无法使用AnimatedVectorDrawable对FAB绘制进行动画处理

我正在尝试使FAB drawable动画，但会引发此错误。错误发生在我呼叫。start（）的行上。无法使用AnimatedVectorDrawable对FAB绘制进行动画处理

--------- beginning of crash 
04-25 14:40:09.169 25611-25611/com.test.testingfabanimation E/AndroidRuntime: FATAL EXCEPTION: main 
                         Process: com.test.testingfabanimation, PID: 25611 
                         java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference 
                          at android.graphics.drawable.AnimatedVectorDrawable$VectorDrawableAnimatorRT.createRTAnimator(AnimatedVectorDrawable.java:1262) 
                          at android.graphics.drawable.AnimatedVectorDrawable$VectorDrawableAnimatorRT.parseAnimatorSet(AnimatedVectorDrawable.java:1220) 
                          at android.graphics.drawable.AnimatedVectorDrawable$VectorDrawableAnimatorRT.init(AnimatedVectorDrawable.java:1187) 
                          at android.graphics.drawable.AnimatedVectorDrawable.ensureAnimatorSet(AnimatedVectorDrawable.java:851) 
                          at android.graphics.drawable.AnimatedVectorDrawable.start(AnimatedVectorDrawable.java:834) 
                          at com.test.testingfabanimation.MainActivity$1.onPageSelected(MainActivity.java:41) 
                          at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1967) 
                          at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:685) 
                          at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:669) 
                          at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2284) 
                          at android.view.View.dispatchTouchEvent(View.java:10024) 
                          at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2626) 
                          at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2307) 
                          at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632) 
                          at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321) 
                          at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632) 
                          at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321) 
                          at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632) 
                          at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321) 
                          at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632) 
                          at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321) 
                          at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632) 
                          at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321) 
                          at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632) 
                          at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321) 
                          at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:413) 
                          at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1809) 
                          at android.app.Activity.dispatchTouchEvent(Activity.java:3061) 
                          at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:71) 
                          at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:375) 
                          at android.view.View.dispatchPointerEvent(View.java:10244) 
                          at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4438) 
                          at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4306) 
                          at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3853) 
                          at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3906) 
                          at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3872) 
                          at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3999) 
                          at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3880) 
                          at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4056) 
                          at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3853) 
                          at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3906) 
                          at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3872) 
                          at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3880) 
                          at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3853) 
                          at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6246) 
                          at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6220) 
                          at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6181) 
04-25 14:40:09.171 25611-25611/com.test.testingfabanimation E/AndroidRuntime:  at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6349) 
                          at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) 
                          at android.os.MessageQueue.nativePollOnce(Native Method) 
                          at android.os.MessageQueue.next(MessageQueue.java:323) 
                          at android.os.Looper.loop(Looper.java:136) 
                          at android.app.ActivityThread.main(ActivityThread.java:6169) 
                          at java.lang.reflect.Method.invoke(Native Method) 
                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888) 
                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)

这是MainActivity在那里我试图动画FAB的代码。

viewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() { 
      @Override 
      public void onPageSelected(int position) { 
       switch (position) { 
        case 0: 
         fab.setImageResource(R.drawable.animate_forward); 
         break; 
        case 1: 
         fab.setImageResource(R.drawable.animate_backward); 
         break; 
       } 
       Drawable drawable = fab.getDrawable(); 
       if (drawable instanceof AnimatedVectorDrawable) 
        ((AnimatedVectorDrawable) drawable).start(); 
      } 
     });

我已经使用Roman Nurik的Android图标动画制作了动画制作的自定义绘图。

<animated-vector xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:aapt="http://schemas.android.com/aapt"> 
    <aapt:attr name="android:drawable"> 
     <vector 
      android:width="24dp" 
      android:height="24dp" 
      android:viewportWidth="24" 
      android:viewportHeight="24" 
      android:alpha="1"> 
      <path 
       android:name="foo" 
       android:pathData="@string/forward" 
       android:strokeColor="#000000" 
       android:strokeWidth="2" 
       android:strokeLineCap="round"/> 
     </vector> 
    </aapt:attr> 
    <target android:name="path_morph"> 
     <aapt:attr name="android:animation"> 
      <objectAnimator 
       android:name="foo" 
       android:propertyName="pathData" 
       android:duration="300" 
       android:valueFrom="@string/forward" 
       android:valueTo="@string/backward" 
       android:valueType="pathType" 
       android:interpolator="@android:anim/accelerate_decelerate_interpolator"/> 
     </aapt:attr> 
    </target> 
</animated-vector>

animate_forward和animate_backword xmls类似。只有路径中的字符串值互换。

这是我第一次使用AnimatedVectorDrawables。有什么我失踪？所有的教程都会在网络上显示相同的代码。

来源

2017-04-25 Aakaash Jois