Change Background With A Touch

 This tutorial is the simplest example of changing the background color with a touch.

First start with the xml file i.e activity_main.xml

In actual you don't really have to do anything in the xml file but just for understanding, just type this line in the base / Constraint Layout

android:background="@color/white"

So that the complete xml script becomes:

<?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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/white"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

It already has the id defined so no worries.

Now let's move on to the Java code i.e MainActivity.java file:

Here create an object of Constraint Layout

ConstraintLayout cl;

and initialize it in the onCreate method

cl = findViewById(R.id.main);

finally in the onUserInteraction method, just set the color you want

cl.setBackgroundColor(Color.WHITE);

If you want random colors on every interaction, just create an array of colors in this way with a random object:

int[] color = {Color.BLUE, Color.CYAN, Color.MAGENTA,
    Color.BLACK, Color.GRAY, Color.GREEN, Color.RED};
Random random = new Random();

In onUserInteraction use the random object to set a random color:

cl.setBackgroundColor(color[random.nextInt(color.length-1)]);

So now the complete Java code becomes:

package com.example.backgroundcolorchanger;

import android.graphics.Color;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;
import java.util.Random;

public class MainActivity extends AppCompatActivity {

    ConstraintLayout cl;
    int[] color = {Color.BLUE, Color.CYAN, Color.MAGENTA,
        Color.BLACK, Color.GRAY, Color.GREEN, Color.RED};
    Random random = new Random();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        cl = findViewById(R.id.main);
    }

    @Override
    public void onUserInteraction() {
        super.onUserInteraction();
        cl.setBackgroundColor(color[random.nextInt(color.length-1)]);
    }
}