空对象引用上的 void android.view.View.dispatchWindowVisibilityChanged(int)'

Question

我有一个 Activity A [MainActivity]，我从它开始 Activity B [Videoplayer]
案例 1： 点击 Activity A 中的视频缩略图 => 转到 Activity B => 播放视频几秒钟（重要：您需要播放视频几秒钟）=> 单击返回导航 => 返回到活动 A => 没有崩溃。

案例 2： 点击活动 A 中的视频缩略图 => 转到活动 B => 缓冲区和视频开始播放 => 立即点击返回导航（重要：不要播放视频）= > 应用尝试返回 Activity A => 崩溃及其一致。

注意：我没有在 Activity A 的 onResume() 中编写代码，只是为了确保我没有覆盖任何可能导致崩溃的 onResume() 相关代码。 堆栈跟踪不指向应用程序代码中的一行，它只显示来自 android 源库的堆栈跟踪。我为此花费了超过 4+小时，感谢您的帮助。

Activity B [玩家活动] 代码：

public class VitamioPlayerActivity extends AppCompatActivity implements MediaPlayer.OnErrorListener, MediaPlayer.OnPreparedListener, MediaPlayer.OnTimedTextListener {
public static final String TAG = VitamioPlayerActivity.class.getSimpleName();

@Bind(R.id.videoView)
VideoView videoView;

@Bind(R.id.progressBar)
ProgressBar progressBar;

@Bind(R.id.subtitle_view)
TextView mSubtitleView;

private VideoModel videoModel;
private long mPosition = 0;

private boolean isLiveChannel;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_vitamio);
    ButterKnife.bind(this);
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);

    if (getIntent() == null)
        return;

    if (getIntent().getExtras() == null)
        return;

    if (!getIntent().getExtras().containsKey(AppConstant.KEY_BUNDLE_VIDEO))
        return;

    videoModel = (VideoModel) getIntent().getExtras().getSerializable(AppConstant.KEY_BUNDLE_VIDEO);
    if (videoModel == null)
        return;

    playVideo();
}


VideoControllerView controllerView;

void playVideo() {
    String path = null;
    if (videoModel.isLoadBalancer()) {
        path = URLHelper.getInstance().getPlayableVideoUrl(videoModel.getVideoUrl());
    } else
        path = videoModel.getVideoUrl();

    if (TextUtils.isEmpty(path)) {
        Toast.makeText(this, "Please edit MediaPlayer Activity, " + "and set the path variable to your media file path." + " Your media file must be stored on sdcard.", Toast.LENGTH_LONG).show();
        return;
    }
    isLiveChannel = !(path.contains(".mp4"));
    videoView.setVideoURI(Uri.parse(path));
    videoView.setMediaController(controllerView = new VideoControllerView(this, !isLiveChannel));
    videoView.requestFocus();
    videoView.start();

    videoView.setOnPreparedListener(this);
    videoView.setOnErrorListener(this);
}

@Override
public void onPrepared(MediaPlayer mediaPlayer) {
    mediaPlayer.setPlaybackSpeed(1.0f);
}

@Override
public void onTimedText(String text) {
    mSubtitleView.setText(text);
}

@Override
public void onTimedTextUpdate(byte[] pixels, int width, int height) {
    int a = 1;
}


@Nullable
@OnClick(R.id.imvHeaderBack)
void doBack() {
    finish();
}

@Override
public void onBackPressed() {
    finish();
}

@Override
protected void onPause() {
    mPosition = videoView.getCurrentPosition();
    videoView.stopPlayback();
    super.onPause();
}

@Override
protected void onResume() {
    if (mPosition > 0) {
        videoView.seekTo((int) mPosition);
        mPosition = 0;
    }
    super.onResume();
}

@Override
public boolean onError(MediaPlayer mp, int what, int extra) {
    WindowUtils.getInstance().genericInfoMsgWithOKCallBack(this, null, "Sorry, Cannot Play Video", R.color.redStatus,
            new ViewConstructor.InfoDisplayListener() {
                @Override
                public void onPositiveSelection(DialogInterface alertDialog) {
                    doBack();
                }
            });
    return true;
}

}

堆栈跟踪：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.dispatchWindowVisibilityChanged(int)' on a null object reference
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1310)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1410)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1134)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6050)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:860)
    at android.view.Choreographer.doCallbacks(Choreographer.java:672)
    at android.view.Choreographer.doFrame(Choreographer.java:608)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:846)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5442)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)

Answer 1

在检查了更多文档之后，您似乎从 onCreate 文档中陷入了这种情况：https://developer.android.com/reference/android/app/Activity.html#onCreate(android.os.Bundle)

您可以在此函数中调用 finish()，在这种情况下，onDestroy() 将立即被调用，而不会执行任何其余的 Activity 生命周期（onStart()、onResume()、onPause() 等）。

由于您的onBackPressed 和doBack 都调用finish()，您可能会遇到videoView 仍然在您的活动的onCreate 中开始的竞争条件，在onCreate 结束之前按下返回并且您的活动在尝试播放 videoView 时被破坏，同时跳过所有其他生命周期函数，导致这个奇怪的堆栈跟踪崩溃。

修复：覆盖 onResume 并在那里调用 videoView.start 并覆盖 onDestroy 和 onStop 并在那里调用 if (videoView.isPlaying()) videoView.stopPlayback