user clicks a button, the

object receives an onClick event which you can handle

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Application Components (Handling a Click – Method 2) The event handler can also be declared

programmatically using an anonymous class The book uses this technique

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Application Components (Toast) A toast is a form of Android popup

The size of the popup is just large enough to render the message

If you want the user to respond, use a Notification instead of a toast

To create, use the makeText method of the Toast class

http://developer.android.com/guide/topics/ui/notifiers/toasts.html

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Application Components (Toast Example)

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Introduction to Input Controls Button operates like a VB button TextView operates like a VB TextBox CheckBox operates like a VB check box Etc.. All are configured as XML

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Strings.xml Strings literals are stored in the file

strings.xml

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Strings.xml And we reference those strings from the layout.xml

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Resource Files Android R.java is an auto-generated

file by AAPT (Android Asset Packaging Tool) that contains resource IDs for all the resources of res/ directory

If you create any component in the activity_main.xml file, the id for the corresponding component is automatically created in this file The id can be used in the activity source

file to perform any action on the component

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Resource File (Example)

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Creating a First Project Click File, New, Project. Select

Android Application Project

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Define Application Parameters (1) Don’t use an

old MinimumRequired SDK

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Define Application Parameters (1) The Application Name appears in the

store when deployed The Project Name is only relevant to

Eclipse The Package Name contains a reverse

domain name It must be unique and must not be

changed – this is how versioning is performed

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Define Application Parameters (2) Minimum Required SDK contains the

minimum SDK version on which the application will run

Target SDK contains the desired SDK version on which the application will run

Compile with contains the SDK version that will be used to compile the application

Theme defines basic UI characteristics

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Configure Project

Create activity

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Configure Icons Configuring

the icons Just use the

defaults

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Create Blank Activity Create the

default activity This gives you

a blank screen(form)

(Blank Activity)

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Name the Activity and Layout

Choose the default values

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Application Anatomy (1) The file MainActivity.java contains the

java code for the application’s activity (screen) Default methods are created too

(onCreate, …)

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Application Anatomy (2) The purpose of AndroidManifest.xml is

similar to web.config or app.config Simply put, it describes the application

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Application Anatomy (3) The folder values\strings.xml contains

the application’s textual content

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Application Anatomy (4) The file activity_main.xml contains the

XML code that describes the user interface layout

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Setting up the Emulator (1) We can run programs via an emulator or

directly attached to a physical device Using windows, you might need the driver

from the device manufacturer

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Setting up the Emulator (2) Click Window, Android Device

Manager Click Create to create the new device I suggest the following settings

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Setting up the Emulator (3) Under Windows set the memory to no

more than 512MB

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Setting up the Emulator (3)

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Starting the Emulator Set the display

characteristics Note that it takes a while

to start the emulator

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Running Hello World The emulator

should start and be rendered

Again, it takes a while tostart

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Running Hello World (5) Now run the

application

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Guidelines for Running on a Native Host (1) First, plug the device in If running Windows, you will likely need

a device driver

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References http://

developer.android.com/tools/extras/oem-usb.html