Android Rotate animations in Kotlin

Rotate animation is a special kind of animation in Android which controls the Rotation of an object. These type of animations are usually used by developers to give a feel to the user about the changes happening in the application like loading content, processing data, etc. By using the rotate animation effect, an object can be rotated in the X-Y plane of activity and it allows the rotation in both Clockwise and Anticlockwise direction. 

The class hierarchy of RotateAnimation class in Kotlin

XML attributes which define the rotation of an object

XML Attributes	Description
android:pivotX	To define the X coordinate of the point about which the object is being rotated
android:pivotY	To define the Y coordinate of the point about which the object is being rotated
android:fromDegrees	Rotation of the object starts from this geometrical degree
android:toDegrees	Rotation of the object ends at this geometrical degree
android:duration	Used to define the duration of the animation in millisecond
android:startOffset	Used to delay the animation time in millisecond

Approach

This example demonstrates the steps involved in implementing the clockwise and anticlockwise rotation animation to an image file. An image file will be added in the activity using ImageView.

Note: The steps are performed on Android Studio version 4.0

Step 1: Create a New Project

1. Click on File, then New => New Project.
2. Select language as Kotlin.
3. Select the minimum SDK as per your need.

Step 2: Modify activity_main.xml file

Below is the code for activity_main.xml file to add a TextView, ImageView, and 2 buttons in an activity.

Filename: activity_main.xml

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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#168BC34A"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:fontFamily="@font/roboto"
        android:text="@string/heading"
        android:textAlignment="center"
        android:textColor="@android:color/holo_green_dark"
        android:textSize="36sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.050000012" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="243dp"
        android:layout_height="241dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"
        app:layout_constraintVertical_bias="0.19999999"
        app:srcCompat="@drawable/logo" />

    <Button
        android:id="@+id/clk_rotate_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#AB4CAF50"
        android:fontFamily="@font/roboto"
        android:text="@string/clk_rotate_button_text"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.12"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView"
        app:layout_constraintVertical_bias="0.7" />

    <Button
        android:id="@+id/anticlk_rotate_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#AB4CAF50"
        android:fontFamily="@font/roboto"
        android:text="@string/anticlk_rotate_button_text"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.78"
        app:layout_constraintStart_toEndOf="@+id/clk_rotate_button"
        app:layout_constraintTop_toBottomOf="@+id/imageView"
        app:layout_constraintVertical_bias="0.7" />
</androidx.constraintlayout.widget.ConstraintLayout>

Step 3: Define XML file for clockwise and anticlockwise rotation of the image
Create a new directory in the res folder of the application and name it anim. In this directory create 2 Animation Resource File namely rotate_clockwise and rotate_anticlockwise. These 2 files are the XML file which holds the details of the animation. Below is the code for both the file. 

Filename: rotate_clockwise.xml

XML

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

    <rotate
        android:pivotX = "50%"
        android:pivotY = "50%"
        android:fromDegrees = "0"
        android:toDegrees = "360"
        android:duration = "2500"/>

</set>

Filename: rotate_anticlockwise.xml

XML

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

    <rotate
        android:pivotX = "50%"
        android:pivotY = "50%"
        android:fromDegrees = "360"
        android:toDegrees = "0"
        android:duration = "2500"/>

</set>

Step 4: Modify MainActivity.kt File
Below is the code for MainActivity.kt file to load and start the animation on the ImageView widget according to the button clicked by the user.

Filename: MainActivity.kt

Java

package com.example.androidrotateanimation

import android.os.Bundle
import android.view.animation.AnimationUtils
import android.widget.Button
import android.widget.ImageView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

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

        // assigning id of button which rotates
        // the image in clockwise direction
        val clk_button: Button = findViewById(R.id.clk_rotate_button)

        // assigning id of button which rotates
        // the image in anti-clockwise direction
        val anticlk_button: Button = findViewById(R.id.anticlk_rotate_button)

        // assigning id of imageview
        // which is to be rotated
        val image: ImageView = findViewById(R.id.imageView)

        // actions to be performed when
        // "rotate clockwise" button is clicked
        clk_button.setOnClickListener()
        {

            // loading the animation of
            // rotate_clockwise.xml file into a variable
            val clk_rotate = AnimationUtils.loadAnimation(
                this,
                R.anim.rotate_clockwise
            )

            // assigning that animation to
            // the image and start animation
            image.startAnimation(clk_rotate)
        }

        // actions to be performed when
        // "rotate anticlockwise" button is clicked
        anticlk_button.setOnClickListener()
        {

            // loading the animation of
            // rotate_anticlockwise.xml file into a variable
            val anticlk_rotate = AnimationUtils.loadAnimation(
                this,
                R.anim.rotate_anticlockwise
            )

            // assigning that animation to
            // the image and start animation
            image.startAnimation(anticlk_rotate)
        }
    }
}

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