Drawing multiple circles on a single line CGGraphicsContext - swift

Question

I have a custom class that manages a custom view that has a horizontal center on screen (which will represent a solid line). And I've drawn the line like this:
override func drawRect(rect: CGRect)
{
let line = UIGraphicsGetCurrentContext()
CGContextSetLineWidth(line, 3.0)
CGContextSetStrokeColorWithColor(line, UIColor.redColor().CGColor)
CGContextMoveToPoint(line, 0, self.bounds.midY)
CGContextAddLineToPoint(line, self.bounds.width, self.bounds.midY)
CGContextStrokePath(line)
}
However, I need to draw a multiple solid circles on this line and try to look it like a point in a chart. I'm trying to make a mini chart representation in fact. How can I draw the circles? With a nested 'for in' loop or? Is there any official chart API from Apple?

Answer 1

UIGraphicsGetCurrentContext() gives you a context that you can draw multiple things into. Calling it line is not the right idea, because it can contain multiple lines, or circles, or all sorts of other things.
Think of the context as an artist sitting in front of a blank canvas. You give the artist instructions, like "draw a red line, then draw a blue circle". The artist follows the instructions, and afterwards, you look at the canvas.
Here's how you might draw a line and then a circle.
let context = UIGraphicsGetCurrentContext()
// Tell the context what stroked paths should look like
CGContextSetLineWidth(context, 3.0)
CGContextSetStrokeColorWithColor(context, UIColor.redColor().CGColor)
// Draw a single line
CGContextMoveToPoint(context, 0, self.bounds.midY)
CGContextAddLineToPoint(context, self.bounds.width, self.bounds.midY)
CGContextStrokePath(context)
// Now draw a circle by filling a path.
// First, set the fill color:
CGContextSetFillColorWithColor(context, UIColor.blueColor().CGColor)
// Specify how big the circle is, and where its center is:
let circleRadius = CGFloat(5.0)
let circleCenter = CGPoint(x: self.bounds.midX, y: self.bounds.midY)
// Then add a circle to the context, by specifying the rectangle that surrounds it:
let circleRect = CGRect(x: circleCenter.x - circleRadius,
y: circleCenter.y - circleRadius,
width: circleRadius * 2,
height: circleRadius * 2)
CGContextAddEllipseInRect(context, circleRect)
// And fill that circle:
CGContextFillPath(context)
If you want to draw more circles but in different places, just call CGContextAddEllipseInRect and CGContextFillPath again, but with different values for circleRect. Depending on what you want, a for loop might be appropriate. It's entirely up to you.
If you don't want to write it yourself, there are lots of 3rd-party chart libraries available, just do a search. Apple does not provide an "official" one.