Activity implements various OnClickListeners.

Activity's Inner Class implements View.OnClickListener.

package com.smartcloudcompany.onclickinxml;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class AndroidOnClickDefinitionInXMLActivity extends Activity implements OnClickListener {
    
    private Button buttonWithInnerClassAsListener;
   	
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        buttonWithInnerClassAsListener = (Button) findViewById(R.id.button_with_inner_class_as_listener);
        buttonWithInnerClassAsListener.setOnClickListener(new InnerOnClickButtonListener());
        
    }
	
    /** Inner Class to respond to OnClick events. **/
    class InnerOnClickButtonListener implements OnClickListener {
      public void onClick(View v) {
        Toast.makeText(AndroidOnClickDefinitionInXMLActivity.this, "Button with Inner Class as Listener has been clicked.", 2500).show();
      }
    }
}

main.xml

<?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"
    >
	
	<Button android:id="@+id/button_with_activity_as_listener" 
	android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    
    android:text="Button with Activity As Listener"
    
    android:layout_gravity="center_horizontal"
    android:layout_marginTop="100dp"
	/>
	
	<Button android:id="@+id/button_without_listener" 
	android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    
    android:text="Button Without listener"
    
    android:layout_gravity="center_horizontal"
    
    android:onClick="onButtonClick"
	/>
	
	<Button android:id="@+id/button_with_inner_class_as_listener" 
	android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    
    android:text="Button With Inner Class As Listener"
    
    android:layout_gravity="center_horizontal"
	/>
	
	<Button android:id="@+id/button_with_inline_class_as_listener" 
	android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    
    android:text="Button With Inline Class As Listener"
    
    android:layout_gravity="center_horizontal"
	/>
	
</LinearLayout>