Android

Implementing a RatingBar in Android Using Kotlin and Java

In this comprehensive tutorial, you will learn how to develop an Android application that incorporates a RatingBar using both Kotlin and Java. The tutorial provides a detailed, step-by-step guide to help you set up the layout XML file and implement functionality to manage user interactions with the RatingBar effectively.
Submitted on July 07, 2024

Creating an Android app with a RatingBar in both Kotlin and Java involves setting up the layout XML file and then implementing functionality in the respective language for handling user interactions and displaying the rating. Below are step-by-step instructions for both Kotlin and Java:

Step 1: Set up the Project and Layout

  1. Create Project: Start a new Android Studio project with an Empty Activity.

  2. Layout (‘res/layout/activity_main.xml’): Design the main activity layout with a RatingBar and a TextView to display the rating.

        
            <?xml version="1.0" encoding="utf-8"?>
            <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:padding="16dp">

                <RatingBar
                    android:id="@+id/ratingBar"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:numStars="5"
                    android:rating="0"
                    android:stepSize="1"
                    android:layout_centerHorizontal="true" />

                <TextView
                    android:id="@+id/tvRating"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="Rating: 0"
                    android:textSize="18sp"
                    android:layout_below="@id/ratingBar"
                    android:layout_centerHorizontal="true"
                    android:layout_marginTop="16dp"/>
                
            </RelativeLayout>

Kotlin Implementation

Step 2: Implement MainActivity (MainActivity.kt)

  1. Implement MainActivity (‘MainActivity.kt’):

        
            import androidx.appcompat.app.AppCompatActivity;
            import android.os.Bundle;
            import android.widget.RatingBar;
            import android.widget.TextView;

            class MainActivity : AppCompatActivity() {

                private lateinit var ratingBar: RatingBar
                private lateinit var tvRating: TextView

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

                    ratingBar = findViewById(R.id.ratingBar)
                    tvRating = findViewById(R.id.tvRating)

                    ratingBar.setOnRatingBarChangeListener { _, rating, _ ->
                        tvRating.text = "Rating: $rating"
                    }
                }
            }

Java Implementation

Step 2: Implement MainActivity (MainActivity.java)

  1. Implement MainActivity (MainActivity.java):

    2. Handle RatingBar changes and update the TextView accordingly.

            
            import androidx.appcompat.app.AppCompatActivity;
            import android.os.Bundle;
            import android.widget.RatingBar;
            import android.widget.TextView;

            public class MainActivity extends AppCompatActivity {

                private RatingBar ratingBar;
                private TextView tvRating;

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

                    ratingBar = findViewById(R.id.ratingBar);
                    tvRating = findViewById(R.id.tvRating);

                    ratingBar.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() {
                        @Override
                        public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) {
                            tvRating.setText("Rating: " + rating);
                        }
                    });
                }
            }

    Explanation:

    • Both Kotlin and Java implementations follow the same logic:
      • The layout (activity_main.xml) contains a RatingBar and a TextView.
      • In the MainActivity, the RatingBar is initialized and an OnRatingBarChangeListener is set to update the TextView (tvRating) whenever the rating changes.

    Additional Notes:

    • Ensure you have the necessary imports (import android.widget.RatingBar; and import android.widget.TextView;).
    • Both Kotlin and Java code snippets assume basic familiarity with Android development, such as setting up activities and handling UI components.

    By following these steps, you can create a simple Android app with a RatingBar that updates a TextView to display the selected rating, demonstrating how to handle user input and update UI elements accordingly in both Kotlin and Java.