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

Question

我在玩MotionLayout时遇到一个奇怪的问题

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)

进行一些调试，发现导致该崩溃的MotionLayout版本存在一些差异：

正如您在alpha-3中看到的那样，尝试获取运动场景持续时间this.mDevModeDraw.draw(canvas, this.mFrameArrayList, this.mScene.getDuration(), this.mDebugPath);时将调用this.mScene.getDuration()并导致崩溃，但是在alpha-2中，由于if条件不同，因此不会调用它。

我应该如何解决？

Answer 1

尽管您可以检查布局集上是否具有app:layoutDescription属性，但是您尚未发布XML。

Answer 2

对我来说，它发生在我继承MotionLayout并用<merge...标签夸大其内容的时候。忘记了合并标记的参数会被忽略，而您必须手动将其重新应用到代码中。

所以现在看起来像这样：

class SomeLayout : MotionLayout {

constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr) {
    inflate(context, R.layout.some_layout, this)
    loadLayoutDescription(R.xml.some_motion_scene)
    setTransition(R.id.start, R.id.end)
}

...

Answer 3

通过更新库修复了同一问题 来自

implementation 'androidx.constraintlayout:constraintlayout:2.0.1'

到

implementation 'androidx.constraintlayout:constraintlayout:2.0.4'

Answer 4

这次特定崩溃的根本原因是 AAPT 的一个变化，它发现了 a bug in ConstraintLayout's new attributes。这是在其中一个测试版中修复的，因此如果您现在进入 MotionLayout，您应该只使用最新的稳定版本。如果由于某种原因您停留在旧的 alpha 版本上，您可以将这些放在您的 values/attrs.xml 文件中以解决崩溃：

    <attr name="duration"/>
    <attr name="flow_horizontalSeparator"/>
    <attr name="flow_verticalSeparator"/>
    <attr name="motionPathRotate"/>
    <attr name="motionProgress"/>
    <attr name="waveDecay"/>

我强烈建议改用最新的稳定版本 2.0.4。