iOS: how to move ball - ios

Question

Hi how do i create a moving ball on iOS.
When the program starts, I will display the ball on the left of the screen. Subsequently, each time i click a UIButton, how do i move the ball to the right on the same x-axis.
I managed to display the ball but how do i update and redraw its location when the UIButton is pressed? currently each time i press the UIButton, it creates a new ball and the old balls are not cleared.
i understand its because i recreate a new instance of the ball. So how shall i go about fixing this?
Here is my code....
ballView.m
#implementation BallView
-(id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
[self setBackgroundColor:[UIColor clearColor]];
}
return self;
}
-(void)drawRect:(CGRect)dirtyRect
{
NSLog(#"in drawRect");
// Get the graphics context and clear it
CGContextRef ctx = UIGraphicsGetCurrentContext();
// Draw a solid ball
CGContextSetRGBFillColor(ctx, 0, 0, 0, 1);
CGContextFillEllipseInRect(ctx, dirtyRect);
[self setNeedsDisplay];
}
-(BOOL)canBecomeFirstResponder
{
return YES;
}
MoveBallController.m
-(void)moveBall
{
CGRect viewFrame = CGRectMake(0, 0, 30, 30);
BallView *ball = [[BallView alloc] initWithFrame:viewFrame];
[[self dotView] addSubview:ball];
}

Answer 1

Create one BallView instance and store it in an instance variable. Then when the button is clicked you simply update the ball's frame:
- (void)viewDidLoad {
[super viewDidLoad];
CGRect viewFrame = CGRectMake(0, 0, 30, 30);
_ball = [[BallView alloc] initWithFrame:viewFrame];
[[self dotView] addSubview:_ball];
}
- (void)moveBall {
CGRect frame = _ball.frame;
frame.origin.x += 5; // use some appropriate increment
_ball.frame = frame;
}
where _ball is your new instance variable.