弧在圆上的位置

Question

I've got few pixels wide circle (circle is UIBezierPath based). I have to put an arc (which is basically UIView subclass with custom drawing) on the circle so the arc covers circle. I know how to calculate rotation of arc and position but something is not right. I mean I know the reason - it's beacause center property which is assigned to center of UIView, if it was center of the arc, everything would be great. But it's not.

I also know how to solve that. I have to calculate smaller radius where I will put arcs on. But how to do that. Basically it seems easy but because of the arc is in rectangular UIView it gets a bit harder. I'll show you some images so you can see the problem.

Answer 1

The easiest way to do this is to change the anchor point of each arc view's layer. You can read about the anchor point here if you don't already know about it. You will need to add the QuartzCore framework to your build target and add #import <QuartzCore/QuartzCore.h> .

CGRect circleBounds = circleView.bounds;

topArcView.layer.anchorPoint = CGPointMake(.5, 0);
topArcView.layer.position = CGPointMake(CGRectGetMidX(circleBounds), 0);

bottomArcView.layer.anchorPoint = CGPointMake(.5, 1);
bottomArcView.layer.position = CGPointMake(CGRectGetMidX(circleBounds), CGRectGetMaxY(circleBounds));

leftArcView.layer.anchorPoint = CGPointMake(0, .5);
leftArcView.layer.position = CGPointMake(circleBounds.origin.x, CGRectGetMidY(circleBounds));

rightArcView.layer.anchorPoint = CGPointMake(1, .5);
rightArcView.layer.position = CGPointMake(CGRectGetMaxX(circleBounds), CGRectGetMidY(circleBounds));

Answer 2

Perhaps you could make the UIView subclass the same size and center point as the circle's rect. Then draw the arc in the correct location.