Android Introduction

1
Android Introduction

• Hello World

2
Tutorial

• http//developer.android.com/resources/tutorials/h
  ello-world.html
• http//mobiforge.com/developing/story/getting-star
  ted-with-android-development?dm_switchertrue

3
Create a New Android Project

• From Eclipse, select File gt New gt Android
  Project.
• Fill in the project details with the following
  values
• Project name HelloAndroid
• Application name Hello, Android
• Package name com.example.helloandroid (or your
  own private namespace)
• Create Activity HelloAndroid
• Click Finish

4
Create a New Android Project
5
Create a New Android Project

• Project name - the name of the project
• Package name - the name of the package. This name
  will be used as the package name in your Java
  files. Package name must be fully qualified. The
  convention is to use your company's domain name
  in reverse order
• Activity name - the name of the activity in your
  Android application. In Android, think of an
  activity as a screen containing some actions,
  hence the name "activity"
• Application name - the user-friendly name of the
  application that will be displayed in the
  Applications tab of the Android UI

6
Package Content
Java code for our activity
All source code here
Generated Java code Helps link resources to Java
code
All non-code resources
Layout of the activity
Images
Strings used in the program
Android Manifest
7
the various fields when create a new Android
project

• First, the src folder contains your Java source
  files. The HelloAndroid.java file is the source
  file for the HelloAndroid activity you specified
  when you created the project earlier.
• The R.java file is a special file generated by
  the ADT to keep track of all the names of views,
  constants, etc, used in your Android project. You
  should not modify the content of this file as its
  content is generated automatically by the ADT.
• The Android Library contains a file named
  android.jar. This file contains all the classes
  that you would use to program an Android
  application.
• The res folder contains all the resources used by
  your Android application. For example, the
  drawable folder contains a png image file that is
  used as the icon for your application. The layout
  folder contains an XML file used to represent the
  user interface of your Android application. The
  values folder contains an XML file used to store
  a list of string constants.
• The AndroidManifest.xml file is an application
  configuration file that contains detailed
  information about your application, such as the
  number of activities you have in your
  application, the types of permissions your
  application needs, the version information of
  your application, and so on.

8
HelloAndroid.java

• Open the HelloAndroid.java file, located inside
  HelloAndroid gt src gt com.example.helloandroid)
• package com.example.helloandroid
• import android.app.Activity
• import android.os.Bundle
• public class HelloAndroid extends Activity
• / Called when the activity is first
  created. /
• _at_Override
• public void onCreate(Bundle
  savedInstanceState)
• super.onCreate(savedInstanceState)
• setContentView(R.layout.main)

9
HelloAndroid.java

• The basic unit of an Android application is an
  Activity.
• An Activity displays the user interface of your
  application, which may contain widgets like
  buttons, labels, text boxes, etc
• When the activity is loaded, the onCreate() event
  handler is called.
• The activity loads its UI from the XML file named
  main.xml. This is represented by the constant
  named R.layout.main (generated automatically by
  the Eclipse as you save your project).
• If you examine the main.xml file located in the
  res/layout folder

10
Run the Application

• The Eclipse plugin makes it easy to run your
  applications
• Select Run gt Run.
• Select "Android Application".

11
/res/layout/main.xml

• lt?xml version"1.0" encoding"utf-8"?gt
• ltLinearLayout xmlnsandroid"http//schemas.androi
  d.com/apk/res/android"
• androidorientation"vertical"
• androidlayout_width"fill_parent"
• androidlayout_height"fill_parent"
• gt
• ltTextView
• androidlayout_width"fill_parent"
• androidlayout_height"wrap_content"
• androidtext"_at_string/hello"
• /gt
• lt/LinearLayoutgt

12
XML attributes

• xmlnsandroid
• This is an XML namespace declaration that tells
  the Android tools that you are going to refer to
  common attributes defined in the Android
  namespace. The outermost tag in every Android
  layout file must have this attribute.
• androidid
• This attribute assigns a unique identifier to
  the TextView element. You can use the assigned ID
  to reference this View from your source code or
  from other XML resource declarations.
• androidlayout_width
• This attribute defines how much of the available
  width on the screen this View should consume. In
  this case, it's the only View so you want it to
  take up the entire screen, which is what a value
  of "fill_parent" means.

