無法在onCreate中獲得歌曲持續時間，但可以通過按下按鈕獲得歌曲持續時間

我有一個自定義媒體服務和一個與之通信的音頻播放器類，但未綁定到該服務。無法在onCreate中獲得歌曲持續時間，但可以通過按下按鈕獲得歌曲持續時間

當我創建MyService的對象並編寫代碼時： - myService.player.getDuration() in onCreate我在此行上得到空指針異常。

但是，如果我在同一個屏幕上點擊某個按鈕監聽器來編寫此代碼，那麼我會得到確切的持續時間。

我已經嘗試過所有可能的語法來解決這個問題，但m仍然無法解決問題。

**我的服務的代碼是： - **

private static final String TAG = "MyService"; 
    public static MediaPlayer player; 
    String song_uri,url; 
    Bundle b; 
    private IBinder myBinder; 
    private boolean isplaying; 
    public static final String Song_uri="song_uri"; 
    public static final String EXTRA_SHUFFLE="EXTRA_SHUFFLE"; 

     @Override 
    public IBinder onBind(Intent intent) { 
     return null; 
    } 
    public class MyBinder extends Binder{ 
     MyService getService() 
     { 
      return MyService.this; 
     } 
    } 

    @Override 
    public void onCreate() { 
     Log.d(TAG, "onCreate "+song_uri); 
      } 


    @Override 
    public void onDestroy() { 
     //Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show(); 
     DataManager.getInstance().setWantsToPlaySong(false); 
     DataManager.getInstance().setCurrentPosition(0); 
     Log.d(TAG, "onDestroy"); 
     player.stop(); 
    //player.release(); 
    } 

public void onPause() 
{ 

player.pause(); 
} 

public double duration() 
{ 
return player.getDuration();  
} 

    public void onStart(Intent intent, int startid) { 
     DataManager.getInstance().setWantsToPlaySong(true); 
    Bundle b=intent.getExtras(); 
    song_uri=b.getString("song_uri"); 
    Uri path=Uri.parse(song_uri); 


    player = MediaPlayer.create(this,path); 
    player.setLooping(false); // Set looping 
    //Toast.makeText(this, "My Service Started"+" Duration = "+(player.getDuration()/1000)/60, Toast.LENGTH_SHORT).show(); 
     Log.d(TAG, "onStart"+song_uri); 
     player.start(); 
    }

音頻播放器的代碼是： -

uri = this.getIntent().getExtras().getString("song_uri"); 
     buttonStart = (Button) findViewById(R.id.buttonStart); 
     buttonStop = (Button) findViewById(R.id.buttonStop); 
     buttonPause = (Button) findViewById(R.id.buttonPause); 
     tracks = dbManager.getAllSongs(AudioPlayer2.this); 

     buttonForward = (Button) findViewById(R.id.buttonforward); 
     buttonBackward = (Button) findViewById(R.id.buttonbackward); 
     //========================================================================================= 
     sArtworkUri = Uri.parse("content://media/external/audio/albumart"); 
      //myservice=new MyService(); 

     Uri path = Uri.parse(uri); 
     current_song=this.getIntent().getExtras().getInt("current_song"); 
     albumArtUri = this.getIntent().getExtras().getString("album_art"); 
     Uri sArtworkUri = Uri.parse("content://media/external/audio/albumart"); 
     album_id = Long.parseLong(this.getIntent().getStringExtra("album_id")); 
     int id = Integer.parseInt(this.getIntent().getStringExtra("album_id")); 

     albumImageUri = ContentUris.withAppendedId(sArtworkUri, album_id); 
     ivAlbumArt = (ImageView) findViewById(R.id.album_art); 

     songName = this.getIntent().getStringExtra("song_name"); 
     albumName = this.getIntent().getStringExtra("album_name"); 

     tvName = (TextView) findViewById(R.id.tv_name); 
     tvAlbum = (TextView) findViewById(R.id.tv_album); 
     if (songName != null) { 
      tvName.setText(songName); 
     } 

