Android的java矩形陣列不起作用

Question

我想做一個小迷宮遊戲。爲此，我現在有4面牆可以打出一個球。全部是ImageViews。我利用了Rect.intersect方法。

爲了從牆壁上獲得矩形，我使用了ImageView.getHitRect。矩形然後被存儲在矩形數組中。這似乎都是失敗的地方。當我使用一個矩形的這個陣列getHitRect我得到以下錯誤的方法：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.graphics.Rect.set(int, int, int, int)' on a null object reference 

這裏是我的代碼

private ImageView ball; 
private ImageView wall[] = new ImageView[4]; 
private TextView text; 
private SensorManager sManager; 
private int a=300;  //x position 
private int b=300;  //y position 
int x=0; 
int y=0; 


Rect rect[] = new Rect[4]; 
Rect ballrect = new Rect(); 

float show = 1; 



boolean allowedMovement[]={true,true,true,true}; 

int maxX=0; 
int maxY=0; 


@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    ball = (ImageView) findViewById(R.id.ball); 
    text = (TextView) findViewById(R.id.info); 
    wall[0] = (ImageView) findViewById(R.id.wall1); 
    wall[1] = (ImageView) findViewById(R.id.wall2); 
    wall[2] = (ImageView) findViewById(R.id.wall3); 
    wall[3] = (ImageView) findViewById(R.id.wall4); 
    sManager = (SensorManager) getSystemService(SENSOR_SERVICE); 


} 

//when this Activity starts 
@Override 
protected void onResume() 
{ 
    super.onResume(); 
    /*register the sensor listener to listen to the gyroscope sensor, use the 
    callbacks defined in this class, and gather the sensor information as quick 
    as possible*/ 
    sManager.registerListener(this, sManager.getDefaultSensor(Sensor.TYPE_ORIENTATION), SensorManager.SENSOR_DELAY_FASTEST); 
} 

//When this Activity isn't visible anymore 
@Override 
protected void onStop() 
{ 
    //unregister the sensor listener 
    sManager.unregisterListener(this); 
    super.onStop(); 
} 

@Override 
public void onAccuracyChanged(Sensor arg0, int arg1) 
{ 
    //Do nothing. 
} 

public void move(int x, int y) { 
    RelativeLayout.LayoutParams alp = (RelativeLayout.LayoutParams) ball.getLayoutParams(); 
    int maxMovementX=Math.abs(x); 
    int maxMovenentY=Math.abs(y); 
    int stepsTakenX=0; 
    int stepsTakenY=0; 

    while(maxMovementX>stepsTakenX || maxMovenentY>stepsTakenY) { 
     hitCheck(); 
     //up 0, down 1, right 2, left 3 
     if (stepsTakenX < maxMovementX) { 
      stepsTakenX=stepsTakenX+1; 
      if (x > 0 && allowedMovement[2] == true) {//right 
       a = a - 1; 
      } 
      if (x < 0 && allowedMovement[3] == true) {//left 
       a = a + 1; 
      } 
     } 

     if (stepsTakenY < maxMovenentY) { 
      stepsTakenY=stepsTakenY+1; 
      if (y > 0 && allowedMovement[1] == true) {//down 
       b = b - 1; 
      } 
      if (y < 0 && allowedMovement[0] == true) {//up 
       b = b + 1; 
      } 
     } 
     alp.leftMargin = a; 
     alp.topMargin = b; 
     ball.setLayoutParams(alp); 
    } 
} 

public void hitCheck(){ 
    //up 0, down 1, right 2, left 3 
    for(int i=0;i<4;i++){ 
     allowedMovement[i]=true; 
    } 
    ball.getHitRect(ballrect); 

    for(int i=0;i<4;i++) { 
     wall[i].getHitRect(rect[i]); 

     if (Rect.intersects(rect[i], ballrect)) { 
      wall[i].setAlpha(show); 
      float wy = (ballrect.width() + rect[i].width()) * (ballrect.centerY() - rect[i].centerY()); 
      float hx = (ballrect.height() + rect[i].height()) * (ballrect.centerX() - rect[i].centerX()); 

      if (wy > hx) { 
       if (wy > -hx) {//top 
        allowedMovement[1] = false; 
       } else {//left 
        allowedMovement[2] = false; 
       } 
      } else { 
       if (wy > -hx) {//right 
        allowedMovement[3] = false; 
       } else {//bottom 
        allowedMovement[0] = false; 
       } 
      } 
     } 

    } 
} 

它有沒有問題與ballrect但與實體不在陣列中

Answer 1

Rect rect[] = new Rect[4];只分配存儲對象引用的位置，不分配實際對象。

嘗試插入rect[i] = new Rect();前wall[i].getHitRect(rect[i]);