IOS开发Objective-C Runtime使用示例详解

[array insertObject:obj atIndex:5];

objc_msgSend(array, @selector(insertObject:atIndex:), obj, 5);

void dynamicXXXMethod(id obj, SEL _cmd) {
    NSLog(@"ok...");
}
+ (BOOL)resolveInstanceMethod:(SEL)aSEL {
    if(aSEL == @selector(xxx:)) {
        class_addMethod([self class], aSEL, (IMP)dynamicXXXMethod, "v@:");
        return YES;
    }
    return [super resolveInstanceMethod];
}

- (id)forwardingTargetForSelector:(SEL)aSelector {
    if(aSelector == @selector(xxx:)){
        return otherObject;
    }
    return [super forwardingTargetForSelector:aSelector];
}

//根据 SEL 生成 NSInvocation 对象，然后再由 -forwardInvocation: 方法进行转发。
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    NSMethodSignature *signature = [super methodSignatureForSelector:aSelector];
    if (!signature) {
        signature = [otherObject instanceMethodSignatureForSelector:aSelector];
    }
    return signature;
}
- (void)forwardInvocation:(NSInvocation *)invocation {
    SEL sel = invocation.selector;
    if([otherObject respondsToSelector:sel]) {
        [invocation invokeWithTarget:otherObject]; // 转发消息
    } 
    else {
        [self doesNotRecognizeSelector:sel]; // 抛出异常
    }
}

@interface NSObject (JC)
@property (nonatomic, copy) NSString *ID;
@end
@implementation NSObject (JC)
static const void *IDKey;
- (NSString *)ID {
    return objc_getAssociatedObject(self, &IDKey);
}
- (void)setID:(NSString *)ID {
    objc_setAssociatedObject(self, &IDKey, ID, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
@end  

#import <objc/runtime.h> 
@implementation UIViewController (Tracking) 
+ (void)load { 
    static dispatch_once_t onceToken; 
    dispatch_once(&onceToken, ^{ 
        Class aClass = [self class]; 
        SEL originalSelector = @selector(viewWillAppear:); 
        SEL swizzledSelector = @selector(swizzled_viewWillAppear:); 
        Method originalMethod = class_getInstanceMethod(aClass, originalSelector); 
        Method swizzledMethod = class_getInstanceMethod(aClass, swizzledSelector); 
        // 如果要对类方法进行交换，使用下面注释的代码
        // Class aClass = object_getClass((id)self);
        // 
        // Method originalMethod = class_getClassMethod(aClass, originalSelector);
        // Method swizzledMethod = class_getClassMethod(aClass, swizzledSelector);
 		// 交换两个方法的实现
 		// 防止 aClass 不存在 originalSelector，所以添加一下试试，但指向地址为新方法地址
        BOOL didAddMethod = class_addMethod(aClass, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod)); 
        if (didAddMethod) { 
        	// 添加成功，说明 aClass 不存在 originalSelector，所以替换 swizzledSelector 的 IMP 为 originalMethod，实质上它们都指向 swizzledMethod
            class_replaceMethod(aClass, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod)); 
        } 
        else { 
         	// 添加失败，说明 aClass 存在 originalSelector，直接交换
            method_exchangeImplementations(originalMethod, swizzledMethod); 
        } 
    }); 
} 
#pragma mark - Method Swizzling 
// 由于方法实现已经被交换，所以系统在调用 viewWillAppear: 时，实际上会调用 swizzled_viewWillAppear:
- (void)swizzled_viewWillAppear:(BOOL)animated { 
	// 下面代码表面上看起来会引起递归调用，由于函数实现已经被交换，实际上会调用 viewWillAppear:
   [self swizzled_viewWillAppear:animated]; 
	// 在原有基础上添加其它功能(写日志等)
} 
@end