Basket Score

activity_main.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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/tv_score"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="32dp"
        android:textSize="48sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="0 - 0" />

    <TextView
        android:id="@+id/tv_team1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="32dp"
        android:text="@string/team_1"
        android:textSize="24sp"
        app:layout_constraintEnd_toStartOf="@+id/guideline_center"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tv_score" />

    <TextView
        android:id="@+id/tv_team2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="32dp"
        android:text="@string/team_2"
        android:textSize="24sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@+id/guideline_center"
        app:layout_constraintTop_toBottomOf="@+id/tv_score" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline_center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.5" />

    <!-- Team 1 Buttons -->
    <Button
        android:id="@+id/btn_t1_free_throw"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="16dp"
        android:layout_marginTop="16dp"
        android:text="@string/free_throw"
        app:layout_constraintEnd_toStartOf="@+id/guideline_center"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tv_team1" />

    <Button
        android:id="@+id/btn_t1_two_points"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="16dp"
        android:layout_marginTop="16dp"
        android:text="@string/two_points"
        app:layout_constraintEnd_toStartOf="@+id/guideline_center"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btn_t1_free_throw" />

    <Button
        android:id="@+id/btn_t1_three_points"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="16dp"
        android:layout_marginTop="16dp"
        android:text="@string/three_points"
        app:layout_constraintEnd_toStartOf="@+id/guideline_center"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btn_t1_two_points" />

    <!-- Team 2 Buttons -->
    <Button
        android:id="@+id/btn_t2_free_throw"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="16dp"
        android:layout_marginTop="16dp"
        android:text="@string/free_throw"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@+id/guideline_center"
        app:layout_constraintTop_toBottomOf="@+id/tv_team2" />

    <Button
        android:id="@+id/btn_t2_two_points"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="16dp"
        android:layout_marginTop="16dp"
        android:text="@string/two_points"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@+id/guideline_center"
        app:layout_constraintTop_toBottomOf="@+id/btn_t2_free_throw" />

    <Button
        android:id="@+id/btn_t2_three_points"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="16dp"
        android:layout_marginTop="16dp"
        android:text="@string/three_points"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@+id/guideline_center"
        app:layout_constraintTop_toBottomOf="@+id/btn_t2_two_points" />

    <!-- Undo Button -->
    <Button
        android:id="@+id/btn_undo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="32dp"
        android:layout_marginEnd="8dp"
        android:text="@string/undo"
        android:enabled="false"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/guideline_center" />

    <!-- Reset Button -->
    <Button
        android:id="@+id/btn_reset"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="32dp"
        android:layout_marginStart="8dp"
        android:text="@string/reset_score"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@+id/guideline_center" />

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.guiathayde.basketscore;

import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
import androidx.lifecycle.ViewModelProvider;

public class MainActivity extends AppCompatActivity {

    private ScoreViewModel viewModel;
    private TextView tvScore;
    private Button btnUndo;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_main);
        
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
            Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
            return insets;
        });

        viewModel = new ViewModelProvider(this).get(ScoreViewModel.class);

        tvScore = findViewById(R.id.tv_score);
        btnUndo = findViewById(R.id.btn_undo);
        Button btnReset = findViewById(R.id.btn_reset);

        Button btnT1FreeThrow = findViewById(R.id.btn_t1_free_throw);
        Button btnT1TwoPoints = findViewById(R.id.btn_t1_two_points);
        Button btnT1ThreePoints = findViewById(R.id.btn_t1_three_points);

        Button btnT2FreeThrow = findViewById(R.id.btn_t2_free_throw);
        Button btnT2TwoPoints = findViewById(R.id.btn_t2_two_points);
        Button btnT2ThreePoints = findViewById(R.id.btn_t2_three_points);

        // Team 1 actions
        btnT1FreeThrow.setOnClickListener(v -> viewModel.addPoints(1, 1));
        btnT1TwoPoints.setOnClickListener(v -> viewModel.addPoints(1, 2));
        btnT1ThreePoints.setOnClickListener(v -> viewModel.addPoints(1, 3));

        // Team 2 actions
        btnT2FreeThrow.setOnClickListener(v -> viewModel.addPoints(2, 1));
        btnT2TwoPoints.setOnClickListener(v -> viewModel.addPoints(2, 2));
        btnT2ThreePoints.setOnClickListener(v -> viewModel.addPoints(2, 3));

        // Undo action
        btnUndo.setOnClickListener(v -> viewModel.undoLastAction());

        // Reset action
        btnReset.setOnClickListener(v -> viewModel.resetScore());

        // Observe ViewModel
        viewModel.getTeam1Score().observe(this, score -> updateScoreView());
        viewModel.getTeam2Score().observe(this, score -> updateScoreView());
        
        viewModel.getCanUndo().observe(this, canUndo -> btnUndo.setEnabled(canUndo));
    }

    private void updateScoreView() {
        int score1 = viewModel.getTeam1Score().getValue() != null ? viewModel.getTeam1Score().getValue() : 0;
        int score2 = viewModel.getTeam2Score().getValue() != null ? viewModel.getTeam2Score().getValue() : 0;
        
        String scoreText = getString(R.string.score_format, score1, score2);
        tvScore.setText(scoreText);
    }
}

ScoreViewModel.java

package com.guiathayde.basketscore;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class ScoreViewModel extends ViewModel {

    private final MutableLiveData<Integer> team1Score = new MutableLiveData<>(0);
    private final MutableLiveData<Integer> team2Score = new MutableLiveData<>(0);
    private final MutableLiveData<Boolean> canUndo = new MutableLiveData<>(false);

    // Store the last action to be able to undo
    private int lastTeam = 0; // 1 for team 1, 2 for team 2, 0 for none
    private int lastPoints = 0;

    public LiveData<Integer> getTeam1Score() {
        return team1Score;
    }

    public LiveData<Integer> getTeam2Score() {
        return team2Score;
    }

    public LiveData<Boolean> getCanUndo() {
        return canUndo;
    }

    public void addPoints(int team, int points) {
        if (team == 1) {
            Integer currentScore = team1Score.getValue();
            team1Score.setValue((currentScore != null ? currentScore : 0) + points);
        } else if (team == 2) {
            Integer currentScore = team2Score.getValue();
            team2Score.setValue((currentScore != null ? currentScore : 0) + points);
        }

        lastTeam = team;
        lastPoints = points;
        canUndo.setValue(true);
    }

    public void undoLastAction() {
        if (Boolean.TRUE.equals(canUndo.getValue())) {
            if (lastTeam == 1) {
                Integer currentScore = team1Score.getValue();
                team1Score.setValue((currentScore != null ? currentScore : 0) - lastPoints);
            } else if (lastTeam == 2) {
                Integer currentScore = team2Score.getValue();
                team2Score.setValue((currentScore != null ? currentScore : 0) - lastPoints);
            }

            lastTeam = 0;
            lastPoints = 0;
            canUndo.setValue(false);
        }
    }

    public void resetScore() {
        team1Score.setValue(0);
        team2Score.setValue(0);
        lastTeam = 0;
        lastPoints = 0;
        canUndo.setValue(false);
    }
}