Swizzling : Allows switching "existing selectors" implementation at runtime with "other selector"
Declaration:
void method_exchangeImplementations(Method m1, Method m2);
Swizzling allows you to write code that can be executed before or after
the original method is implemented.
Example: Creating Log method for tracking view controller appearing.
#import "UIViewController+Log.h"
@implementation UIViewController (Log)
+ (void)load {
static dispatch_once_t once_token;
dispatch_once(&once_token, ^{
SEL viewWillAppearSelector = @selector(viewDidAppear:);
SEL viewWillAppearLoggerSelector = @selector(log_viewDidAppear:);
Method originalMethod = class_getInstanceMethod(self, viewWillAppearSelector);
Method extendedMethod = class_getInstanceMethod(self, viewWillAppearLoggerSelector);
method_exchangeImplementations(originalMethod, extendedMethod);
});
}
- (void) log_viewDidAppear:(BOOL)animated {
[self log_viewDidAppear:animated];
NSLog(@"viewDidAppear executed for %@", [self class]);
}
@end
