iPhone Development -CGPoint & NSTimer help

i want to jump balls in a specific field in the view, the problem i开发者_运维知识库s that i don't know how to define the positions of this field area and movement. also here is the code that i use to move the ball in the entire view (the ball object is a uiimageview on the view). thanks.

-(void) onTimer { ball.center = CGPointMake(ball.center.x+pos.x,ball.center.y+pos.y);

if(ball.center.x > 320 || ball.center.x < 0)
    pos.x = -pos.x;
if(ball.center.y > 460 || ball.center.y < 0)
    pos.y = -pos.y;

}

// Implement viewDidLoad to do additional setup after loading the view. - (void)viewDidLoad { pos = CGPointMake(14.0,7.0);

[NSTimer scheduledTimerWithTimeInterval:0.03 target:self selector:@selector(onTimer) userInfo:nil repeats:YES];

}

---

Instead of hard-coding 320 and 460, you can use the bounds of the view to get the are in which your balls should move.

Check out the bounds property of UIView.

---

@implementation ViewController {
    BOOL isPositiveXAxis;
    BOOL isPositiveYAxis;
}


- (void)viewDidLoad {
    [super viewDidLoad];

    //By default we are setting both BOOL value to YES because ballImage have (0,0) origin by default 
    isPositiveXAxis = YES;
    isPositiveYAxis = YES;
    imgBallView.layer.cornerRadius = imgBallView.frame.size.width/2;

    [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(animateBall) userInfo:nil repeats:YES];
}

-(void)animateBall {

        //getting current image transform, and we will modify it later in code
        CGAffineTransform transform = imgBallView.transform;


        //checking if ‘isPositiveXAxis is true and imgBallView xAxis have less value then view border
        if (isPositiveXAxis && imgBallView.frame.origin.x < self.view.frame.size.width - imgBallView.frame.size.width) {
            transform.tx++;
        }
        else {
            isPositiveXAxis = NO;

            if (transform.tx>0) {
                transform.tx--;
            }
            else {
                isPositiveXAxis = YES;
            }
        }

        //checking if ‘isPositiveYAxis is true and imgBallView yAxis have less value then view border
        if (isPositiveYAxis && imgBallView.frame.origin.y < self.view.frame.size.height - imgBallView.frame.size.height) {
            transform.ty++;
        }
        else {
            isPositiveYAxis = NO;

            if (transform.ty>0) {
                transform.ty--;
            }
            else {
                isPositiveYAxis = YES;
            }
        }

        //setting updated trasform to imgBallView it will look animated.
        imgBallView.transform =  transform;
}

The above code will generate the required pattern. It can be seen in the video: https://vid.me/G3zO, which may help you understand it better