RatingBar in Kotlin

Android RatingBar is a user interface widget which is used to get the rating from the customers or users. It is an extension of SeekBar and ProgressBar that shows star ratings and it allow users to give the rating by clicking on the stars.

In RatingBar, we can set the step size using android:stepSize and it will always return a rating value as floating point number such as 1.0, 2.0, 2.5 etc. By using, android:numStars attribute we can specify the number of stars in RatingBar. RatingBar is used to get ratings form users or customers about the product, movie or hotel experience etc.

RatingBar can be created manually or programmatically but we are going to discuss manually.

First we create a new project by following the below steps:

1. Click on File, then New => New Project.
2. After that include the Kotlin support and click on next.
3. Select the minimum SDK as per convenience and click next button.
4. Then select the Empty activity => next => finish.

Different Attributes of RatingBar Widget

XML Attributes	Description
android:id	Used to uniquely identify the control.
android:rating	Used to set the default rating value for ratingbar.
android:numStars	Used to set number of stars to display.
android:background	Used to set the background color for Ratingbar.
android:padding	Used to set the padding for left, right, top or bottom of Ratingbar.
android:stepSize	Used to set the step size on RatingBar like 0.5 or 1.

Modify the activity_main.xml file

In this file, we add RatingBar and button in the LinearLayout. Also set attributes for both of the widgets like id, stepSize, background etc.

xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:gravity ="center">

    <RatingBar
        android:id="@+id/rBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:stepSize="0.5"
        android:theme="@style/Widget.AppCompat.RatingBar"
        android:background="@color/colorPrimary"
        android:numStars="4"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Submit Rating" />

</LinearLayout>

Name of the application can be put in strings.xml file

xml

<resources>
    <string name="app_name">RatingkBarInKotlin</string>
</resources>

Access the RatingBar in MainActivity.kt file

First, we will declare the variable rBar to access the Rating using the id like

val rBar = findViewById<RatingBar>(R.id.rBar)

then, declare another variable button and access the button using its id.

val button = findViewById<Button>(R.id.button)

In the end, to display toast msg while submitting the ratings we code like this

button?.setOnClickListener {
      val msg = rBar.rating.toString()
      Toast.makeText(this@MainActivity,
       "Rating is: "+msg, Toast.LENGTH_SHORT).show()

Kotlin

package com.geeksforgeeks.myfirstkotlinapp

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.RatingBar
import android.widget.Toast

class MainActivity : AppCompatActivity() {

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

        val rBar = findViewById<RatingBar>(R.id.rBar)
        if (rBar != null) {
            val button = findViewById<Button>(R.id.button)
            button?.setOnClickListener {
                val msg = rBar.rating.toString()
                Toast.makeText(this@MainActivity,
                    "Rating is: "+msg, Toast.LENGTH_SHORT).show()
            }
        }
    }
}

AndroidManifest.xml file

xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.geeksforgeeks.myfirstkotlinapp">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

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