     if (albumName != null) { 
      tvAlbum.setText(albumName); 
     } 

    // buttonStart.performClick(); 

     if (DataManager.getInstance().getOnPausedSong()=="y"){ 
      //Toast.makeText(AudioPlayer2.this, "stage 1", Toast.LENGTH_SHORT).show(); 
      if(DataManager.getInstance().getPausedSongName()==songName){ 
       //Toast.makeText(AudioPlayer2.this, "stage 1", Toast.LENGTH_SHORT).show(); 
      buttonStart.setVisibility(View.GONE); 
      buttonPause.setVisibility(View.VISIBLE); 
     } 
     } 
     FetchImage fetchImage = new FetchImage(); 
     fetchImage.execute(); 

      /*if(DataManager.getInstance().getSong_uri()!=null) 
      { 
       stopService(new Intent(this, MyService.class)); 
      }*/ 
    // if(myService.player.isPlaying()) 
     //{ 
     stopService(new Intent(this, MyService.class)); 
     Intent intent = new Intent(this,MyService.class); 
      Bundle b = new Bundle(); 
      b.putString("song_uri",uri); 
      intent.putExtras(b); 
      startService(intent); 
      myService.player.setOnCompletionListener(new OnCompletionListener() { 

       @Override 
       public void onCompletion(MediaPlayer mp) { 
        // TODO Auto-generated method stub 
        buttonStart.setVisibility(View.VISIBLE); 
        buttonPause.setVisibility(View.GONE); 
       } 
      }); 
      buttonStart.setVisibility(View.GONE); 
      buttonPause.setVisibility(View.VISIBLE); 

      // Toast.makeText(this, "Duration: "+myService.player.getDuration(), Toast.LENGTH_LONG).show(); 
     /*//}//DataManager.getInstance().setSong_uri(uri); 
     Intent intent = new Intent(this,MyService.class); 
     Bundle b = new Bundle(); 
     b.putString("song_uri",uri); 
     intent.putExtras(b); 
     startService(intent); 
     buttonStart.setVisibility(View.GONE); 
     buttonPause.setVisibility(View.VISIBLE); 
     DataManager.getInstance().setSong_uri(uri); 
     DataManager.getInstance().setOnPausedSong("y"); 
     DataManager.getInstance().setPausedSongName(songName); 
     */ //buttonStart.setPressed(true); 

     //======================================================================================= 
     buttonStart.setOnClickListener(this); 
     buttonPause.setOnClickListener(this); 
     buttonForward.setOnClickListener(this); 
     buttonBackward.setOnClickListener(this); 
     buttonStop.setOnClickListener(this); 
     // buttonPause.performClick(); 
/*  new Thread(myThread).start(); 

*/ } 

     // Thread for seekbar 


     // song starts playing 

     public void onClick(View src) { 
     switch (src.getId()) { 
     case R.id.buttonStart: 
      if(DataManager.getInstance().getSongPause()=="y"){ 
       myService.player.start(); 
       DataManager.getInstance().setSongPause("n"); 
       buttonStart.setVisibility(View.GONE); 
       buttonPause.setVisibility(View.VISIBLE); 
      // DataManager.getInstance().setWantsToPlaySong(true); 
       //DataManager.getInstance().setOnPausedSong("n"); 
       //DataManager.getInstance().setOnPausedSong("y"); 
      }else{ 
     stopService(new Intent(this, MyService.class)); 
      DataManager.getInstance().setSong_uri(uri); 
      Intent intent = new Intent(this,MyService.class); 
      Bundle b = new Bundle(); 
      b.putString("song_uri",uri); 
      intent.putExtras(b); 
      startService(intent); 
      buttonStart.setVisibility(View.GONE); 
      buttonPause.setVisibility(View.VISIBLE); 
      DataManager.getInstance().setOnPausedSong("y"); 
      DataManager.getInstance().setPausedSongName(songName); 
      } 
      //Toast.makeText(this, "My Service Started", Toast.LENGTH_LONG).show(); 
      break; 
     case R.id.buttonStop: 
      Log.d(TAG, "onClick: stopping srvice"); 
      stopService(new Intent(this, MyService.class)); 
      buttonStart.setVisibility(View.VISIBLE); 
      buttonPause.setVisibility(View.GONE); 
    break; 
     case R.id.buttonforward: 
      stopService(new Intent(this, MyService.class)); 
      current_song++; 
      FetchAllMusic fetchAllMusic = new FetchAllMusic(); 
      fetchAllMusic.execute(); 
      //new Thread(myThread).start(); 


