NullPointerException en utilisant SurfaceView

Question

Je veux créer l'application de démonstration avec SurfaceView. Mais a reçu le NullPointerException d'erreur dans une ligne "GameThread = gameView.getThread();" voici mon extrait complet du Code

MainActivity:

public class MainActivity extends Activity { 

GameView gameView; 
TutorialThread GameThread; 
Button btnStart, btnStop; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    Log.d("OnCreate -", "I am in onCreate method.."); 
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
      WindowManager.LayoutParams.FLAG_FULLSCREEN); 

    requestWindowFeature(Window.FEATURE_NO_TITLE); 

    // get handles to the GameView from XML and the Tutorial thread. 
    gameView = (GameView) findViewById(R.id.gameView); 

    //Log.d("OnCreate -", ""+gameView.TAG); 

    GameThread = gameView.getThread(); 

    //GameThread.start(); 
    ClickListener clickListener = new ClickListener(); 

    // look up the happy shiny button 
    btnStart = (Button) findViewById(R.id.btnStart); 
    btnStart.setOnClickListener(clickListener); 

    btnStop = (Button) findViewById(R.id.btnStop); 
    btnStop.setOnClickListener(clickListener); 

    setContentView(R.layout.activity_main); 
} 

    class ClickListener implements View.OnClickListener { 

    @Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 

     switch (v.getId()) { 

     case R.id.btnStart: 
      /* 
      * if (GameThread.mState == GameThread.STATE_PLAY) { 
      * GameThread.setGameState(TutorialThread.STATE_RUNNING); 
      * 
      * } 
      */ 
      makeToast("This is Start Button"); 
      break; 

     case R.id.btnStop: 
      /* 
      * if (GameThread.mState == GameThread.STATE_RUNNING) { // 
      * GameThread.setGameState(TutorialThread.STATE_PLAY); } 
      */ 
      makeToast("This is Stop Button"); 
      break; 

     } 

    } 

    private void makeToast(String string) { 
     // TODO Auto-generated method stub 
     Toast.makeText(MainActivity.this, string,  Toast.LENGTH_LONG).show(); 
    } 

} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.activity_main, menu); 
    return true; 
} 

} 

et la classe Gameview est aussi: -

public class GameView extends SurfaceView implements SurfaceHolder.Callback { 

String TAG = "GameView"; 
private TutorialThread _thread; 

public GameView(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    // TODO Auto-generated constructor stub 
    getHolder().addCallback(this); 
    _thread = new TutorialThread(getHolder(), context); 
    setFocusable(true); 
} 

public TutorialThread getThread() { 
    return _thread; 
} 

@Override 
public void surfaceChanged(SurfaceHolder holder, int format, int width, 
     int height) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void surfaceCreated(SurfaceHolder holder) { 
    // TODO Auto-generated method stub 
    _thread.setRunning(true); 
    _thread.start(); 
} 

@Override 
public void surfaceDestroyed(SurfaceHolder holder) { 
    // TODO Auto-generated method stub 

    // we have to tell thread to shut down & wait for it to finish, or else 
    // it might touch the Surface after we return and explode 
    boolean retry = true; 
    _thread.setRunning(false); 
    while (retry) { 
     try { 
      _thread.join(); 
      retry = false; 
     } catch (InterruptedException e) { 
      // we will try it again and again... 
     } 
    } 
    } 

    } 

    class TutorialThread extends Thread { 
String TAG = "TutorialThread"; 
private SurfaceHolder _surfaceHolder; 
private boolean _run = false; 
Bitmap bitmapDroid; 

/** 
* State-tracking constants. 
*/ 

public static final int STATE_PLAY = 0; 
public static final int STATE_RUNNING = 1; 
public int mState = STATE_PLAY; 

Resources mRes; 

/** Handle to the application context, used to e.g. fetch Drawables. */ 
private Context mContext; 

float droidx = 200, droidy = 200; 

public TutorialThread(SurfaceHolder surfaceHolder, Context context) { 
    _surfaceHolder = surfaceHolder; 
    mContext = context; 
    mRes = context.getResources(); 
    // create droid and load bitmap 
    bitmapDroid = BitmapFactory 
      .decodeResource(mRes, R.drawable.ic_launcher); 

} 

public void setRunning(boolean run) { 
    _run = run; 
} 

@Override 
public void run() { 
    Canvas c; 
    while (_run) { 
     c = null; 
     try { 
      c = _surfaceHolder.lockCanvas(null); 
      synchronized (_surfaceHolder) { 
       onDraw(c); 
      } 
     } finally { 
      // do this in a finally so that if an exception is thrown 
      // during the above, we don't leave the Surface in an 
      // inconsistent state 
      if (c != null) { 
       _surfaceHolder.unlockCanvasAndPost(c); 
      } 
     } 
    } 
} 

public void onDraw(Canvas canvas) { 

    canvas.drawColor(Color.rgb(187, 255, 255)); 
    canvas.drawBitmap(bitmapDroid, droidx - (bitmapDroid.getWidth()/2), 
      droidy - (bitmapDroid.getHeight()/2), null); 

} 

    } 

déclaration de mise en page est:

<com.example.surfaceviewdemo.GameView 
    android:id="@+id/gameView" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:layout_weight="1" /> 

Answer 1

Vous devez d'abord définir la vue de votre contenu, puis seulement obtenir vos vues à partir de la mise en page. Par conséquent,

setContentView(R.layout.activity_main);

devrait être présent au-dessus de votre

gameView = (GameView) findViewById(R.id.gameView);