1 mobile computing java, android, and eclipse copyright 2015 by janson industries

1

Mobile Computing

Java, Android, and Eclipse

Copyright 2015 by Janson Industries

Copyright 2015 by Janson Industries2

Objectives▀ Explain

Application organization in Eclipse

Basic Java concepts

How to code and run an Android app in the emulator

Controlling the emulator

The Android app life cycle


Eclipse▀ Has a variety of perspectives

Java, Debug, DDMS

▀ Each perspective consists of a unique set of functions and views of the application resources Java shows source code and allows the

programmer to edit it

Debug shows the stack trace (logic flow) of a running app

DDMS allows access to the device/emulator’s file system


Perspective indicated in upper right hand corner

Java Perspective window initially consists of 6 panes – only need 4. Can close Task List and Connect Mylyn

Resize panes by clicking and dragging bordersDouble click view tab to expand view and fill perspective

window

Panes contain viewsViews indicated by tabs at top of pane, switch view by

clicking tab


Can have multiple perspectives open but only one is active


Open a new perspective by clicking Window, Open Perspective, then choose a perspective

Switch between perspectives by clicking perspective button


Eclipse▀ All of an application’s

resources are stored in a project Source code

Images

XML

▀ The resources can be further organized into folders and packages


Project

Package Folder Package Folder File

Eclipse

▀ Packages and folders hold the majority of an application’s resources Source code Images XML

▀ Java source code must go into a package


Android Java

▀ An Android application’s programs are called activities

▀ Files with an extension of .java hold an activity’s source code

▀ To create an activity you have to have a project and a package to put it in


Creating an Application▀ Click File, New and then Project

▀ Select Android Project

▀ Specify:

Project, package, activity and application names

A build target


Click File, New, and Project then expand Android, select Android Application Project and click Next


Give names to the Application (Howdy), Project (MyFirstProject) , Package (my.first.pkg), specify 2.1, click

Next


Click Next

Creating an Application


Can create a unique icon

We’ll accept default and click Next



Will create a Hello World activity for us

Click Next



Change activity name to HowdyActivity

Click Finish



Creating an Application Eclipse will create the

Project Packages and folders Files

It even creates a working application In a file called HowdyActivity.java File stored in a package called

my.first.pkg in source folder src


To Run an Application In Package Explorer, expand

MyFirstProject, src, & my.first.pkg

Right click HowdyActivity and select Run As then Run Configurations

Select Android Application and click the New button


Give the configuration a name and specify the ProjectClick Apply and Run


To Run an Application First time will take a while

Emulator must configure itself and will launch

The emulator is displayed

You have to click and drag the lock icon to see the results of the activity


Click and drag the lock icon to the right


If app doesn’t start, rerun in Eclipse


Console should show that app was installed just not run


Voila!


To Run an Application Once emulator is running, results will

be shown must faster

To close emulator:

Right click Android button in the System Tray

Select Close Window

Or click the Close Window button

Can control the size of the emulator


Control Emulator Size Run emulator before running an

activity. Click: Window (in the command bar)

AVD Manager

Select the AVD

Click Start

Click Scale display to real size

Specify screen size

Click Launch


1

2

3

4

5


New size fits on the screen better

Need to go back and close AVD Manager window


How Does It Work The generated application is

pretty complicated and requires a lot of Java knowledge

Let’s first learn some Java (then some XML) and then generate our own application

Later we will cover the workings of the generated application


Java Java programs are called classes

Classes are stored in files that have an extension of .java

Classes are comprised of a header and a body


Java Class Class header defines:

The source code as a class (e.g. “class” keyword is used)

Access allowed (e.g. “public”)

The name of class Must begin with an upper case letter Is case sensitive Cannot contain spaces Must match .java file name prefix

• I.e. a class named Customer must be in a file named Customer.java


Java Class The class body is enclosed in braces

{} and comprised of class/global variables and methods

Simple class example: public class ClassName {

global variable definition

global variable definition

method{}

method{}

}


Java Method Comprised of a header and body

Header definition comprised of: Modifiers (e.g. “private”, “public”,

“static”) Return value (e.g. “void”, “String”) Method name

Begins with a lower case letter (e.g. getMailingLabel, main)

Parameter(s)/received value(s) in parenthesis (e.g. (String name), (int age), () means no params)


