Button in Android

In Android applications, a Button is a user interface that is used to perform some action when clicked or tapped. It is a very common widget in Android and developers often use it. This article demonstrates how to create a button in Android Studio.

The Class Hierarchy of the Button Class in Kotlin

XML Attributes of Button Widget

XML Attributes	Description
android:id	Used to specify the id of the view.
android:text	Used to the display text of the button.
android:textColor	Used to the display color of the text.
android:textSize	Used to the display size of the text.
android:textStyle	Used to the display style of the text like Bold, Italic, etc.
android:textAllCaps	Used to display text in Capital letters.
android:background	Used to set the background of the view.
android:padding	Used to set the padding of the view.
android:visibility	Used to set the visibility of the view.
android:gravity	Used to specify the gravity of the view like center, top, bottom, etc

Example

In this example step by step demonstration of creating a Button will be covered. The application will consist of a button that displays a toast message when the user taps on it.

Note: Following steps are performed on Android Studio version 4.0

Step 1: Create a new project

1. Click on File, then New => New Project.
2. Choose “Empty Activity” for the project template.
3. Select language as Kotlin.
4. Select the minimum SDK as per your need.

Step 2: Modify the strings.xml file

Navigate to the strings.xml file under the “values” directory of the resource folder. This file will contain all strings that are used in the Application. Below is the appropriate code.

XML

<resources>
    <string name="app_name">GfG | Button In Kotlin</string>
    <string name="btn">Button</string>
    <string name="message">Hello Geeks!! This is a Button.</string>
</resources>

Step 3: Modify the activity_main.xml file

Add a button widget in the layout of the activity. Below is the code of the activity_main.xml file which does the same.  

XML

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    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:background="#168BC34A"
    tools:context=".MainActivity">

    <!-- Button added in the activity -->
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#4CAF50"
        android:paddingStart="10dp"
        android:paddingEnd="10dp"
        android:text="@string/btn"
        android:textColor="@android:color/background_light"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Step 4: Accessing the button in the MainActivity file

Add functionality of button in the MainActivity file. Here describe the operation to display a Toast message when the user taps on the button. Below is the code to carry out this task. 

Java

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

public class MainActivity extends AppCompatActivity {

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

        // storing ID of the button
        // in a variable
        Button button = (Button)findViewById(R.id.button);

        // operations to be performed
        // when user tap on the button
        if (button != null) {
            button.setOnClickListener((View.OnClickListener)(new View.OnClickListener() {
                    public final void onClick(View it) {

                    // displaying a toast message
                    Toast.makeText((Context)MainActivity.this, R.string.message, Toast.LENGTH_LONG).show();
                }
            }));
        }
    }
}

Kotlin

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

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // storing ID of the button
        // in a variable
        val button = findViewById<Button>(R.id.button)

        // operations to be performed
        // when user tap on the button
        button?.setOnClickListener()
        {
            // displaying a toast message
            Toast.makeText(this@MainActivity, R.string.message, Toast.LENGTH_LONG).show() }
    }
}

Output: