android:onClick - define callback method when a View clicked, in XML layout.

A callback method can be defined in XML layout file, using "android:onClick". It define the name of the method in this View's context to invoke when the view is clicked. This name must correspond to a public method that takes exactly one parameter of type View.

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    >

<TextView  

    android:layout_width="fill_parent" 

    android:layout_height="wrap_content" 

    android:text="@string/hello"

    />

<Button  

    android:layout_width="fill_parent" 

    android:layout_height="wrap_content" 

    android:text="Button 1"

    android:onClick="onClick"

    />

<Button  

    android:layout_width="fill_parent" 

    android:layout_height="wrap_content" 

    android:text="Button 2"

    android:onClick="onClick"

    />

<Button  

    android:layout_width="fill_parent" 

    android:layout_height="wrap_content" 

    android:text="Button 3"

    android:onClick="onClick"

    />

</LinearLayout>

package com.exercise.AndroidOnClick;



import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.Toast;



public class AndroidOnClickActivity extends Activity {

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

    }

    

    public void onClick(View view){

    	Toast.makeText(AndroidOnClickActivity.this, 

    			"onClick:\n" + view.toString(), 

    			Toast.LENGTH_LONG).show();

    }

}