如何在iOS Swift / Obj-C中编写自适应/动态UILabel？

I tried drawing it with CGRectMake + adjustsFontSizeToFitWidth, it gets it to work but only until if I need to size my UILabel less than 'default system font size' (i.e. 16 maybe), it doesn't get bigger more than 'default system font size'. On the other hand, if I hard code that font size like I tried drawing it with CGRectMake + adjustsFon