获取 UINavigationBar Title Font

for (UIView * view in self.navigationController.navigationBar.subviews) {
    for (UIView * view2 in view.subviews) {
        if ([view2 isKindOfClass:[UILabel class]]) {
            UILabel * label = (UILabel *)view2;
            _titleLabelFont = label.font;
        }
    }
}