已知宽高，在某区域获取随机的中心center，或者区域 rect

• 中心

// 获取随机中心位置，在某个视图不超出某个区域的情况下

    static func randomCenterWith(in rect:CGRect, w:CGFloat, h:CGFloat) -> CGPoint {
        let sW = rect.size.width
        let sH = rect.size.height
        let minX = w/2
        let maxX = sW - w/2
        let randomX = CGFloat(arc4random_uniform(UInt32(maxX - minX))) + minX
        let minY = h/2
        let maxY = sH - h/2
        let randomY = CGFloat(arc4random_uniform(UInt32(maxY - minY))) + minY
        let randomCenter = CGPoint(x: randomX, y: randomY)
        return randomCenter
    }

• 区域

    static func randomRectWiht(in rect:CGRect, w:CGFloat, h:CGFloat) -> CGRect {
        let randomCenter = self.randomCenterWith(in:rect, w: w, h: h)
        let rect = CGRect(x: randomCenter.x + w/2, y: randomCenter.y + h/2, width: w, height: h)
        return rect
    }