碰撞检测（小球与舞台以及挡板碰撞的判断）

package view
{
/**
 * @author zoe
 *
 */
import flash.display.Sprite;
import flash.events.Event;

public class GameScene extends Sprite
{
    private var rect:MoveRect;
    private var ball:Ball;
    
    private var speedX:int;
    private var speedY:int;
    private var r:int;
    public function GameScene()
    {
        init();
    }
    
    private function init():void
    {
        rect = new MoveRect();
        ball = new Ball();
        addChild(rect);
        addChild(ball)
        
        rect.y = 560;
        ball.x = 300;
        ball.y = 300;
        
        speedX = 5;
        speedY = 5;
        r = ball.width/2;    
        
    }
    
    public function useEfHandler():void
    {
        addEventListener(Event.ENTER_FRAME,efHandler);
    }
    
    private function efHandler(event:Event):void
    {
        rect.x = mouseX - rect.width/2;        
        
        ball.x += speedX;
        ball.y += speedY;
        
        if(ball.x < r)
        {
            speedX = -speedX;
        }
        
        if(ball.x >= this.stage.stageWidth - r)
        {
            speedX = -speedX;
        }
        
        if(ball.y < r)
        {
            speedY = -speedY;
            trace(speedY);
        }
        
        if(ball.y >= this.stage.stageHeight - r)
        {
            speedY = -speedY;
        }
//之所以全用if，没有else，是因为如果写成if，else if，else if，有一种情况符合走进去后就会完全跳出，当小球位置在四个角，例如同时符合ball.x < r和ball.y < r，就只会走进一种情况然后跳出方法，为了解决这个bug就全写成if。

isHit(); 
}
 private function isHit():void 
{ if(ball.hitTestObject(rect))
 {
 // speedX = -speedX;因为碰到下面的挡板X坐标不需要取反的，只有y要变动 
    speedY = -speedY; 
 }
 } 
} 
}