       break; 
     case R.id.buttonbackward: 
       Log.d(TAG, "onClick: stopping service"); 
       stopService(new Intent(this, MyService.class)); 
       if(current_song>0){ 
       current_song--; 
       } 
       FetchAllMusic fetchAllMusic2 = new FetchAllMusic(); 
       fetchAllMusic2.execute(); 

       break; 
     case R.id.buttonPause: 
       buttonStart.setVisibility(View.VISIBLE); 
       buttonPause.setVisibility(View.GONE); 
      /* MyService myservice=new MyService(); 
      myservice.onPause();*/ 
       myService.player.pause(); 
       DataManager.getInstance().setSongPause("y"); 
       DataManager.getInstance().setWantsToPlaySong(false); 
       DataManager.getInstance().setOnPausedSong("n"); 
       DataManager.getInstance().setPausedSongName(songName); 
       //duration=myService.player.getDuration(); 

      // Toast.makeText(this, ""+duration, Toast.LENGTH_LONG).show(); 

     } 
     } 
     public void onBackPressed() { 
      try { 
        //addvideo.removeView(DBManager.getInstance().getVideo()); 
       DataManager.getInstance().setSong_uri(uri); 
      DataManager.getInstance().setAlbum_id(""+album_id); 
      DataManager.getInstance().setAlbumName(albumName); 
      DataManager.getInstance().setSongName(songName); 
      DataManager.getInstance().setAlbumArtUri(albumArtUri); 
      DataManager.getInstance().setCurrent_song(current_song); 
      DataManager.getInstance().setWantsToPlaySong(false); 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
      super.onBackPressed(); 
     } 

      private Runnable myThread = new Runnable(){ 

       @Override 
       public void run() { 
         Log.d(TAG, "Thread Starts"); 
       // TODO Auto-generated method stub 
       while (myProgress<100){ 
       try{ 
         Log.d(TAG, "Thread Starts"); 
         myHandle.sendMessage(myHandle.obtainMessage()); 
       Thread.sleep(3000); 
       } 
       catch(Throwable t){ 
       } 
       } 
       } 

       Handler myHandle = new Handler(){ 

       public void handleMessage(Message msg) { 
       // TODO Auto-generated method stub 
       myProgress++; 
       seekbar.setProgress(myProgress); 
       } 
       }; 
       };

來源

2011-03-18 abhishek

這不是一個語法問題;這是一個可變的初始化問題。 myService或myService.player爲null，當該行在onCreate()中執行時。檢查你的代碼是否在初始化這些代碼，並確保你沒有在它們被設置之前引用它們。

來源

2011-03-18 08:23:15

我應該在哪裏初始化代碼？我已經完成了我可能已經在我的應用程序中的每個活動擴展到的baseScreen中初始化它的所有內容。 myService.player不能爲null，因爲歌曲正在播放，myService不能爲null，因爲它是在baseScreen類中初始化的變量 – abhishek 2011-03-18 08:33:05

現在我寫了這個代碼myService = new MyService（）; Tolar.makeText（AudioPlayer2.this，「」+ myService.player.getDuration（），Toast.LENGTH_SHORT）.show（）;甚至這是給我nullPointer異常...請幫助 – abhishek 2011-03-18 08:45:19

MyService（）構造函數是否爲'player'賦值？如果不行，那就是你的問題。（如你所說，如果代碼在一個onClick監聽器中工作，我懷疑'player'會在你的代碼執行中稍後分配。 – 2011-03-18 15:41:40

無法在onCreate中獲得歌曲持續時間，但可以通過按下按鈕獲得歌曲持續時間

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