Java Method Header Method header/definition examples:

public void setName(String custName)

public String getMailingLabel()

public static void main(String[ ] args) A static method can be run all by itself’

• It is self sufficient/stand alone

If multiple values passed/received simply separate by commas

(String itemName, int itemPrice)


Java Method Header Private methods:

Can only be accessed/run by other methods within the class

Public methods: Can be accessed by objects

external to the class

Are considered the class “interface” This is how other classes/objects can

interface with this class


Java Method Body Enclosed in braces { }

Comprised of:

Local variable definitions

Executable statements

Variable definition comprised of:

The variable type

The variable name

A semicolon (;)


Java Method Body Variable definition examples

int age;

String customerName;

double salary;

String street, city, state, zip;

In addition, variable definitions can

Specify access modifiers

Initialize the variable


Java Method Body Variable definition examples

private int age = 22;

String customerName = new String( “Joe”) ;

double salary = 1123.54;

public String street, city, state, zip;

Executable statements also must end in semicolons

System.out.println(“Howdy”);


Java Method Body Example

public void onCreate(Bundle aBundle) {

super.onCreate(aBundle);

String greeting = new String(“******Hello*******”);

System.out.println(“A print of static text");

System.out.println(“The value of greeting is: ” + greeting);

}

statementsvariabledefinitio

n


Classes If a class is stored in a package,

the class must have a package statement at the very beginning of the source code

So for example, the HowdyActivity class has the following:

package my.first.pkg;


Activity Classes Activity classes are executable

Some special requirements The class must be defined as an

acitivty When first run, the activity’s

onCreate method will be executed onCreate must

accept a Bundle objectcall it’s superclass’ onCreate

method and pass the bundle


Superclass All classes are related in a

hierarchy

This parent/child relationship is called a superclass/subclass relationship for java classes

Just like in real life the child/subclass inherits all the parent/superclass’ variables and methods


Superclass For example, an EditText class is

a visual component that a user can enter text into

This is it’s lineage:

Object

View

TextView

EditText


Import Statements All the java classes in the SDK are

stored in packages

To use these classes you can specify the location (i.e. the package(s) that hold them android.app.Activity

android.os.Bundle

This is called a fully qualified file reference


Import Statements Fully qualified file references

mean extra typing and more errors

If import statements are added we can use non-fully qualified file references for the classes (Activity, Bundle )

import android.app.Activity;

import android.os.Bundle;


Import Statements The import statements come after

the package statement but before the class header

Now if we want to use the Bundle class we can type Bundle

Instead of android.os.Bundle


Import Statements So you can use fully qualified file

references like this :

Or use import statements and non-fully qualified file references like this :

public void onCreate(Bundle aBundle) {

public void onCreate(android.os.Bundle aBundle) {


Activity Classes To define the class as an activity (I.e. a subclass of the

Activity class) an extends clause must be included in the class header as follows:

Comments (non-executable statements) preceded by //

public class HowdyActivity extends Activity {


Putting It All Togetherpackage my.first.pkg; //Identifies the package the class is in

import android.app.Activity; //Identifies the location of classes import android.os.Bundle; //this class will be using

public class HowdyActivity extends Activity { //Class header

//Method header public void onCreate(Bundle savedInstanceState) { //Superclass’ onCreate method invoked super.onCreate(savedInstanceState); //String variable defined and initialized String greeting = new String("******Hello*******"); //Two lines of text are displayed System.out.println("A print of static text"); System.out.println("The value of greeting is: " + greeting); }}


Putting It All Together So in HowdyActivity:

Comment out the one setContentView statement Precede the statement with // Keystroke short cut:

• Select the statement• Click Ctrl+/

After the commented out statement, add the three statements from the previous slide that

Create the String variable Display the two lines of text


Putting It All Together Code should look like this


Running the New App In the Package Explorer view, select the MyFirstProject

Click the Run button (green circle with white arrow head) You’ll be prompted to save the changes

Click Yes

Nothing happened!?! This gives us the opportunity to introduce LogCat


LogCat LogCat holds all the system generated msgs and any println statements run in

the code

If LogCat not displayed at bottom of window, display by clicking: Window Show View Other Android (to expand it) LogCat OK


LogCat If your LogCat has no msgs (as

below) it is because the emulator doesn’t have “focus”


Switch to DDMS perspective (Window, Open Perspective) and click on the emulator in

the Devices view


If nothing appears, click the down arrow and select Reset adb

Emulator will be redisplayed


Go back to the Java perspective and scroll to the right in LogCat to display all the text

Common mistake: looking at the console not LogCat


If app rerun, info will not be redisplayed because app is already created

Prove by clearing LogCat and rerunning


New system msgs will be there but not the text from the app

This brings up the Android application life cycle!


