// Main Acitivity.java

package com.example.firebaseconnection;

import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import androidx.activity.EdgeToEdge;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

import com.google.firebase.FirebaseApp;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Objects;

public class MainActivity extends AppCompatActivity {

private TextView titleId;
private EditText stdId,stdName,stdAge,course;
private Button submitBtn, submitBtn1;

//Data Base Connection
private DatabaseReference databaseReference;


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

        //FireBase
        FirebaseApp.initializeApp(this);

        //Wiring Part
        titleId = findViewById(R.id.titleId);
        stdId = findViewById(R.id.stdID);
        stdName = findViewById(R.id.stdName);
        stdAge = findViewById(R.id.stdAge);
        course = findViewById(R.id.course);
        submitBtn = findViewById(R.id.submitBtn);
        submitBtn1 = findViewById(R.id.submitBtn1);


        //Fire Base Connection

        databaseReference = FirebaseDatabase.getInstance().getReference("Student");
        //FirebaseDatabase.getInstance() - url is created
        //https://sensoriotmobileapp-default-rtdb.firebaseio.com/

        //getReference("Student") --> we are creating collection name is Student

        submitBtn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, MainActivity2.class);
                startActivity(intent);
            }
        });

        submitBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                //Getting user inputs from the UI we created
                String name = stdName.getText().toString().trim();
                String age = stdAge.getText().toString().trim();
                String course1 = course.getText().toString().trim();


                if (TextUtils.isEmpty(name) || TextUtils.isEmpty(age) || TextUtils.isEmpty(course1)) {
                    Toast.makeText(MainActivity.this, "Field are Empty, Please fill it", Toast.LENGTH_SHORT).show();
                }

                //Reformat it which will accept for the firebase database. in here we can use HashMap

                HashMap<String, Object> studentData = new HashMap<String, Object>();

                // Formating the data as key value pair
                studentData.put("name",name);
                studentData.put("age",age);
                studentData.put("course", course1);


                // Adding the hashmap value into the firebase database
                databaseReference.setValue(studentData, new DatabaseReference.CompletionListener() {
                    @Override
                    public void onComplete(@Nullable DatabaseError error, @NonNull DatabaseReference ref) {

                        if (error == null){
                            Toast.makeText(MainActivity.this, "Successfully Added.", Toast.LENGTH_SHORT).show();
                        }
                        else {
                            Toast.makeText(MainActivity.this, "Failed to Add data.", Toast.LENGTH_SHORT).show();
                        }

                    }
                });

            }
        });
    }
}


//activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<ScrollView 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:padding="24dp"
    android:background="@android:color/white"
    tools:context=".MainActivity">

    <LinearLayout
        android:id="@+id/main"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:gravity="center_horizontal">

        <TextView
            android:id="@+id/titleId"
            android:text="IoT Mobile App"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="@android:color/black"
            android:textSize="32sp"
            android:textStyle="bold"
            android:layout_marginBottom="24dp" />

        <EditText
            android:id="@+id/stdID"
            android:hint="Enter Student ID"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="text"
            android:padding="12dp"
            android:background="@drawable/edittext_background"
            android:layout_marginBottom="16dp" />

        <EditText
            android:id="@+id/stdName"
            android:hint="Enter Student Name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="textPersonName"
            android:padding="12dp"
            android:background="@drawable/edittext_background"
            android:layout_marginBottom="16dp" />

        <EditText
            android:id="@+id/stdAge"
            android:hint="Enter Student Age"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:padding="12dp"
            android:background="@drawable/edittext_background"
            android:layout_marginBottom="16dp" />

        <EditText
            android:id="@+id/course"
            android:hint="Enter the Course"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="text"
            android:padding="12dp"
            android:background="@drawable/edittext_background"
            android:layout_marginBottom="24dp" />

        <Button
            android:id="@+id/submitBtn"
            android:text="Submit"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:backgroundTint="@color/black"
            android:textColor="@android:color/white"
            android:paddingVertical="12dp"
            android:layout_marginTop="16dp"
            android:background="@drawable/button_background" />

        <Button
            android:id="@+id/submitBtn1"
            android:text="Next Page Button"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:backgroundTint="@color/black"
            android:textColor="@android:color/white"
            android:paddingVertical="12dp"
            android:layout_marginTop="16dp"
            android:background="@drawable/button_background" />


    </LinearLayout>
</ScrollView>


//Main_Activity2. java
package com.example.firebaseconnection;

import android.os.Bundle;
import android.widget.EditText;

import androidx.activity.EdgeToEdge;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

import com.google.firebase.FirebaseApp;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class MainActivity2 extends AppCompatActivity {

    private DatabaseReference databaseReference;

    private EditText name1,age1,course1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        //FireBase
        FirebaseApp.initializeApp(this);

        name1 = (EditText) findViewById(R.id.nameVal);
        age1 = (EditText) findViewById(R.id.ageVal);
        course1 = (EditText) findViewById(R.id.courseVal);

        databaseReference = FirebaseDatabase.getInstance().getReference("Student");

        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()){
                    String name = snapshot.child("name").getValue(String.class);
                    String age = snapshot.child("age").getValue(String.class);
                    String course = snapshot.child("course").getValue(String.class);

                    name1.setText(name);
                    age1.setText(age);
                    course1.setText(course);

                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

    }
}


//activity_main2.xml
<?xml version="1.0" encoding="utf-8"?>
<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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="24dp"
    android:background="#F5F5F5"
    tools:context=".MainActivity2">

    <TextView
        android:id="@+id/titleId"
        android:text="Firebase Data"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#212121"
        android:textSize="28sp"
        android:textStyle="bold"
        android:layout_marginBottom="32dp" />

    <EditText
        android:id="@+id/nameVal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="12dp"
        android:background="@android:drawable/editbox_background"
        android:layout_marginBottom="16dp" />

    <EditText
        android:id="@+id/ageVal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="12dp"
        android:background="@android:drawable/editbox_background"
        android:layout_marginBottom="16dp" />

    <EditText
        android:id="@+id/courseVal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="12dp"
        android:background="@android:drawable/editbox_background"
        android:layout_marginBottom="16dp" />

</LinearLayout>