Android MotionLayout Tutorial – Collapsing View

MotionLayout is a layout class that extends from ConstraintLayout. MotionLayout has all the features of ConstraintLayout. On top of that, it also provides the ability to easily animate changes to your UI, without needing to know much about UI interactions and the Android Animation Frameworks.

Take for example this subtle animation of a view being scrolled and the profile picture shrinking. Before MotionLayout, this would be a tedious task to complete. We may have needed a CollapsingToolbar and some other custom animation code to ensure the profile picture scales correctly. Now with MotionLayout, this is really easy to achieve with one extra XML file.

In this article, we will be looking at implementing a simple swipe action on a RecyclerView and how we can achieve the scaling animation with MotionLayout.

Add MotionLayout as a Gradle Dependency

To get started with MotionLayout, you need to make sure we have the latest version in your build.gradlefile. (Note: MotionLayout is still in alpha at the time of writing)

 implementation 'androidx.constraintlayout:constraintlayout:2.0.0-alpha3'

Create your layout XML as per usual

The great part about MotionLayout is that it uses the same constructs as ConstraintLayout. Everything you’ve previously learnt about ConstraintLayout (ie barriers, chains etc) is applicable to layouts that we build with MotionLayout.

To get started, open up your editor and change the root element of your layout to use MotionLayout. Add a RecyclerView and an ImageView to your layout. Make sure the RecyclerView is constrained to the bottom of the ImageView.

The XML behind the following layout should look similar to this:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.motion.widget.MotionLayout 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:orientation="vertical"                                android:layout_width="match_parent"                                     app:showPaths="false"                          app:layoutDescription="@xml/motion_layout_example"                                android:layout_height="match_parent">
    <View android:layout_width="0dp" android:layout_height="0dp"
          app:layout_constraintStart_toStartOf="parent"
          android:background="@color/colorPrimary"
          android:id="@+id/background"
          app:layout_constraintBottom_toBottomOf="@id/space"
          app:layout_constraintTop_toTopOf="parent"
          app:layout_constraintEnd_toEndOf="parent" android:alpha="0"
    />

    <ImageView
            android:layout_width="140dp"
            android:layout_height="0dp"
            android:scaleType="centerCrop"
            android:id="@+id/imageViewAvatar"
            android:layout_marginTop="16dp"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginStart="16dp"
            app:layout_constraintDimensionRatio="h,1:1"
            app:srcCompat="@drawable/veruca"/>


    <TextView
            android:text="@string/veruca_salt_name"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:id="@+id/textViewName"
            android:fontFamily="@font/willywonka"
            app:layout_constraintStart_toEndOf="@+id/imageViewAvatar"
            android:layout_marginStart="16dp"
            app:layout_constraintEnd_toEndOf="parent"
            android:layout_marginEnd="16dp"
            android:textAppearance="@style/TextAppearance.AppCompat.Display1"
            android:layout_marginTop="8dp"
            app:layout_constraintTop_toTopOf="@+id/imageViewAvatar" 
            android:layout_marginBottom="8dp"
            app:layout_constraintBottom_toTopOf="@+id/space"/>

    <androidx.recyclerview.widget.RecyclerView
            android:layout_width="0dp"
            android:layout_height="0dp"
            app:layout_constraintEnd_toEndOf="parent"
            android:layout_marginEnd="8dp"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginStart="8dp"
            app:layout_constraintBottom_toBottomOf="parent"
            tools:listitem="@layout/list_item_status"
            android:id="@+id/recyclerViewStatus" android:layout_marginTop="8dp"
            app:layout_constraintTop_toBottomOf="@+id/imageViewAvatar">

    </androidx.recyclerview.widget.RecyclerView>
    <Space
            android:layout_width="0dp"
            android:layout_height="8dp"
            android:id="@+id/space"
            app:layout_constraintStart_toEndOf="@+id/imageViewAvatar"
            app:layout_constraintTop_toBottomOf="@id/imageViewAvatar"
            app:layout_constraintEnd_toEndOf="@+id/imageViewAvatar"
            app:layout_constraintStart_toStartOf="@+id/imageViewAvatar"/>
</androidx.constraintlayout.motion.widget.MotionLayout>

Create the MotionScene XML

In order to animate this layout we need to describe how views should animate in the layout. To do this, create an XML file in the xml folder of your application. We will call it motion_scene.xml.