Application Life Cycle▀ There are 4 states that an application

can be in Active: the activity can be used by the user

Paused: The activity is partially obscured (a new non-full screen or transparent activity is active)

Stopped: The activity is totally obscured (a new full screen activity is active)

Finished: the activity has been closed.


Application Life Cycle▀ Based on changes in the application’s

“state”, several other methods will be called : protected void onStart(){}

protected void onRestart(){}

protected void onResume(){}

protected void onPause(){}

protected void onStop(){}

protected void onDestroy(){}


Application Life Cycle▀ An application’s “state” can be

changed by user actions like:

Starting a new application

Closing an application

▀ What the new state will be will vary by what is being run Does new app take up the whole

screen?

Is there enough MM for new app?


Application Life Cycle▀ For example, when an app is

first run it means the following methods will be run:

onCreate()

onStart()

onResume()

▀ Let’s prove it!


Application Life Cycle▀ We’ll add the following two new

methods:

▀ And change onCreate a little

protected void onStart(){super.onStart();System.out.println("*****onStart was run");

}

protected void onResume(){super.onStart();System.out.println("*****onResume was run");

}


Here’s all the new code


Application Life Cycle▀ Need a new emulator with the

buttons enabled

▀ Need to clone a definition Only user defined emulators can

be edited

▀ Start the AVD manager


Click Device Definitions tab then Double click Galaxy

Nexus definition

Edit definition, click Clone

Device


▀ Define new AVD

▀ Select the first Galaxy Nexus listed

▀ If correct one selected, RAM will be 512

▀ Fill in rest of info


Select and Start the new emulator


Run app and LogCat shows the msgs


In emulator, click home button to stop the app

Run the app again


Scroll up and notice onCreate was not run, that’s because app was already created but

stopped


The Whole Thing

Active

ActivityStarted

onStart

onResume

onCreate

onPause

Paused Stoppedon

Stop

onRestart

Finished

onDestroy

Whoa! Maybe we should go step by

step


In the Beginning

76

Active

ActivityStarted

onStart

onResume

onCreate

▀ When the application is first run…


From an Active State

77

▀ The application can go to any of the other three states…

Activeon

Pause Paused

onStopActive

onPause Finishe

d

onDestroy

Activeon

Pause Stoppedon

Stop


From an Paused State

78

▀ The application can go Active or Stopped states…

Paused

Stopped

Active

onResume

onStop


From an Stopped State

79

▀ The application can go to Finished or Active states…

Activeon

Restart

Finished

onDestroy

Stopped

onStart

onResume


Android App Life Cycle▀ Why all the different methods?

▀ You might want the app to do different functions when the state is changed When closed, free up resources

When restarted, refresh info on screen

When paused, stop playing music


Emulator Glitches▀ When emulator run, message that says

something like:

Image is used by another emulator

▀ Need to go out and delete these two files in the emulator definition

▀ Substituting for username and emulator name

C:/Users/username/.android/avd/EmulatorName/cache.img

C:/Users/username/.android/avd/EmulatorName/userdata-qemu.img


Emulator Glitches▀ If it starts running slowly or if logcat isn’t

working well

Not displaying msgs quickly

Not allowing msg deletions

▀ Restart Eclipse

▀ Gives Eclipse a chance to clean up internally


Emulator Glitches▀ If you get this msg:

ADB server didn't ACK, failed to start daemon

▀ Start Task Manager and kill the adb.exe process

▀ Close and restart Eclipse


Points to Remember▀ Java classes stored in a project's

package

▀ Java class consists of global level variables and methods

▀ Java method consists of local level variables and executable statements

▀ Activity classes are executable


Points to Remember▀ LogCat displays system and

program msgs

▀ An app can be in four states Active

Paused

Stopped

Finished

▀ Changes in state will result in different methods being executed

1 mobile computing java, android, and eclipse copyright 2015 by janson industries

Documents

janson industriescopyright

android application

new perspective

open perspective

android projectspecify

ddmseach perspective

perspective windowpanes

perspective button copyright