MotionLayout添加3个及以上CustomAttribute时抛出ArrayIndexOutOfBoundsException

I ran into a frustrating issue while working with MotionLayout in Android: adding a 3rd customColorValue, customIntegerValue, or customFloatValue in a MotionScene triggers an ArrayIndexOutOfBoundsException from the MotionController. Here's everything you need to know to reproduce and understand the problem:

Problem Overview #

When defining 3 or more custom attributes with color/integer/float values in a ConstraintSet within a MotionScene, the app crashes immediately. The exception indicates the array length is 2 but we're trying to access index 2, and it happens during the MotionController.setup() call when MotionLayout is initializing.

Reproducible Code #

Layout File #

<androidx.constraintlayout.motion.widget.MotionLayout 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    app:layoutDescription="@xml/motion_scene">
    <com.spruce.messenger.composer.MessageTypeButton 
        android:id="@+id/messageType" 
        style="@style/messageTypeSelectionButton" 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:text="Message" />
</androidx.constraintlayout.motion.widget.MotionLayout>

MotionScene File #

<?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="100" 
        motion:motionInterpolator="linear">
        <OnSwipe 
            motion:dragDirection="dragRight" 
            motion:maxAcceleration="18" 
            motion:onTouchUp="autoComplete" 
            motion:touchAnchorId="@+id/messageType" 
            motion:touchAnchorSide="left" 
            motion:touchRegionId="@+id/messageType" />
    </Transition>
    <ConstraintSet android:id="@+id/start">
        <Constraint android:id="@+id/messageType">
            <CustomAttribute motion:attributeName="StrokeTintColor" motion:customColorValue="#D68739" />
            <CustomAttribute motion:attributeName="TextColor" motion:customColorValue="#2D70FF" />
            <CustomAttribute motion:attributeName="BackgroundTint" motion:customColorValue="#F1F6FF" />
        </Constraint>
    </ConstraintSet>
    <ConstraintSet android:id="@+id/end">
        <Constraint android:id="@id/messageType">
            <CustomAttribute motion:attributeName="StrokeTintColor" motion:customColorValue="#D68739" />
            <CustomAttribute motion:attributeName="TextColor" motion:customColorValue="#D68739" />
            <CustomAttribute motion:attributeName="BackgroundTint" motion:customColorValue="#FFFCF3" />
        </Constraint>
    </ConstraintSet>
</MotionScene>

Crash Log #

java.lang.ArrayIndexOutOfBoundsException: length=2; index=2
    at androidx.constraintlayout.motion.widget.MotionController.setup(MotionController.java:592)
    at androidx.constraintlayout.motion.widget.MotionLayout.setupMotionViews(MotionLayout.java:1196)
    at androidx.constraintlayout.motion.widget.MotionLayout.access$700(MotionLayout.java:820)
    at androidx.constraintlayout.motion.widget.MotionLayout$Model.reEvaluateState(MotionLayout.java:1850)
    at androidx.constraintlayout.motion.widget.MotionLayout.onMeasure(MotionLayout.java:1977)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:825)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:704)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at com.android.internal.policy.DecorView.onMeasure(DecorView.java:716)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2718)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1572)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1855)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
    at android.view.Choreographer.doCallbacks(Choreographer.java:761)
    at android.view.Choreographer.doFrame(Choreographer.java:696)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Update #

I've already filed this issue with the Android ConstraintLayout team for further investigation.

内容的提问来源于stack exchange，提问作者M-Wajeeh