C# / Xamarin：

segment.SetTitleTextAttributes(new UITextAttributes { 
    Font = UIFont.SystemFontOfSize(font_size) }, UIControlState.Normal);

另一种选择是对控件应用转换。然而，它将缩小一切，包括控制边界。

segmentedControl.transform = CGAffineTransformMakeScale(.6f, .6f);

UISegmentedControl的扩展，用于设置字体大小。

extension UISegmentedControl {
    @available(iOS 8.2, *)
    func setFontSize(fontSize: CGFloat) {
            let normalTextAttributes: [NSObject : AnyObject]!
            if #available(iOS 9.0, *) {
                normalTextAttributes = [
                    NSFontAttributeName: UIFont.monospacedDigitSystemFontOfSize(fontSize, weight: UIFontWeightRegular)
                ]
            } else {
                normalTextAttributes = [
                    NSFontAttributeName: UIFont.systemFontOfSize(fontSize, weight: UIFontWeightRegular)
                ]
            }

        self.setTitleTextAttributes(normalTextAttributes, forState: .Normal)
    }
 }

斯威夫特风格:

UISegmentedControl.appearance().setTitleTextAttributes(NSDictionary(objects: [UIFont.systemFontOfSize(14.0)], forKeys: [NSFontAttributeName]), forState: UIControlState.Normal)

 UISegmentedControl.appearance().setTitleTextAttributes(NSDictionary(objects: [UIFont.systemFont(ofSize: 16.0)],
                                                                        forKeys: [kCTFontAttributeName as! NSCopying]) as? [AnyHashable : Any],
                                                           for: UIControlState.normal)

C# / Xamarin：

segment.SetTitleTextAttributes(new UITextAttributes { 
    Font = UIFont.SystemFontOfSize(font_size) }, UIControlState.Normal);