XCode 8.1, Swift 3

import UIKit
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        UISegmentedControl.appearance().setTitleTextAttributes(NSDictionary(objects: [UIFont.systemFont(ofSize: 24.0)], 
        forKeys: [NSFontAttributeName as NSCopying]) as? [AnyHashable : Any], 
        for: UIControlState.normal)
    }
}

只需要改变数值(ofSize: 24.0)

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);

丹尼尔指给我正确的路。我是这样用的-

float scaleFactor = 0.8f;

UISegmentedControl *segmentedControl = [[UISegmentedControl alloc]
initWithFrame:CGRectMake(10, 70, 300/scaleFactor,35)];

[segmentedControl insertSegmentWithTitle:@"..." atIndex:0 animated:NO];
[segmentedControl insertSegmentWithTitle:@"..." atIndex:1 animated:NO];
[segmentedControl insertSegmentWithTitle:@"..." atIndex:2 animated:NO];

segmentedControl.transform = CGAffineTransformMakeScale(scaleFactor, 1);
CGPoint segmentedControlCenter = segmentedControl.center;
segmentedControlCenter.x = self.center.x;
segmentedControl.center = segmentedControlCenter;

你可以通过递归检查从UISegmentedControl开始的每个视图来获得UILabel的实际字体。我不知道这是不是最好的方法，但它确实有效。

@interface tmpSegmentedControlTextViewController : UIViewController {
}

@property (nonatomic, assign) IBOutlet UISegmentedControl * theControl;

@end

@implementation tmpSegmentedControlTextViewController

@synthesize theControl; // UISegmentedControl

- (void)viewDidLoad {
  [self printControl:[self theControl]];
  [super viewDidLoad];
}

- (void) printControl:(UIView *) view {
  NSArray * views = [view subviews];
  NSInteger idx,idxMax;
  for (idx = 0, idxMax = views.count; idx < idxMax; idx++) {
    UIView * thisView = [views objectAtIndex:idx];
    UILabel * tmpLabel = (UILabel *) thisView;
    if ([tmpLabel respondsToSelector:@selector(text)]) {
      NSLog(@"TEXT for view %d: %@",idx,tmpLabel.text);
      [tmpLabel setTextColor:[UIColor blackColor]];
    }

    if (thisView.subviews.count) {
      NSLog(@"View has subviews");
      [self printControl:thisView];
    }
  }
}

@end

在上面的代码中，我只是设置了UILabel的文本颜色，但你也可以获取或设置字体属性。

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

XCode 8.1, Swift 3

import UIKit
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        UISegmentedControl.appearance().setTitleTextAttributes(NSDictionary(objects: [UIFont.systemFont(ofSize: 24.0)], 
        forKeys: [NSFontAttributeName as NSCopying]) as? [AnyHashable : Any], 
        for: UIControlState.normal)
    }
}

只需要改变数值(ofSize: 24.0)