How do I make UILabel display outlined text?

I was able to do it by overriding drawTextInRect:

- (void)drawTextInRect:(CGRect)rect {

  CGSize shadowOffset = self.shadowOffset;
  UIColor *textColor = self.textColor;

  CGContextRef c = UIGraphicsGetCurrentContext();
  CGContextSetLineWidth(c, 1);
  CGContextSetLineJoin(c, kCGLineJoinRound);

  CGContextSetTextDrawingMode(c, kCGTextStroke);
  self.textColor = [UIColor whiteColor];
  [super drawTextInRect:rect];

  CGContextSetTextDrawingMode(c, kCGTextFill);
  self.textColor = textColor;
  self.shadowOffset = CGSizeMake(0, 0);
  [super drawTextInRect:rect];

  self.shadowOffset = shadowOffset;

}

A simpler solution is to use an Attributed String like so:

Swift 4:

let strokeTextAttributes: [NSAttributedStringKey : Any] = [
    NSAttributedStringKey.strokeColor : UIColor.black,
    NSAttributedStringKey.foregroundColor : UIColor.white,
    NSAttributedStringKey.strokeWidth : -2.0,
    ]

myLabel.attributedText = NSAttributedString(string: "Foo", attributes: strokeTextAttributes)

Swift 4.2:

let strokeTextAttributes: [NSAttributedString.Key : Any] = [
    .strokeColor : UIColor.black,
    .foregroundColor : UIColor.white,
    .strokeWidth : -2.0,
    ]

myLabel.attributedText = NSAttributedString(string: "Foo", attributes: strokeTextAttributes)

On a UITextField you can set the defaultTextAttributes and the attributedPlaceholder as well.

Note that the NSStrokeWidthAttributeName has to be negative in this case, i.e. only the inner outlines work.

After reading the accepted answer and the two corrections to it and the answer from Axel Guilmin, I decided to compile an overall solution in Swift, that suits me:

import UIKit

class UIOutlinedLabel: UILabel {

    var outlineWidth: CGFloat = 1
    var outlineColor: UIColor = UIColor.whiteColor()

    override func drawTextInRect(rect: CGRect) {

        let strokeTextAttributes = [
            NSStrokeColorAttributeName : outlineColor,
            NSStrokeWidthAttributeName : -1 * outlineWidth,
        ]

        self.attributedText = NSAttributedString(string: self.text ?? "", attributes: strokeTextAttributes)
        super.drawTextInRect(rect)
    }
}

You can add this custom UILabel class to an existing label in the Interface Builder and change the thickness of the border and its color by adding User Defined Runtime Attributes like this:

Result:

There is one issue with the answer's implementation. Drawing a text with stroke has a slightly different character glyph width than drawing a text without stroke, which can produce "uncentered" results. It can be fixed by adding an invisible stroke around the fill text.

Replace:

CGContextSetTextDrawingMode(c, kCGTextFill);
self.textColor = textColor;
self.shadowOffset = CGSizeMake(0, 0);
[super drawTextInRect:rect];

with:

CGContextSetTextDrawingMode(context, kCGTextFillStroke);
self.textColor = textColor;
[[UIColor clearColor] setStroke]; // invisible stroke
self.shadowOffset = CGSizeMake(0, 0);
[super drawTextInRect:rect];

I'm not 100% sure, if that's the real deal, because I don't know if self.textColor = textColor; has the same effect as [textColor setFill], but it should work.

Disclosure: I'm the developer of THLabel.

I've released a UILabel subclass a while ago, which allows an outline in text and other effects. You can find it here: https://github.com/tobihagemann/THLabel