13
XML attributes

• androidlayout_height
• This is just like androidlayout_width, except
  that it refers to available screen height.
• androidtext
• This sets the text that the TextView should
  display. In this example, you use a string
  resource instead of a hard-coded string value.
  The hello string is defined in the
  res/values/strings.xml file. This is the
  recommended practice for inserting strings to
  your application, because it makes the
  localization of your application to other
  languages graceful, without need to hard-code
  changes to the layout file.

14
/res/values/strings.xml

• In Android, the UI of each activity is
  represented using various objects known as Views.
  You can create a view using code, or more simply
  through the use of an XML file.
• In this case, the UI Is represented using an XML
  file.
• The ltTextViewgt element represents a text label on
  the screen while the ltLinearLayoutgt element
  specifies how views should be arranged.
• Notice that the ltTextViewgt element has an
  attribute named androidtext with its value set
  to "_at_string/hello".
• The _at_string/hello refers to the string named
  hello defined in the strings.xml file in the
  res/values folder.
• lt?xml version"1.0" encoding"utf-8"?gt
• ltresourcesgt
• ltstring name"hello"gtHello World,
  HelloAndroid!lt/stringgt
• ltstring name"app_name"gtHelloAndroidlt/stringgt
• lt/resourcesgt

15
Modify strings.xml

• lt?xml version"1.0" encoding"utf-8"?gt
• ltresourcesgt
• ltstring name"hello"gtHello, Android! I am a
  string resource!lt/stringgt
• ltstring name"app_name"gtHello,
  Androidlt/stringgt
• lt/resourcesgt

16
Run it !
17
Modify the main.xml

• Let's now modify the main.xml file. Add the
  following ltButtongt element
• lt?xml version"1.0" encoding"utf-8"?gt
• ltLinearLayout xmlnsandroid"http//schemas.androi
  d.com/apk/res/android"
• androidorientation"vertical"
• androidlayout_width"fill_parent"
• androidlayout_height"fill_parent"
• gt
• ltTextView
• androidlayout_width"fill_parent"
• androidlayout_height"wrap_content"
• androidtext"_at_string/hello"
• /gt
• ltButton
• androidid"_at_id/btnClickMe"
• androidlayout_width"fill_parent"
• androidlayout_height"wrap_content"
• androidtext"Click Me!"
• /gt

18
Run it !
19
Construct UI

• package com.example.helloandroid
• import android.app.Activity
• import android.os.Bundle
• import android.widget.TextView
• public class HelloAndroid extends Activity
• / Called when the activity is first created.
  /
• _at_Override
• public void onCreate(Bundle savedInstanceState)
  
• super.onCreate(savedInstanceState)
• TextView tv new TextView(this)
• tv.setText("Hello, Android")
• setContentView(tv)

20
Run it
21
R class

• In Eclipse, open the file named R.java (in the
  gen/ Generated Java Files folder).
• The R.java file is a special file generated by
  the ADT to keep track of all the names of views,
  constants, etc, used in your Android project. You
  should not modify the content of this file as its
  content is generated automatically by the ADT
• package com.example.helloandroid
• public final class R
• public static final class attr
• public static final class drawable
• public static final int icon0x7f020000
• public static final class id
• public static final int
  textview0x7f050000
• public static final class layout
• public static final int main0x7f030000
• public static final class string
• public static final int
  app_name0x7f040001

22
AndroidManifest.xml

• The AndroidManifest.xml file is an application
  configuration file that contains detailed
  information about your application, such as the
  number of activities you have in your
  application, the types of permissions your
  application needs, the version information of
  your application, and so on.
• lt?xml version"1.0" encoding"utf-8"?gt
• ltmanifest xmlnsandroid"http//schemas.android.co
  m/apk/res/android"
• package"com.example.helloandroid"
• androidversionCode"1"
• androidversionName"1.0"gt
• ltapplication androidicon"_at_drawable/icon"
  androidlabel"_at_string/app_name"gt
• ltactivity androidname".HelloAndroid"
• androidlabel"_at_string/app_name"
  gt
• ltintent-filtergt
• ltaction androidname"android.inte
  nt.action.MAIN" /gt
• ltcategory androidname"android.in
  tent.category.LAUNCHER" /gt
• lt/intent-filtergt
• lt/activitygt
• lt/applicationgt
• lt/manifestgt