Sean Clark Hess Sean Clark Hess - 3 months ago 26
Objective-C Question

How can I click a button behind a transparent UIView?

Let's say we have a view controller with one sub view. the subview takes up the center of the screen with 100 px margins on all sides. We then add a bunch of little stuff to click on inside that subview. We are only using the subview to take advantage of the new frame ( x=0, y=0 inside the subview is actually 100,100 in the parent view).

Then, imagine that we have something behind the subview, like a menu. I want the user to be able to select any of the "little stuff" in the subview, but if there is nothing there, I want touches to pass through it (since the background is clear anyway) to the buttons behind it.

How can I do this? It looks like touchesBegan goes through, but buttons don't work.

Answer

Create a custom view for your container and override the pointInside: message to return NO when the point isn't within an eligible child view, like this:

@interface PassthroughView : UIView
@end

@implementation PassthroughView
-(BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event {
    for (UIView *view in self.subviews) {
        if (!view.hidden && view.alpha > 0 && view.userInteractionEnabled && [view pointInside:[self convertPoint:point toView:view] withEvent:event])
            return YES;
    }
    return NO;
}
@end

Using this view as a container will allow any of its children to receive touches but the view itself will be transparent to events.

Edit: Here is the Swift version

class PassThroughView: UIView {
    override func pointInside(point: CGPoint, withEvent event: UIEvent?) -> Bool {
        for subview in subviews {
            if !subview.hidden && subview.alpha > 0 && subview.userInteractionEnabled && subview.pointInside(convertPoint(point, toView: subview), withEvent: event) {
                return true
            }
        }
        return false
    }
}