通信問題

Question

我有，我想與服務器進行通信的fragmment，但問題是，我總是得到空指針

我有這個在我的片段onCreateView：

public class BrowseFragment extends Fragment implements View.OnClickListener{ 

private MusicService mMusicService; 


@Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment, container, false); 



    mMusicService = new MusicService(this); 
      mMusicService.setCallback(new MusicService.Callback() { 


           @Override 
           public void onPlayPause(String state) { 
            //Do something 
           } 
          }); 

} 
} 

這是我的服務：

public class MusicService extends MediaBrowserServiceCompat { 


public interface Callback { 
     public void onPlayPause(String state); 
    } 

    public void setCallback(Callback callback) { 
     this.mCallback = callback; 
    } 





private void PauseRequest() { 
     mPlayback.pause(); 
     //if (mCallback != null) { 
      mCallback.onPlayPause("PAUSE"); 
     //} 
} 

} 

I'm得到這個致命異常：主要

Process: com.geobytenet.mediaplayer, PID: 3262 
java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.android.mediabrowserservice.MusicService$Callback.onPlayPause(java.lang.String)' on a null object reference 

我希望你能幫助我

Answer 1

在MusicService開始，我在BrowseFragment添加了這個方法

public void pausePlay() { 
     PauseRequest(); 
    } 

然後，在onCreateView()

Button button = (Button)rootView.findViewById(R.id.button_play_pause); 
    button.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      mMusicService.pausePlay(); 
     } 
    }); 

Answer 2

你不能像簡單的類一樣在Android中創建MusicService。它是一種服務，它必須以正確的方式https://medium.com/google-developers/mediabrowserservicecompat-and-the-modern-media-playback-app-7959a5196d90