ios - What's the correct way to put a line under a UITextField -

i want have borderless uitextfield underneath have 1 or 2 pixel high guide line underlines field. clear, don't want text inside uitextfield underlined, field, whether it's empty or full of text.

an example seen in example of google material design:

so of course stick in uiimage shows solid color , fit space, doesn't seem quite elegant, there better way that's more "correct" , future-proof if i'm worrying how code work several generations of ios down line , on knows devices?

p.s. rather scratch using obj-c find library.

i did yesterday... subclass uitextfield , work.

note: cleaner though use textfielddidbeginediting: , textfielddidendediting: changing of line height , color, either through nsnotificationcenter or delegate methods.

- (void)setup  {     self.hairlinelayer = [calayer layer];     self.hairlinelayer.backgroundcolor = [uicolor materialtextdarkdividercolor].cgcolor;     [self.layer addsublayer:self.hairlinelayer]; }  - (void)layoutsubviews {     [super layoutsubviews];      cgfloat hairlineheight = 0;     if (self.isfirstresponder) {         self.hairlinelayer.backgroundcolor = [uicolor redcolor].cgcolor;         hairlineheight = 1.4;     } else {         self.hairlinelayer.backgroundcolor = [uicolor graycolor].cgcolor;         hairlineheight = 1/[uiscreen mainscreen].scale;     }      self.hairlinelayer.frame = cgrectmake(0, cgrectgetheight(self.bounds) - hairlineheight, cgrectgetwidth(self.bounds), hairlineheight); }