Google Android Tutorial

From the toolbox, we learn that we are having controls like button,check,radio,spinner,edittext(textbox) and  textview (label) etc. There is also a combo  to choose  layout, in the canvas screen.  I am choosing 'absolute layout'. I simply drag and drop a button and an editview on the canvas.(Drag and drop, do not click and drop! It won't work).

You will notice a number of tabs in toolbox. Select 'properties' tab.. After clicking the button on the canvas, give the id property of button as @id/button1. Similarly, for editview as @id/text1. Also, button2 and text2 After this, just click the 'generate' button at the bottom of  the blank window. We get the following XML file(main.xml) automatically generated.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:layout_width="fill_parent" android:layout_height="wrap_content"
	android:padding="10px">
	<EditText android:id="@+id/text1" android:layout_width="fill_parent"
		android:layout_height="wrap_content" />
	<Button android:id="@+id/button1" android:layout_width="wrap_content"
		android:layout_height="wrap_content" android:layout_below="@id/text1"
		android:layout_alignParentRight="true" android:layout_marginLeft="10px"
		android:text="click" />
	<EditText android:id="@+id/text2" android:layout_width="fill_parent"
		android:layout_height="wrap_content" android:layout_below="@id/button1" />
	<Button android:id="@+id/button2" android:layout_width="wrap_content"
		android:layout_height="wrap_content" android:layout_below="@id/text2"
		android:layout_alignParentRight="true" android:layout_marginLeft="10px"
		android:text="click" />
</RelativeLayout>

We can now create our java source file. The code refers to main.xml for id of the controls.
(d:\android\mydemos\ex1\demo.java).This is our work folder.

package mypack.mydemos;


import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.*;


public class demo extends Activity  
{

Button     button1,button2;
EditText   text1,text2;

    @Override

    public void onCreate(Bundle icicle)
    {
       	super.onCreate(icicle);
       	setContentView(R.layout.main);
	text1=  (EditText) findViewById(R.id.text1);
	button1 = (Button) findViewById(R.id.button1);

	text2=  (EditText) findViewById(R.id.text2);
	button2 = (Button) findViewById(R.id.button2);
	button1.setOnClickListener(new clicker());
 	button2.setOnClickListener(new clicker());
   }

 //-----------------------------------

 class  clicker implements Button.OnClickListener
  {               
  public void onClick(View v)
     {
     if(v==button1){text1.setText("welcome"); }
     if(v==button2){text2.setText("hello");   }     
     }

  }

}

The Android documentation and sample programs use anonymous inner class. I think it is quite unnecessary and is very tedious to follow. Instead, I have used user-defined 'clicker'. This makes the code cleaner and more readable. This is just like any Swing program. In Android Terminology, an Activity is like a frame in swing (a screen). Just like ActionListener, here also we have, OnClickListener. I am not going into detailed theory now. I just  want to show how to develop and run a program first. Theory will follow later.

We have to copy this file(demo.java) to D:\android\tools\demo\src\mypack\mydemos

Go to d:\android\tools\demo

Give path= c:\winNT\system32;c:\jdk1.5\bin;e:\ant1.6\bin

(carefully note that this will not work with jdk1.4.2. It requires jdk1.5).

Secondly, how about the reference to Ant? Ant is a famous build tool from Apache Software foundation. Android requires the latest version of Ant for Windows(ie) Ant1.6. Do I have to know how to write the Ant's build.xml file? NO. It is automatically created by the command.

So, I downloaded ant1.6 from the Apache website. It is a compact zip file. I have unzipped it and placed it as E:\ant1.6). Now use the command 'ant'

d:\android\tools\demo>ant

We will get a series of messages. If we had done the previous steps correctly, we will get the message 'BUILD SUCCESSFUL".  Otherwise, we will get error messages, with line numbers where the errors occurred. We can correct them and build again.

The build process would have created a zip file named 'demo.apk' in demo\bin folder. All that remains now is to run the program in the emulator. As you remember, we have already started the emulator and it is running.

Now copy d:\android\tools\demo\bin\demo.apk  to d:\android\tools. After copying, give the command as:

...\tools>adb   install    demo.apk

After giving this command. go to the emulator window. You will find a checkpattern displayed for a while. Then an additional button appears in the screen with caption 'demo'. Our program has been installed. We can test it by clicking on this 'demo'button.

You can execute the program 'demo' now. Two textboxes and two buttons will appear. Click on button1. 'welcome' will appear in text1. Click on button2.'how are you?' will appear in text2. The result is shown  below.

That completes our first  demo in  android.