前言

本文参考了微信读书团队的文章，学习了runtime反射机制的强大。具体的demo工程

学习过程1

A和B想要通信（比如A想要B模块的某个能力），都是通过中间件进行调度，这里起名叫Mediator。Mediator并不会将A和B的.h文件import进来，怎么做到的呢？就是通过runtime的反射机制。如果B想要A模块的某个能力,A只需要在Mediator中开放这样一个能力接口，供B通过Mediator进行调用。
具体代码参考如下：

//  main.m
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/21.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "B.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        B *b = [[B alloc] init];
        [b print];
    }
    return 0;
}

//  Mediator.h
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/21.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface Mediator : NSObject

- (void)printInBFromA:(NSString *)str;

@end

NS_ASSUME_NONNULL_END

//  Mediator.m
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/21.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import "Mediator.h"

@implementation Mediator

- (void)printInBFromA:(NSString *)str {
    Class classA = NSClassFromString(@"A");
    id aInstance = [[classA alloc] init];
    [aInstance performSelector:NSSelectorFromString(@"print:") withObject:str];
}

@end

//  A.h
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/21.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface A : NSObject


@end

NS_ASSUME_NONNULL_END

//  A.m
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/21.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import "A.h"

@implementation A

- (void)print:(NSString *)str {
    NSLog(@"------> %@",str);
}

@end

//  B.h
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/21.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface B : NSObject

- (void)print;

@end

NS_ASSUME_NONNULL_END

//  B.m
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/21.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import "B.h"
#import "Mediator.h"

@implementation B

- (void)print {
    Mediator *mediator = [[Mediator alloc] init];
    [mediator printInBFromA:@"hello"];
}

@end

学习过程2

如果说需要传入的参数不止2个（performSelector最多只支持两个），我们可以通过dict的形式进行传参数。

学习过程3

如果说Mediator需要提供的接口实在太多，我们可以通过Category，让各自提供方的模块制作Mediator的Category。Category文件依旧放在Mediator所在的模块中。

//  Mediator+A.h
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/22.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import "Mediator.h"

NS_ASSUME_NONNULL_BEGIN

@interface Mediator (A)

- (void)printInDFromA:(NSString *)bookId count:(NSInteger)bookCount price:(CGFloat)bookPrice;

@end

NS_ASSUME_NONNULL_END

//  Mediator+A.m
//  MediatorProject
//
//  Created by hushunfeng on 2018/12/22.
//  Copyright © 2018 cmcc. All rights reserved.
//

#import "Mediator+A.h"

@implementation Mediator (A)

- (void)printInDFromA:(NSString *)bookId count:(NSInteger)bookCount price:(CGFloat)bookPrice {
    Class classA = NSClassFromString(@"A");
    id aInstance = [[classA alloc] init];
    NSDictionary *params = @{@"bookId":bookId,@"bookCount":@(bookCount),@"bookPrice":@(bookPrice)};
    [aInstance performSelector:NSSelectorFromString(@"printBook:") withObject:params];

}


@end

过程4

Mediator 每一个方法里都要写 runtime 方法，格式是确定的，这是可以抽取出来的。在Mediator中添加如下方法：

- (void)performTarget:(NSString *)targetName action:(NSString *)actionName params:(NSDictionary *)params {
    Class target = NSClassFromString(targetName);
    id targetInstance = [[target alloc] init];
    [targetInstance performSelector:NSSelectorFromString(actionName) withObject:params];
}