Objective C消息调度机制[关闭]

Objective C是一种面向对象的编程语言，它在消息调度机制方面具有独特的特点。消息调度机制是Objective C的核心概念之一，它使得对象能够在运行时根据消息来调用相应的方法。在本文中，我们将探讨Objective C消息调度机制的原理，并通过案例代码来加深理解。

objective-c
Person *person = [[Person alloc] init];
[person sayHello];

objective-c
@interface Shape : NSObject
- (double)area;
@end
@implementation Shape
- (double)area {
    return 0.0;
}
@end
@interface Rectangle : Shape
@property(nonatomic, assign) double width;
@property(nonatomic, assign) double height;
@end
@implementation Rectangle
- (double)area {
    return self.width * self.height;
}
@end
@interface Circle : Shape
@property(nonatomic, assign) double radius;
@end
@implementation Circle
- (double)area {
    return M_PI * self.radius * self.radius;
}
@end

objective-c
Shape *shape1 = [[Rectangle alloc] init];
shape1.width = 5.0;
shape1.height = 10.0;
NSLog(@"Rectangle area: %f", [shape1 area]);
Shape *shape2 = [[Circle alloc] init];
shape2.radius = 5.0;
NSLog(@"Circle area: %f", [shape2 area]);

objective-c
@interface Person : NSObject
@end
@implementation Person
+ (BOOL)resolveInstanceMethod:(SEL)sel {
    if (sel == @selector(sayHello)) {
        class_addMethod([self class], sel, (IMP)sayHelloMethod, "v@:");
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}
void sayHelloMethod(id self, SEL _cmd) {
    NSLog(@"Hello!");
}
@end

objective-c
Person *person = [[Person alloc] init];
[person sayHello];