Make all instances of UINavigationBar titles lowercase without subclassing?

问题

Some titles in this iOS app are defined in the storyboard. Some of the titles are being set programmatically. Is there a simple way (Obj-C categories maybe?) to make all the titles lowercase without subclassing?

回答1:

It is possible with a bit of objective-c magic, using method_exchangeImplementations (AKA "Method Swizzling")

#import <objc/runtime.h>

@interface UINavigationItem (New)
@end

@implementation UINavigationItem (New)

- (void)setTitleLower:(NSString *)title {
    [self setTitleLower:[title lowercaseString]];
}

+ (void)load {
    method_exchangeImplementations(class_getInstanceMethod(self, @selector(setTitle:)), class_getInstanceMethod(self, @selector(setTitleLower:)));
}

@end

Now each call to someNavItem.title = @"Whatever" ([UINavigationItem setTitle:(NSString*)title]) should go through setTitleLower, which in turn also calls the original setTitle with a minor modification, lowercasing the title.

I would avoid having to implement such a category just for the sake of lower-casing all titles for each UINavigationItem. I guess you're experimenting categories.

来源：https://stackoverflow.com/questions/17625221/make-all-instances-of-uinavigationbar-titles-lowercase-without-subclassing