You can set label's border via its underlying CALayer property:
#import <QuartzCore/QuartzCore.h>
myLabel.layer.borderColor = [UIColor greenColor].CGColor
myLabel.layer.borderWidth = 3.0
Swift 5:
myLabel.layer.borderColor = UIColor.darkGray.cgColor
myLabel.layer.borderWidth = 3.0
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…