The first thing that we will do, is define the Transition for this MotionScene. We set the reference to the start and end ConstraintSets on the Transition object. We can also set the duration of the transition.

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

    <Transition
            app:constraintSetStart="@id/start"
            app:constraintSetEnd="@id/end"
            app:duration="1000">
        <OnSwipe
                app:touchAnchorId="@+id/recyclerViewStatus"
                app:touchAnchorSide="top"
                app:dragDirection="dragUp" />
    </Transition>
    <ConstraintSet android:id="@+id/start">
    </ConstraintSet>

    <ConstraintSet android:id="@+id/end">
    </ConstraintSet>
</MotionScene>

The next step, that can be seen in the code snippet above, is to create the OnSwipe declaration. This indicates to the MotionLayout that it should monitor the layout for a swipe movement. When the user performs a dragUp gesture on the specified touchAnchorId, the MotionScene will start interpolating between the two states defined (start and end). In this case, it is the recyclerViewStatus view that it will be monitoring for the dragUp gesture.

In the code snippet above, you may notice that there are two ConstraintSet tags defined in the MotionScene. These tags are for the start and end constraints of the view. The beautiful part about MotionLayout is that it will automatically interpolate between these two states and produce some pretty magical animations. At the moment, we don’t have any constraint changes applied, so let’s change that.

The first view we want to animate is the ImageView. We want the size of the view to decrease as a user scrolls up on the RecyclerView. To do that, we will add an end Constraint to the ImageView to adjust the width and height to 40dp .

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

    <Transition
            app:constraintSetStart="@id/start"
            app:constraintSetEnd="@id/end"
            app:duration="1000">
        <OnSwipe
                app:touchAnchorId="@+id/recyclerViewStatus"
                app:touchAnchorSide="top"
                app:dragDirection="dragUp" />
    </Transition>

    <ConstraintSet android:id="@+id/start">

    </ConstraintSet>

    <ConstraintSet android:id="@+id/end">
        
        <Constraint android:id="@id/imageViewAvatar"
                    android:layout_width="40dp"
                    android:layout_height="40dp" android:layout_marginTop="16dp"
                    app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
                    android:layout_marginStart="16dp">
        </Constraint>

    </ConstraintSet>
</MotionScene>

Linking the MotionScene to the Layout

In order to link the MotionScene to the Layout, you will need to set the property app:layoutDescription="@xml/motion_layout_example" to point to your newly created XML file on the root MotionLayout element.

Running this on device, you will observe that as you scroll up on the RecyclerView , the ImageView decreases in size.

Animating Visibility of a View

Now if you wanted to animate the background to go from invisible to visible, we can just add a Property animation to the start and end constraints. The final XML will look as follows:

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

    <Transition
            app:constraintSetStart="@id/start"
            app:constraintSetEnd="@id/end"
            app:duration="1000">
        <OnSwipe
                app:touchAnchorId="@+id/recyclerViewStatus"
                app:touchAnchorSide="top"
                app:dragDirection="dragUp" />
    </Transition>

    <ConstraintSet android:id="@+id/start">

        <Constraint android:id="@id/background">
            <PropertySet app:alpha="0"/>
        </Constraint>
    </ConstraintSet>

    <ConstraintSet android:id="@+id/end">

        <Constraint android:id="@id/imageViewAvatar"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:layout_marginTop="16dp"
                    app:layout_constraintTop_toTopOf="parent"
                    app:layout_constraintStart_toStartOf="parent"
                    android:layout_marginStart="16dp">
        </Constraint>

        <Constraint android:id="@id/background">
            <PropertySet app:alpha="1"/>
        </Constraint>
    </ConstraintSet>
</MotionScene>

It’s a wrap!

As you can see from the short example above, using MotionLayout can decrease the amount of code you need to write in order to achieve delightful animations. In the next few posts, we will be covering more of the features of MotionLayout, as this article has just touched the surface. Till next time!

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