在 Swift 3 中,π 提供了 Float,Double 与 CGFloat 三种形式(Float.pi、Double.pi、CGFloat.pi),所以求周长还可以这么写:
let r = 3.0
let circumference = 2 * Double.pi * r
//我们还可以将前缀省略,让其通过类型自动推断
let r = 3.0
let circumference = 2 * .pi * r
let queue = dispatch_queue_create("Swift 2.2", nil)
dispatch_async(queue) {
print("Swift 2.2 queue")
}
let queue = DispatchQueue(label: "Swift 3")
queue.async {
print("Swift 3 queue")
}
class View: UIView {
override func drawRect(rect: CGRect) {
let context = UIGraphicsGetCurrentContext()
let blue = UIColor.blueColor().CGColor
CGContextSetFillColorWithColor(context, blue)
let red = UIColor.redColor().CGColor
CGContextSetStrokeColorWithColor(context, red)
CGContextSetLineWidth(context, 10)
CGContextAddRect(context, frame)
CGContextDrawPath(context, .FillStroke)
}
}let frame = CGRect(x: 0, y: 0, width: 100, height: 50)
let aView = View(frame: frame)
class View: UIView {
override func draw(_ rect: CGRect) {
guard let context = UIGraphicsGetCurrentContext() else {
return
}
let blue = UIColor.blue.cgColor
context.setFillColor(blue)
let red = UIColor.red.cgColor
context.setStrokeColor(red)
context.setLineWidth(10)
context.addRect(frame)
context.drawPath(using: .fillStroke)
}
}let frame = CGRect(x: 0, y: 0, width: 100, height: 50)
let aView = View(frame: frame)