Boundary for draggable image ios - ios

Question

I'm trying to create a draggable image, but i'm trying to confine it's dragging to within a small square rather than the full screen. Could someone tell me where i'm going wrong?. I've placed the code that I have so far below:
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [[event allTouches] anyObject];
if([touch view] == dot) {
CGPoint location = [touch locationInView:self.view];
dot.center = location;
if (location.x >10) {
location.x =10;
} else if (location.x <10) {
location.x = 10;
}
if (location.y >20) {
location.y =20;
} else if (location.y < 20) {
location.y = 20;
}
}
}

Answer 1

You are assigning location before you are making changes to it.
Apply your limits to location first then assign it to dot.
Also, your limits you are showing would lock your position to 10,20 since you are not allowing it to be more than 10 or less than 10. Likewise with 20.
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [[event allTouches] anyObject];
if([touch view] == dot) {
CGPoint location = [touch locationInView:self.view];
location.x = MIN(MAX(location.x, 0),10);
location.y = MIN(MAX(location.y, 0),20);
dot.center = location;
}
}

Answer 2

I have implemented an image dragging function recently like this. I use the PAN Gesture to move the image which results in two CGFloats "endPointX and endPointY". In the code below between the comments "Stay on Screen Check" and "End Stay on Screen check", I check if these are on the screen. If not I adjust them to prevent the image moving off the screen.
I hope that helps. If you want to move the image within a small part of the total screen then I would add the image to a holder subview and then check the holder view .bounds.size.width/height above instead.
CGFloat endPointX = translatedPoint.x + (.35*[(UIPanGestureRecognizer*)sender
velocityInView:self.view].x);
CGFloat endPointY = translatedPoint.y + (.35*[(UIPanGestureRecognizer*)sender velocityInView:self.view].y);
// Stay on the screen check
if(endPointX < 0) {
endPointX = 0;
} else if(endPointX > self.view.bounds.size.width) {
endPointX = self.view.bounds.size.width;
}
if(endPointY < 0) {
endPointY = 0;
} else if(endPointY > self.view.bounds.size.height) {
endPointY = self.view.bounds.size.height;
}
// End of the Stay on Screen check
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:.35];
[UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
[[sender view] setCenter:CGPointMake(endPointX, endPointY)];
[UIView commitAnimations];