Bouncing Ball计划希望球重新出现在顶部并再次下降

Question

现在我的程序中球在Y轴上上下跳动。我想要的是球只能向下移动。当它到达屏幕的底部时，我希望它重新出现在顶部并再次开始。不断从上到下移动。

@implementation BounceViewController
@synthesize ball;

-(void) bounce{

    ball.center = CGPointMake(ball.center.x+position.x, ball.center.y+position.y); {

        if(ball.center.y>450 ||ball.center.y <0)
            position.y = -position.y; }
}

- (void)viewDidLoad {
    position = CGPointMake(0, 10);

    [NSTimer scheduledTimerWithTimeInterval:.05 target:self selector:@selector(bounce) userInfo:nil repeats:YES];
    [super viewDidLoad];
}
- (void)viewDidUnload
{
        [self setBall:nil];
        [super viewDidUnload];
}


@end

Answer 1

你的反弹方法中的

替换了行

if(ball.center.y>450 ||ball.center.y <0)
            position.y = -position.y;

与

if(ball.center.y>450 ||ball.center.y <0)
      ball.center = CGPointMake(ball.center.x+position.x, position.y);