查看iOS视图层级并修改UIsearchBar的cancel按钮不失去作用

(lldb) po [self.searchBar recursiveDescription]
<UISearchBar: 0x7ff35854f370; frame = ( ;  ); text = 'p'; opaque = NO; gestureRecognizers = <NSArray: 0x7ff358550380>; layer = <CALayer: 0x7ff35854f890>>
   | <UIView: 0x7ff35854fb90; frame = ( ;  ); clipsToBounds = YES; autoresize = W+H; layer = <CALayer: 0x7ff35854fd00>>
   |    | <UISearchBarBackground: 0x7ff3585504d0; frame = ( ;  ); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x7ff358550950>>
   |    | <UISearchBarTextField: 0x7ff358551480; frame = ( ;  ); text = 'p'; clipsToBounds = YES; opaque = NO; gestureRecognizers = <NSArray: 0x7ff358553e80>; layer = <CALayer: 0x7ff358551850>>
   |    |    | <_UISearchBarSearchFieldBackgroundView: 0x7ff358785900; frame = ( ;  ); opaque = NO; autoresize = W+H; userInteractionEnabled = NO; layer = <CALayer: 0x7ff3587432a0>>
   |    |    | <UIButton: 0x7ff358562e00; frame = (270.5 4.5;  ); opaque = NO; layer = <CALayer: 0x7ff358562d00>>
   |    |    |    | <UIImageView: 0x7ff358493320; frame = (2.5 2.5;  ); clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x7ff3584934d0>>
   |    |    | <UIImageView: 0x7ff358784340; frame = ( 7.5;  ); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x7ff35877b4d0>>
   |    |    | <UITextFieldLabel: 0x7ff3585524b0; frame = (- -;  ); text = 'p'; opaque = NO; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7ff3585526c0>>
   |    | <UINavigationButton: 0x7ff358470020; frame = ( ;  ); opaque = NO; layer = <CALayer: 0x7ff35840ad70>>
   |    |    | <UIButtonLabel: 0x7ff35a82e430; frame = ( ;  20.5); text = 'Cancel'; opaque = NO; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7ff35a82e6e0>>

//UINavigationButton是私有类，可以使用NSClassFromString转换过来
for (UIView *view in [[[self.searchBar subviews] objectAtIndex:] subviews]) {

        if ([view isKindOfClass:[NSClassFromString(@"UINavigationButton") class]]) {
            UIButton *btn = (UIButton *)view;
            btn.enabled = YES;
        }

}