how to get a subview of UIScrollView using a CGPoint - ios

Question

I have a UIScrollView with a number of rectangular subviews lined up, of equal sizes. Then I need to be able to pass a CGPoint to that UIScrollView and I want it to give me the rectangular subview that contains the CGPoint. That's basically hitTest:event, except hitTest:event: doesn't work with UIScrollView once CGPoint goes beyond the UIScrollView bounds and doesn't look into its actual content.
What's everyone been doing about this? How to "hit test" on a UIScrollView content view?
Here's some code to illustrate the problem:
NSArray *rectangles = [self getBeautifulRectangles];
CGFloat rectangleLength;
rectangleLength = 100;
// add some rectangle subviews
for (int i = 0; i < rectangles.count; i++) {
UIView *rectangle = [rectangles objectAtIndex:i];
[rectangle setFrame:CGRectMake(i * rectangleLength, 0, rectangleLength, rectangleLength)];
[_scrollView addSubview:rectangle];
}
[_scrollView setContentSize:CGSizeMake(rectangleLength * rectangles.count, rectangleLength)];
// add scroll view to parent view
UIView *containerView = [[UIView alloc] initWithFrame:CGRectMake(0,0,320, rectangleLength)];
[containerView addSubview:_scrollView];
// compute CGPoint to center of first rectangle
CGPoint number1RectanglePoint = CGPointMake(0 * rectangleLength + 50, 50);
// compute CGPoint to center of fifth rectangle
CGPoint number5RectanglePoint = CGPointMake(4 * rectangleLength + 50, 50);
UIView *firstSubview = [containerView hitTest:number1RectanglePoint withEvent:nil];
UIView *fifthSubview = [containerView hitTest:number5RectanglePoint withEvent:nil];
if (firstSubview) NSLog(#"first rectangle OK");
if (fifthSubview) NSLog(#"fifth rectangle OK");
output: first rectangle OK

Answer 1

You should be able to loop through the scrollview subviews
+(UIView *)touchedViewIn:(UIScrollView *)scrollView atPoint:(CGPoint)touchPoint {
CGPoint actualPoint = CGPointMake(touchPoint.x + scrollView.contentOffset.x, scrollView.contentOffset.y + touchPoint.y);
for (UIView * subView in scrollView.subviews) {
if(CGRectContainsPoint(subView.frame, actualPoint)) {
NSLog(#"THIS IS THE ONE");
return subView;
}
}
//Nothing touched
return nil;
}

Answer 2

I guess you pass the wrong CGPoint coordinate to the hitTest:withEvent: method causing wrong behavior if the scroll view is scrolled.
The coordinate you pass to this method must be in the target views coordinate system. I guess your coordinate is in the UIScrollView's superview's coordinate system.
You can convert the coordinate prior to using it for the hit test using CGPoint hitPoint = [scrollView convertPoint:yourPoint fromView:scrollView.superview].
In your example you let the container view perform the hit testing, but the container can only see & hit the visible portion of the scroll view and thus your hit fails.
In order to hit subviews of the scroll view which are outside of the visible area you have to perform the hit test on the scroll view directly:
UIView *firstSubview = [_scrollView hitTest:number1RectanglePoint withEvent:nil];
UIView *fifthSubview = [_scrollView hitTest:number5RectanglePoint withEvent:nil];