Objective C 中的“调用方法”或“发送消息”

Objective-C是一种面向对象的编程语言，最初由NeXT开发并用于NeXTSTEP操作系统。它后来被苹果公司采用，并成为iOS和macOS开发的主要编程语言。Objective-C中的一个重要概念是“调用方法”或“发送消息”。在本文中，我们将探讨这个概念，并提供一些案例代码来说明它的用法。

[对象 方法选择器];

objective-c
#import 
@interface Person : NSObject
- (void)sayHello;
@end
@implementation Person
- (void)sayHello {
    NSLog(@"Hello!");
}
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person *person = [[Person alloc] init];
        [person sayHello];
    }
    return 0;
}

objective-c
#import 
@interface Calculator : NSObject
- (int)add:(int)a to:(int)b;
@end
@implementation Calculator
- (int)add:(int)a to:(int)b {
    return a + b;
}
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Calculator *calculator = [[Calculator alloc] init];
        int result = [calculator add:5 to:10];
        NSLog(@"The result is %d", result);
    }
    return 0;
}

objective-c
#import 
@interface Printer : NSObject
- (void)printHello;
- (void)printGoodbye;
@end
@implementation Printer
- (void)printHello {
    NSLog(@"Hello!");
}
- (void)printGoodbye {
    NSLog(@"Goodbye!");
}
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Printer *printer = [[Printer alloc] init];
        SEL helloSelector = NSSelectorFromString(@"printHello");
        SEL goodbyeSelector = NSSelectorFromString(@"printGoodbye");
        
        [printer performSelector:helloSelector];
        [printer performSelector:goodbyeSelector];
    }
    return 0;
}