How to Handle OnClick Listener using When keyword in Android?

In this article, we are going to see how can we apply the OnClick event to a button in android with the help of When Keyword,  we can also apply the onClick event to a button in various other ways such as by setOnClickListener and findViewById, by ViewBinding but all these methods are taken a long time to implement and decrease our development speeds, so to overcome these problems we are going to handle OnClick Listener by the Help of When keyword and with the help of View. which makes it super easier and increases our development speed.

When Keyword:  It is very similar to Switch Case in other languages, it executes a block of code when an specified condition is Satisfied .

To implement this first we have to Implement View.OnClickListener in your Activity or Fragment, you have to override the OnClick method on our class.

Step-By-Step Implementation

Step 1: Create a New Project in Android Studio

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. The Code is given in Kotlin language so make sure that you select Kotlin language for your project.

Step 2: Change the StatusBar Color

Navigate to app > res > values > themes > themes.xml and add the below code under the style section in the themes.xml file.

<item name="android:statusBarColor" tools:targetApi="l">#308d46</item>

Step 3: Working with activity_main.xml

Navigate to the app > res > layout > activity_main.xml and add the below code to the activity_main.xml file. Below is the code for the activity_main.xml file. The activity_main.xml represents the UI part of our application. It Includes two Buttons on which we are going to apply OnClick Listener and a TextView that displays which Button is clicked by the user.

XML

<?xml version="1.0" encoding="utf-8"?>
<!-- LinearLayout orientation vertically !-->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <!-- TextView to display which button is click by the user !-->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        tools:text="Text"
        android:id="@+id/tv_display"
        android:gravity="center"
        android:layout_gravity="center"
        android:layout_marginTop="100dp"
        android:textStyle="bold"
        android:textColor="@color/black"
        android:textSize="20sp" />

    <!--Button 1 !-->
    <Button
        android:layout_width="180dp"
        android:layout_height="40dp"
        android:text="Button 1"
        android:id="@+id/btn1"
        android:layout_gravity="center"
        android:layout_marginTop="190dp" />

    <!--Button 2!-->
    <Button
        android:layout_width="180dp"
        android:layout_height="40dp"
        android:text="Button 2"
        android:id="@+id/btn2"
        android:layout_gravity="center"
        android:layout_marginTop="50dp" />
</LinearLayout>

Step 4: Working with MainActivity File

In this step, we are going to apply the OncClick listener to our two buttons with the help of the when keyword. At first, we have to implement View.OnClickListener to our MainActivity class.

class MainActivity : AppCompatActivity() , View.OnClickListener

Then we have to override the onClick method in our MainActivity class. Then in the onClick method, we are going to use our when keyword. Go to the MainActivity File (Navigate to app > java > YourPackageName > MainActivity) and follow the below code.  Comments are added inside the code for a better understanding of the Code.

Kotlin

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.TextView
import android.widget.Toast

class MainActivity : AppCompatActivity() , View.OnClickListener {
    // Implementing View.OnclickListener
    var tv:TextView?=null
    var btn1:Button?=null
    var btn2:Button?=null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        tv=findViewById(R.id.tv_display)
        btn1=findViewById(R.id.btn1)
        btn2=findViewById(R.id.btn2)
        btn2?.setOnClickListener(this) // Applying onCLick Listener to the button
        btn1?.setOnClickListener(this) // Applying onCLick Listener to the button

    }

    // Overriding onClick Method in our Class
    override fun onClick(view: View?) {
        // passing the id of the button that was clicked by the user
        when(view!!.id){
            // when button 1 is clicked then execute this block of code
            R.id.btn1->{
                Toast.makeText(this,"Button 1 is clicked",Toast.LENGTH_SHORT).show()
                tv?.setText("Button 1 is clicked") //Assign the text to the textview

            }
            // when button 2 is clicked then execute this block of code
            R.id.btn2->{
                Toast.makeText(this,"Button 2 is clicked",Toast.LENGTH_SHORT).show()
                tv?.setText("Button 2 is Clicked") // Assign the text to the textview
            }
        }
    }
}

Java

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    // Implementing View.OnclickListener
    private TextView tv;
    private Button btn1;
    private Button btn2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tv = findViewById(R.id.tv_display);
        btn1 = findViewById(R.id.btn1);
        btn2 = findViewById(R.id.btn2);

        btn2.setOnClickListener(this); // Applying onClick Listener to the button
        btn1.setOnClickListener(this); // Applying onClick Listener to the button
    }

    // Overriding onClick Method in our Class
    @Override
    public void onClick(View view) {
        // passing the id of the button that was clicked by the user
        switch(view.getId()) {
            // when button 1 is clicked then execute this block of code
            case R.id.btn1:
                Toast.makeText(this,"Button 1 is clicked",Toast.LENGTH_SHORT).show();
                tv.setText("Button 1 is clicked"); //Assign the text to the textview
                break;

            // when button 2 is clicked then execute this block of code
            case R.id.btn2:
                Toast.makeText(this,"Button 2 is clicked",Toast.LENGTH_SHORT).show();
                tv.setText("Button 2 is Clicked"); // Assign the text to the textview
                break;
        }
    }
}

Output: