我的Android应用程序有问题。有一个Custome适配器从我调用一个片段，其中有mediaPlayer播放音频文件。片段启动时，播放音频文件。如果用户按下ActionBar中的后退按钮，则不会出现任何问题，并切换到启动此片段的前一个片段。但是当用户再次按下后退按钮时，会发生错误＆＃34; MyApp停止工作＆＃34;。我试图通过断点在我的主要活动的onBackPressed方法上捕获问题，但在调用此方法之前出现错误。
我的自定义适配器中的代码调用音频片段：
android.support.v4.app.FragmentTransaction fragmentTransaction;
FragmentManager fragmentManager = ((AppCompatActivity) context).getSupportFragmentManager();
AudioFragment fragment = new AudioFragment();
fragment.SoundTitle = currentAV.getFileText();
fragment.oneTimeOnly = 0;
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.addToBackStack(null);
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
我的音频代码片段有媒体播放器：
public class AudioFragment extends Fragment {
private Button btnForward, btnPause, btnPlay, btnBackward;
private ImageButton btnStop;
private ImageView iv;
private MediaPlayer mediaPlayer;
private double startTime = 0;
private double finalTime = 0;
private Handler myHandler;
private int forwardTime = 90000;
private int backwardTime = 90000;
private SeekBar seekbar;
private TextView tx1,tx2,tx3, txTitle;
private boolean _isStopped = true;
private int _length = 0;
public static int oneTimeOnly = 0;
public static String SoundTitle = "";
public AudioFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_audio, container, false);
btnForward = (Button) view.findViewById(R.id.btnForward);
btnPause = (Button) view.findViewById(R.id.btnPause);
btnPlay = (Button)view.findViewById(R.id.btnPlay);
btnBackward = (Button)view.findViewById(R.id.btnBackward);
btnStop = (ImageButton)view.findViewById(R.id.btnStop);
iv=(ImageView)view.findViewById(R.id.imageView);
txTitle =(TextView)view.findViewById(R.id.textview);
txTitle.setText(SoundTitle);
tx1=(TextView)view.findViewById(R.id.textView2);
tx2=(TextView)view.findViewById(R.id.textView3);
tx3=(TextView)view.findViewById(R.id.textView4);
tx3.setText("");
myHandler = new Handler();
seekbar=(SeekBar)view.findViewById(R.id.seekBar);
((AppCompatActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);
Toolbar toolbar = (Toolbar) getActivity().findViewById(R.id.toolbar);
((AppCompatActivity)getActivity()).setSupportActionBar(toolbar);
toolbar.setNavigationIcon(R.drawable.abc_ic_ab_back_mtrl_am_alpha);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
getActivity().onBackPressed();
}
});
btnPlay.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(getActivity(), "Playing sound",Toast.LENGTH_SHORT).show();
PlaySound();
}
});
btnPause.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(getActivity(), "Pausing sound",Toast.LENGTH_SHORT).show();
mediaPlayer.pause();
_length = mediaPlayer.getCurrentPosition();
btnPause.setEnabled(false);
btnPlay.setEnabled(true);
}
});
btnForward.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int temp = (int)startTime;
if((temp+forwardTime)<=finalTime){
startTime = startTime + forwardTime;
mediaPlayer.seekTo((int) startTime);
//Toast.makeText(getActivity(),"You have Jumped forward 5 seconds",Toast.LENGTH_SHORT).show();
}
else{
Toast.makeText(getActivity(),"Cannot jump forward 60 seconds",Toast.LENGTH_SHORT).show();
}
}
});
btnBackward.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int temp = (int)startTime;
if((temp-backwardTime)>0){
startTime = startTime - backwardTime;
mediaPlayer.seekTo((int) startTime);
//Toast.makeText(getActivity(),"You have Jumped backward 5 seconds",Toast.LENGTH_SHORT).show();
}
else{
Toast.makeText(getActivity(),"Cannot jump backward 60 seconds",Toast.LENGTH_SHORT).show();
}
}
});
btnStop.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
btnPause.setEnabled(false);
btnPlay.setEnabled(true);
_isStopped = true;
_length = 0;
mediaPlayer.stop();
myHandler.removeCallbacks(UpdateSongTime);
mediaPlayer.release();
mediaPlayer=null;
}
});
PlaySound();
return view;
}
private Runnable UpdateSongTime = new Runnable() {
public void run() {
startTime = mediaPlayer.getCurrentPosition();
tx1.setText(String.format("%d min, %d sec",
TimeUnit.MILLISECONDS.toMinutes((long) startTime),
TimeUnit.MILLISECONDS.toSeconds((long) startTime) -
TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.
toMinutes((long) startTime)))
);
seekbar.setProgress((int)startTime);
myHandler.postDelayed(this, 100);
}
};
private void PlaySound(){
if(!_isStopped){
mediaPlayer.seekTo(_length);
mediaPlayer.start();
btnPause.setEnabled(true);
btnPlay.setEnabled(false);
return;
}
String sdpath = Environment.getExternalStorageDirectory().getAbsolutePath();
String avPath = "";
avPath = sdpath + Gen.AudioPath;
_isStopped = false;
mediaPlayer = MediaPlayer.create(getActivity(), Uri.parse(avPath));
seekbar.setClickable(false);
btnPause.setEnabled(false);
mediaPlayer.start();
finalTime = mediaPlayer.getDuration();
startTime = mediaPlayer.getCurrentPosition();
if (oneTimeOnly == 0) {
seekbar.setMax((int) finalTime);
oneTimeOnly = 1;
}
tx2.setText(String.format("%d min, %d sec",
TimeUnit.MILLISECONDS.toMinutes((long) finalTime),
TimeUnit.MILLISECONDS.toSeconds((long) finalTime) -
TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes((long) finalTime)))
);
tx1.setText(String.format("%d min, %d sec",
TimeUnit.MILLISECONDS.toMinutes((long) startTime),
TimeUnit.MILLISECONDS.toSeconds((long) startTime) -
TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes((long) startTime)))
);
seekbar.setProgress((int)startTime);
myHandler.postDelayed(UpdateSongTime,100);
btnPause.setEnabled(true);
btnPlay.setEnabled(false);
Gen.IsMediaPlayerRun = true;
}
}
如果有人有解决方案，请帮忙。感谢
编辑：以下是LOGCAT（最后一行）
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.khan.abc, PID: 21144
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.FragmentActivity.onBackPressed()' on a null object reference
at com.example.khan.abc.AudioFragment$1.onClick(AudioFragment.java:125)
at android.view.View.performClick(View.java:4848)
at android.view.View$PerformClick.run(View.java:20262)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5631)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
答案 0 :(得分：1)
此代码生成空指针...
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override public void onClick(View v) {
getActivity().onBackPressed();
}
});
添加空指针保护
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override public void onClick(View v) {
Activity parent = getActivity();
if(parent != null)
parent.onBackPressed();
}
});
但是，你的代码有点奇怪......
例如：您创建片段并为工具栏设置clickListener。然后，您返回到上一个片段..但是，您的工具栏仍在引用来自已杀死片段的侦听器...
我认为最好的方法是在父活动中处理工具栏......我不确定你是否可以......但我会改变它......
希望这可以提供帮助。