iOS 的代理模式讨论

今天仔细研究了下代理模式，之前是只会用，不知道具体实现，更不会自己编写。

废话不多说，上代码！

1.拟定一份协议

//
//  AssistantDelegate.h
//  141018Test
//
//  Created by JieLee on 10/18/14.
//  Copyright (c) 2014 PUPBOSS. All rights reserved.
//

#import <Foundation/Foundation.h>

@protocol AssistantDelegate <NSObject>
- (void)heisthirsty;
- (void)heishungry;
@end

2.编写需要代理的类 (要有代理的成员变量)

.h文件

//
//  Professor.h
//  141018Test
//
//  Created by JieLee on 10/18/14.
//  Copyright (c) 2014 PUPBOSS. All rights reserved.
//

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

@interface Professor : NSObject
@property (nonatomic, weak) id<AssistantDelegate> assis;
- (void)thirsty;
- (void)hungry;
@end

.m文件

//
//  Professor.m
//  141018Test
//
//  Created by JieLee on 10/18/14.
//  Copyright (c) 2014 PUPBOSS. All rights reserved.
//

#import "Professor.h"

@implementation Professor
- (void)thirsty {

    NSLog(@"i am thirsty");
    [_assis heisthirsty];
}
- (void)hungry {

    NSLog(@"i am hungry");
    [_assis heishungry];
}
@end

3.编写实现代理的类 （要遵守代理协议）

.h文件

//
//  Assistant.h
//  141018Test
//
//  Created by JieLee on 10/18/14.
//  Copyright (c) 2014 PUPBOSS. All rights reserved.
//

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

@interface Assistant : NSObject <AssistantDelegate>
@end

.m文件

//
//  Assistant.m
//  141018Test
//
//  Created by JieLee on 10/18/14.
//  Copyright (c) 2014 PUPBOSS. All rights reserved.
//

#import "Assistant.h"

@implementation Assistant
- (void)heishungry {

    NSLog(@"give you food");
}
- (void)heisthirsty {

    NSLog(@"give you water");
}
@end

4.编写main函数

//
//  main.m
//  141018Test
//
//  Created by JieLee on 10/18/14.
//  Copyright (c) 2014 PUPBOSS. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Professor.h"
#import "Assistant.h"

int main(int argc, const char * argv[]) {

    Professor *p = [Professor new];
    p.assis = [Assistant new];
    [p hungry];
    [p thirsty];
    return 0;
}

5.运行结果

2014-10-19 00:07:33.328 141018Test[2527:90902] i am hungry
2014-10-19 00:07:33.330 141018Test[2527:90902] give you food
2014-10-19 00:07:33.330 141018Test[2527:90902] i am thirsty
2014-10-19 00:07:33.330 141018Test[2527:90902] give you water
Program ended with exit code: 0

即使删除了 Assistant 这个类，程序也不会报错。

方法名上面可以加 @required 和 @optional 来修饰。

举个栗子：

@protocol AssistantDelegate <NSObject>

@required //必须实现的方法
- (void)heisthirsty;

@optional //可选实现的方法
- (void)heishungry;
@end

请注意 不声明的话默认是 @required 但是 编译不会报错，因为 Obj-C 是弱语法

不过问题就来了，这样做岂不是特别耗性能？不管代理有没有实现方法，都会通知代理做这件事情。