Work out UIView size

Question

I am trying to draw a chess board. In the code below I get the width of the board and divide it by 8 to get the size of the squares I need to draw as follows:

let squareLength = CGFloat(self.bounds.size.width / 8)
var x:CGFloat = 0
var y:CGFloat = 0

for rowIndex in 1...8 {

    // odd rows start indented
    if (rowIndex % 2 == 1) {
        x += squareLength
    }

    // draw this row
    for colIndex in 1...4 {
        let f:CGRect = CGRectMake(x, y, squareLength, squareLength)
        let square = BlackSquare(frame: f)
        addSubview(square)

        x += squareLength * 2
    }

    // reset
    x = 0
    y += squareLength
}

The problem I am having is that the squares are drawn at double their point size.

According to my understanding, both the value returned by self.bounds.size.width as well as the number passed to the frame I create are in points so surely they should match and the chessboard should draw correctly?

In other words how do I adjust to fix this?

Here is the drawing code, from Square.swift:

import Foundation
import UIKit

class BlackSquare: UIView {
    override init (frame : CGRect) {
        super.init(frame : frame)

        opaque = false
        backgroundColor = UIColor.clearColor()
    }

    required init(coder aDecoder: NSCoder) {
       super.init(coder: aDecoder)
    }

    override func drawRect(rect: CGRect) {
        let ctx = UIGraphicsGetCurrentContext()
        CGContextSetRGBStrokeColor(ctx, 0.5, 0.5, 0.5, 1.0)
        CGContextSetLineWidth(ctx, 0.75)

        let spacing = 4
        let numLines = Int(Int(rect.width) / spacing) * 2

        for index in 1...numLines {
            let m = CGFloat(index * spacing)
            let zero = CGFloat(0)

            CGContextMoveToPoint(ctx, m, zero)
            CGContextAddLineToPoint(ctx, zero, m)
            CGContextStrokePath(ctx)
        }
     }
}

Answer 1

OK I figured it out. In my code above, the function is called from init, in a view that uses autolayout before its constraints are resolved. The value coming back wasn't making sense.

I moved the call to layoutSubviews() and all the sizes and maths work out perfectly as expected.