从 alpha-2 迁移到 alpha-3 时，Android MotionLayout 崩溃

Question

我在玩 MotionLayout 时遇到了一个奇怪的问题

当我将使用的库版本从 com.android.support.constraint:constraint-layout:2.0.0-alpha2 更改为 com.android.support.constraint:constraint-layout: 2.0.0-alpha3

我的应用程序崩溃了:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: ru.sergik.collapsibleexoplayer, PID: 1376
java.lang.NullPointerException: Attempt to invoke virtual method 'int androidx.constraintlayout.motion.widget.MotionScene.getDuration()' on a null object reference
    at androidx.constraintlayout.motion.widget.MotionLayout.dispatchDraw(MotionLayout.java:1634)
    at android.view.View.updateDisplayListIfDirty(View.java:19306)
    at android.view.View.draw(View.java:20093)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4421)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4207)
    at androidx.constraintlayout.widget.ConstraintLayout.dispatchDraw(ConstraintLayout.java:2072)
    at android.view.View.updateDisplayListIfDirty(View.java:19306)
    at android.view.View.draw(View.java:20093)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4421)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4207)
    at android.view.View.updateDisplayListIfDirty(View.java:19306)
    at android.view.View.draw(View.java:20093)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4421)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4207)
    at android.view.View.updateDisplayListIfDirty(View.java:19306)
    at android.view.View.draw(View.java:20093)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4421)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4207)
    at android.view.View.updateDisplayListIfDirty(View.java:19306)
    at android.view.View.draw(View.java:20093)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4421)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4207)
    at android.view.View.updateDisplayListIfDirty(View.java:19306)
    at android.view.View.draw(View.java:20093)
    at android.view.ViewGroup.drawChild(ViewGroup.java:4421)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4207)
    at android.view.View.draw(View.java:20373)
    at com.android.internal.policy.DecorView.draw(DecorView.java:980)
    at android.view.View.updateDisplayListIfDirty(View.java:19315)
    at android.view.ThreadedRenderer.updateViewTreeDisplayList(ThreadedRenderer.java:686)
    at android.view.ThreadedRenderer.updateRootDisplayList(ThreadedRenderer.java:692)
    at android.view.ThreadedRenderer.draw(ThreadedRenderer.java:800)
    at android.view.ViewRootImpl.draw(ViewRootImpl.java:3496)
    at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:3283)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2818)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1780)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7827)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
    at android.view.Choreographer.doCallbacks(Choreographer.java:723)
    at android.view.Choreographer.doFrame(Choreographer.java:658)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
    at android.os.Handler.handleCallback(Handler.java:789)
    at android.os.Handler.dispatchMessage(Handler.java:98)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6944)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

在进行一些调试时，我发现导致此崩溃的 MotionLayout 版本存在一些差异:

正如您在 alpha-3 中看到的那样 this.mDevModeDraw.draw(canvas, this.mFrameArrayList, this.mScene.getDuration(), this.mDebugPath); 将被调用并导致崩溃试图获取运动场景持续时间 this.mScene.getDuration()，但在 alpha-2 中，由于不同的 if 条件，它不会被调用。

我该如何解决？

Answer 1

虽然您可以检查布局集上是否有 app:layoutDescription 属性，但您还没有发布 XML。