Creating Animations With MotionLayout for Android

This tutorial demonstrates how to easily animate widgets in your Android app using MotionLayout, a significant improvement over previous, more cumbersome methods. MotionLayout, part of ConstraintLayout 2.0 and above, simplifies creating custom transitions.

To begin, ensure your layout uses ConstraintLayout version 2.0.0 or higher. The easiest way to integrate MotionLayout is by switching your layout view in Android Studio from "Code" to "Design" or "Split" view. This reveals the Component Tree panel, where you can add a MotionLayout element. We'll add a button labeled "Jump" below a TextView – clicking this button will trigger the animation.

The core of the animation is defined in a MotionScene file (e.g., activity_main_scene.xml). This XML file uses ConstraintSet tags to define the widget's starting and ending states. Here's a simplified example:

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

    <Transition
        motion:constraintSetEnd="@+id/end"
        motion:constraintSetStart="@+id/start"
        motion:duration="200"
        motion:motionInterpolator="easeIn">
        <OnClick motion:targetId="@+id/button" motion:clickAction="transitionToEnd" />
    </Transition>

    <ConstraintSet android:id="@+id/start">
        <Constraint android:id="@+id/textView">
            <CustomAttribute motion:attributeName="textColor" motion:customColorValue="@color/black" />
        </Constraint>
    </ConstraintSet>

    <ConstraintSet android:id="@+id/end">
        <Constraint android:id="@+id/textView"
            android:scaleX="2"
            android:scaleY="2">
            <Layout
                android:layout_marginBottom="40sp"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                motion:layout_constraintBottom_toTopOf="@id/button" />
            <CustomAttribute motion:attributeName="textColor" motion:customColorValue="@color/teal_700" />
        </Constraint>
    </ConstraintSet>

</MotionScene>

This MotionScene defines a transition that scales the TextView to twice its size and changes its color when the button is clicked. The OnClick tag triggers the transition. The ConstraintSet tags specify the initial ("start") and final ("end") states.

In your activity's Kotlin code, you'll need to trigger the animation. This is done by referencing the MotionLayout and calling transitionToEnd():

fun start(v: View) {
    val motionContainer = findViewById<MotionLayout>(R.id.motion_container)
    motionContainer.transitionToEnd()
}

For more complex animations, consider using Android Studio's Motion Editor for visual design. This allows you to create and preview animations without writing all the XML manually. You can also add TransitionListener to execute code at various stages of the animation.

This approach offers granular control over your animations, allowing for sophisticated transitions and event handling within the animation lifecycle. Remember to replace placeholder image URLs with actual image paths.

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