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

我也遇到了同样的问题。这段代码为整个分段控件设置字体大小。类似的方法也可以用于设置字体类型。注意，这只适用于iOS5+

Obj C:

UIFont *font = [UIFont boldSystemFontOfSize:12.0f];
NSDictionary *attributes = [NSDictionary dictionaryWithObject:font
                                                       forKey:NSFontAttributeName];
[segmentedControl setTitleTextAttributes:attributes 
                                forState:UIControlStateNormal];

编辑:UITextAttributeFont已弃用-使用NSFontAttributeName代替。

编辑#2:对于Swift 4 NSFontAttributeName已更改为NSAttributedStringKey.font。

斯威夫特5:

let font = UIFont.systemFont(ofSize: 16)
segmentedControl.setTitleTextAttributes([NSAttributedString.Key.font: font], for: .normal)

斯威夫特4:

let font = UIFont.systemFont(ofSize: 16)
segmentedControl.setTitleTextAttributes([NSAttributedStringKey.font: font],
                                        for: .normal)

斯威夫特3:

let font = UIFont.systemFont(ofSize: 16)
segmentedControl.setTitleTextAttributes([NSFontAttributeName: font],
                                        for: .normal)

斯威夫特2.2:

let font = UIFont.systemFontOfSize(16)
segmentedControl.setTitleTextAttributes([NSFontAttributeName: font], 
    forState: UIControlState.Normal)

多亏了@audrey-gordeev的Swift实现

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)
    }
 }

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;

斯威夫特4

let font = UIFont.systemFont(ofSize: 16)
UISegmentedControl.setTitleTextAttributes([NSFontAttributeName: font], for: .normal)

C# / Xamarin：

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