好的，所以我在同一个活动中有两个音轨，因此他们正在使用两个媒体播放器。我把一切都搞好了。唯一的问题是在调用onPause（）时，当活动暂停时音频轨道会暂停。
如果正在播放音轨1，则暂停应用程序崩溃，因为mediaPlayer2导致空指针异常，而正在播放音轨2时则相反。
这里是Activity.java的代码
@Override
protected void onPause() {
super.onPause();
if (mediaPlayer1.isPlaying()) {
mediaPlayer1.pause();
pp1.setImageResource(R.drawable.play);
}
if (mediaPlayer2.isPlaying()) {
mediaPlayer2.pause();
pp2.setImageResource(R.drawable.play);
}
}
错误
错误1
java.lang.RuntimeException: Unable to pause activity {com.music.track/com.music.track.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.media.MediaPlayer.isPlaying()' on a null object reference
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3454)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3408)
at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3383)
at android.app.ActivityThread.access$1100(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1391)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:152)
at android.app.ActivityThread.main(ActivityThread.java:5497)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.media.MediaPlayer.isPlaying()' on a null object reference
at com.music.track.MainActivity.onPause(MainActivity.java:186)
at android.app.Activity.performPause(Activity.java:6397)
at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1380)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3435)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3408)
at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3383)
at android.app.ActivityThread.access$1100(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1391)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:152)
at android.app.ActivityThread.main(ActivityThread.java:5497)
错误2
java.lang.RuntimeException: Unable to pause activity {com.music.test/com.music.test.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.media.MediaPlayer.isPlaying()' on a null object reference
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3454)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3408)
at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3383)
at android.app.ActivityThread.access$1100(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1391)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:152)
at android.app.ActivityThread.main(ActivityThread.java:5497)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.media.MediaPlayer.isPlaying()' on a null object reference
at com.music.test.MainActivity.onPause(MainActivity.java:181)
at android.app.Activity.performPause(Activity.java:6397)
at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1380)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3435)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3408)
at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3383)
at android.app.ActivityThread.access$1100(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1391)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:152)
at android.app.ActivityThread.main(ActivityThread.java:5497)
答案 0 :(得分：1)
检查mediaPlayer1＆amp; 2在使用之前为null