UI onClick callback via Layout.xml file

In my develop habit, I usually use the 'OnClickListener' to listen the button click.
In this topic, I will show you how to listen the button with xml layout file.

The sample code is following:

In MainActivity.java:

package com.example.onclicktest;

import com.example.onclicktest.R;
import android.app.Activity;
import android.widget.Toast;

public class MainActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  this.setContentView(R.layout.activity_main);
 }
 /**Called when button clicked*/
 public void onClick(View view){
  if(view.getId() == R.id.btn_test_click){
   Toast.makeText(this, "Button Clicked.", Toast.LENGTH_SHORT).show();
  }//if(view.getId() == R.id.btn_write_test_file)
 }
}

In avtivity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    
    <Button
        android:id="@+id/btn_test_click"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_centerVertical="true"
        android:text="TestBotton"
        android:onClick="onClick" />

</RelativeLayout>

The callback function has two condition:
1. the method must be 'public'.
2. the parameter of the method must only be 'View'.