Objective-C 的隐藏功能 [关闭]

Objective-C 是一种面向对象的编程语言，最初由苹果公司开发并广泛用于 iOS 和 macOS 应用程序的开发。除了常见的语法和特性外，Objective-C 还具有一些隐藏功能，这些功能可以帮助开发者更高效地编写代码和实现一些有趣的功能。本文将介绍一些 Objective-C 的隐藏功能，并提供相应的案例代码。

objective-c
#import 
@interface MyClass : NSObject
- (void)originalMethod;
@end
@implementation MyClass
- (void)originalMethod {
    NSLog(@"This is the original method.");
}
@end
@implementation MyClass (Extension)
- (void)extendedMethod {
    NSLog(@"This is the extended method.");
}
+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        SEL originalSelector = @selector(originalMethod);
        SEL swizzledSelector = @selector(extendedMethod);
        
        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
        
        BOOL success = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        if (success) {
            class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MyClass *myObject = [[MyClass alloc] init];
        [myObject originalMethod];
    }
    return 0;
}

objective-c
#import 
@interface MyClass : NSObject
@end
@implementation MyClass
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MyClass *myObject = [[MyClass alloc] init];
        objc_setAssociatedObject(myObject, @"name", @"John", OBJC_ASSOCIATION_COPY);
        NSString *name = objc_getAssociatedObject(myObject, @"name");
        NSLog(@"Name: %@", name);
    }
    return 0;
}

objective-c
#import 
@interface MyClass : NSObject
@end
@implementation MyClass
- (void)forwardInvocation:(NSInvocation *)anInvocation {
    NSLog(@"Forwarding method: %@", NSStringFromSelector(anInvocation.selector));
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    if (aSelector == @selector(unknownMethod)) {
        return [NSMethodSignature signatureWithObjCTypes:"v@:"];
    }
    return [super methodSignatureForSelector:aSelector];
}
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MyClass *myObject = [[MyClass alloc] init];
        [myObject performSelector:@selector(unknownMethod)];
    }
    return 0;
}

objective-c
#import 
@interface MyClass : NSObject
@end
@implementation MyClass
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MyClass *myObject = [[MyClass alloc] init];
        NSString *name = @"John";
        
        objc_setAssociatedObject(myObject, @"name", name, OBJC_ASSOCIATION_ASSIGN);
        NSString *associatedName = objc_getAssociatedObject(myObject, @"name");
        NSLog(@"Associated name: %@", associatedName);
        
        name = nil;
        NSString *associatedNameAfterRelease = objc_getAssociatedObject(myObject, @"name");
        NSLog(@"Associated name after release: %@", associatedNameAfterRelease);
    }
    return 0;
}

objective-c
#import 
@interface MyClass : NSObject
@end
@implementation MyClass
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Class myClass = objc_getClass("MyClass");
        SEL newSelector = @selector(newMethod);
        
        // 创建一个新的方法实现
        IMP implementation = imp_implementationWithBlock(^(id self) {
            NSLog(@"This is a new method.");
        });
        
        // 动态地为类添加一个方法
        class_addMethod(myClass, newSelector, implementation, "v@:");
        
        // 调用新添加的方法
        [myClass performSelector:newSelector];
    }
    return 0;
}