尝试使用 ExoPlayer 初始化流时出现 NullPointerException？

Posted 2023-03-07

【中文标题】尝试使用 ExoPlayer 初始化流时出现 NullPointerException？

【英文标题】：Getting a NullPointerException when trying to initialize streaming using ExoPlayer?

【发布时间】：2016-11-09 18:44:06

【问题描述】：

我正在开发的应用程序使用通用媒体播放器或 Nex Player 播放其视频文件。我的任务是让它使用我一直在努力实施的 Google ExoPlayer。但是，由于作为 exoplayer2 包的一部分的 Util 类中发生 NullPointerException，我无法初始化 ExoPlayer 类。

下面的方法已经在我的代码中实现了，用来初始化native player和nexplayer。

private void onLaunchStreamingSuccess() 
    final Context context = MediaDetailsStageButtons.this.getContext();
    final Intent intent = new Intent(context, ExoStreamingPlaybackScreen.class);
    intent.putExtra( AbstractMediaDetailsScreen.EXTRA_MEDIA_ID, MediaDetailsStageButtons.this.mMedia.getID() );
    context.startActivity(intent);

调用 startActivity 后，应用程序崩溃并显示以下日志语句

11-09 11:45:10.163 27482 27482 E QewErrorReporter: Entered uncaughtException [caught Exception: Unable to instantiate activity ComponentInfocom.directv.application.android.go.production/com.morega.qew.ui.streaming.ExoStreamingPlaybackScreen: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.PackageManager android.content.Context.getPackageManager()' on a null object reference]
11-09 11:45:10.163 27482 27482 E QewErrorReporter: java.lang.RuntimeException: Unable to instantiate activity ComponentInfocom.directv.application.android.go.production/com.morega.qew.ui.streaming.ExoStreamingPlaybackScreen: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.PackageManager android.content.Context.getPackageManager()' on a null object reference
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3096)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3352)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.app.ActivityThread.access$1100(ActivityThread.java:223)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1797)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.os.Handler.dispatchMessage(Handler.java:102)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.os.Looper.loop(Looper.java:158)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.app.ActivityThread.main(ActivityThread.java:7231)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at java.lang.reflect.Method.invoke(Native Method)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
11-09 11:45:10.163 27482 27482 E QewErrorReporter: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.PackageManager android.content.Context.getPackageManager()' on a null object reference
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.content.ContextWrapper.getPackageManager(ContextWrapper.java:97)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at com.google.android.exoplayer2.util.Util.getUserAgent(Util.java:676)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at com.morega.qew.ui.streaming.ExoStreamingPlaybackScreen.<init>(ExoStreamingPlaybackScreen.java:88)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at java.lang.Class.newInstance(Native Method)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3086)
11-09 11:45:10.163 27482 27482 E QewErrorReporter:  ... 9 more

进入 Util 类，方法“getUserAgent”是问题发生的地方，特别是在 try 块的第二行。

public static String getUserAgent(Context context, String applicationName) 
String versionName;
try 
  String packageName = context.getPackageName();
  PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);
  versionName = info.versionName;
 catch (NameNotFoundException e) 
  versionName = "?";

return applicationName + "/" + versionName + " (Linux;Android " + Build.VERSION.RELEASE
    + ") " + "ExoPlayerLib/" + ExoPlayerLibraryInfo.VERSION;

这可能只是我对 Android 的缺乏经验，这就是我无法解决此问题的原因，但我希望能得到一些帮助来解决这个问题。

【参考方案1】：

line 88 中的ExoStreamingPlaybackScreen.java 正在拨打什么电话？看起来这就是崩溃发生的地方。

你传入的Context可能是null。

【讨论】：

该行是'private String userAgent = Util.getUserAgent(this, "");'但它是在初始字段声明中。我现在对其进行了更改，以便在 onCreate 中对其进行初始化，这似乎已经解决了这个问题。非常感谢，下次发问题之前我会更加努力。