I recently had to write a short chunk of code to determine when a user touches a specific rectangular region on the screen. Detecting this is nothing more than getting a reference to a CGPoint (x and y coordinates) of the location touched and checking to see if the point is within the rectangular bounds of interest.

The following example shows one approach, the workhorse is CGRectContainsPoint.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

/*---------------------------------------------------------------------------
* Touches began
*--------------------------------------------------------------------------*/
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{
  // Detect touch anywhere
  UITouch *touch = [touches anyObject];
 
  // Get the specific point that was touched
  CGPoint point = [touch locationInView:self.view]; 
  NSLog(@"pointx: %f pointy:%f", point.x, point.y);
 
  // See if the point touched is within these rectangular bounds
  if (CGRectContainsPoint(CGRectMake(5, 5, 40, 130), point))
  {
    do something...
  } 
}

I use CGRectMake to define the bounds of the rectangle and pass in the variable point that was obtained from the touch location.

As with CGRectContainsPoint, CGRectMake is a C function, which is defined as follows:

CGRect CGRectMake(CGFloat x, CGFloat y, CGFloat width, GFloat height);

The C structures you’ll need to put all the pieces together, are shown below:

struct CGRect 
{
   CGPoint origin;
   CGSize size;
};
 
struct CGPoint 
{
   CGFloat x;
   CGFloat y;
};
 
struct CGSize 
{
   CGFloat width;
   CGFloat height;
};

CGFloat is nothing more than a floating point number that is defined as a typedef, based on the system architecture. In other words, it’s just a float.

For more information about CGRect, CGSize and CGPoint, you can read this post.