Android Programming Lab

Create a simple application to change colors of background of any textbox with the click of a button.

                        
package com.example.myapplication;

import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private String colors[] = {"#FF9800","#03A9F4", "#9067D9", "#FFEB3B"};
    private int i = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_main);
        Button myBtn = findViewById(R.id.button);
        TextView myTxt = findViewById(R.id.textView);
        myBtn.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v) {
                myTxt.setBackgroundColor(Color.parseColor(colors[i]));
                i++;
                if(i>3){
                    i = 0;
                }
            }
        });
    }

}

                        
<?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"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#5DE063"
        android:text="Button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.462"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.522" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="252dp"
        android:background="#FFEB3B"
        android:text="Changing Background Colors"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.456"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />

</androidx.constraintlayout.widget.ConstraintLayout>

Create a simple app to change background colour on button click.

                        
package com.example.myapplication;

import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout; // Import ConstraintLayout

public class MainActivity extends AppCompatActivity {
    // Array of colors to change the background
    private String colors[] = {"#FF9800", "#03A9F4", "#9067D9", "#FFEB3B"};
    private int i = 0; // Index for the colors array

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); // Set the content view to the layout defined in XML

        // Directly cast the main layout to ConstraintLayout
        ConstraintLayout mainLayout = findViewById(R.id.main);
        Button myBtn = findViewById(R.id.button);

        // Set the click listener on the button
        myBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Change the background color of the main layout
                mainLayout.setBackgroundColor(Color.parseColor(colors[i]));
                i++; // Move to the next color
                if (i > 3) {
                    i = 0; // Reset to the first color if out of bounds
                }
            }
        });
    }
}

                        
<?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"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#5DE063"
        android:text="Click Me to change Background Color"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.462"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.522" />

</androidx.constraintlayout.widget.ConstraintLayout>

Create a simple app to add two numbers.

                        
package com.example.myapplication;

import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public void funcAdd(View view)
    {
        EditText et1 = findViewById(R.id.num1);
        EditText et2 = findViewById(R.id.num2);
        int num1 = Integer.parseInt(et1.getText().toString());
        int num2 = Integer.parseInt(et2.getText().toString());
        int sum = num1 + num2;
        TextView tv1 = findViewById(R.id.text1);
        tv1.setText(sum + "");
    }
}

                        
<?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"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/text1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Answer"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.523" />

    <EditText
        android:id="@+id/num1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Number 1"
        android:inputType="number"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.051" />

    <EditText
        android:id="@+id/num2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Number 2"
        android:inputType="number"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.173" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Add"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:onClick="funcAdd"
        app:layout_constraintVertical_bias="0.32" />

</androidx.constraintlayout.widget.ConstraintLayout>

Note: Make sure to add android:onClick="funcAdd" to the button in your XML file.

Create a simple app to create a simple calculator.

                        
package com.example.myapplication;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    private EditText editTextNumber1;
    private EditText editTextNumber2;
    private TextView textViewResult;

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

        editTextNumber1 = findViewById(R.id.editTextNumber);
        editTextNumber2 = findViewById(R.id.editTextNumber2);
        textViewResult = findViewById(R.id.textViewResult);

        Button buttonAdd = findViewById(R.id.buttonAdd);
        Button buttonSubtract = findViewById(R.id.buttonSubtract);
        Button buttonMultiply = findViewById(R.id.buttonMultiply);
        Button buttonDivide = findViewById(R.id.buttonDivide);

        // Set up the listeners for the buttons
        buttonAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                calculate('+');
            }
        });

        buttonSubtract.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                calculate('-');
            }
        });

        buttonMultiply.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                calculate('*');
            }
        });

        buttonDivide.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                calculate('/');
            }
        });
    }

    private void calculate(char operator) {
        // Get input numbers
        double num1 = Double.parseDouble(editTextNumber1.getText().toString());
        double num2 = Double.parseDouble(editTextNumber2.getText().toString());
        double result = 0;

        // Perform calculation based on the operator
        switch (operator) {
            case '+':
                result = num1 + num2;
                break;
            case '-':
                result = num1 - num2;
                break;
            case '*':
                result = num1 * num2;
                break;
            case '/':
                if (num2 != 0) {
                    result = num1 / num2;
                } else {
                    textViewResult.setText("Cannot divide by zero!");
                    return;
                }
                break;
        }

        // Display the result
        textViewResult.setText("Result: " + result);
    }
}

                        
<?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"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editTextNumber"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:hint="Enter number"
        android:inputType="numberDecimal"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp" />

    <EditText
        android:id="@+id/editTextNumber2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:hint="Enter another number"
        android:inputType="numberDecimal"
        app:layout_constraintTop_toBottomOf="@+id/editTextNumber"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp" />

    <Button
        android:id="@+id/buttonAdd"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Add"
        app:layout_constraintTop_toBottomOf="@+id/editTextNumber2"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp" />

    <Button
        android:id="@+id/buttonSubtract"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Subtract"
        app:layout_constraintTop_toBottomOf="@+id/buttonAdd"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp" />

    <Button
        android:id="@+id/buttonMultiply"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Multiply"
        app:layout_constraintTop_toBottomOf="@+id/buttonSubtract"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp" />

    <Button
        android:id="@+id/buttonDivide"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Divide"
        app:layout_constraintTop_toBottomOf="@+id/buttonMultiply"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp" />

    <TextView
        android:id="@+id/textViewResult"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Result: "
        android:textSize="18sp"
        app:layout_constraintTop_toBottomOf="@+id/buttonDivide"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

Create an app to set image on imageview.

                        
package com.example.myapplication;

import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    // Declare the ImageView
    ImageView imageView;

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

        // Initialize the ImageView
        imageView = findViewById(R.id.imageView);
    }

    // Method to set the image on ImageView when the button is clicked
    public void setImage(View view) {
        // Set the image resource from the drawable folder
        imageView.setImageResource(R.drawable.sample_image);
    }
}

                        
<?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"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="50dp"
        android:contentDescription="Sample Image"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

    <Button
        android:id="@+id/btnSetImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Set Image"
        android:layout_marginTop="20dp"
        android:onClick="setImage"
        app:layout_constraintTop_toBottomOf="@+id/imageView"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

Note: Place your image in the res/drawable folder. You can do this by copying an image into the drawable directory in Android Studio

Create a program to change image on button click.

                        
package com.example.imageswitcherapp;

import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    // Declare the ImageView
    ImageView imageView;

    // Flag to track which image is currently displayed
    boolean isImage1 = true;

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

        // Initialize the ImageView
        imageView = findViewById(R.id.imageView);
    }

    // Method to change the image on ImageView when the button is clicked
    public void changeImage(View view) {
        if (isImage1) {
            // Change to the second image
            imageView.setImageResource(R.drawable.sample_image2);
        } else {
            // Change back to the first image
            imageView.setImageResource(R.drawable.sample_image);
        }
        // Toggle the flag
        isImage1 = !isImage1;
    }
}

                        
<?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"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="198dp"
        android:layout_height="393dp"
        android:layout_marginTop="28dp"
        android:contentDescription="Image"
        android:src="@drawable/sample_image"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnChangeImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="200dp"
        android:onClick="changeImage"
        android:text="Change Image"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.555"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView" />
</androidx.constraintlayout.widget.ConstraintLayout>