swift 自动计算字符串的宽和高

这里我是给String写了一个类扩展

 import Foundation
 import UIKit

extension String{

func sizeWithText(font: UIFont, size: CGSize) -> CGSize {
    let attributes = [NSAttributedStringKey.font: font]
    let option = NSStringDrawingOptions.usesLineFragmentOrigin
    let rect:CGRect = self.boundingRect(with: size, options: option, attributes: attributes, context: nil)
        return rect.size;
    }

}

调用时候 直接用字符串调用即可