互相耦合 delegate notification

eg：经理有一个任务要交给员工完成
需要Manager和Employee两个类，而且都是使用单例

1.互相耦合－－－最差的耦合方式

在这种情况下，经理和员工互相知道对方的存在
Manager.h

@interface Manager : NSObject
+ (instancetype)shareInstance;
- (void)beginPrintTask;//开始任务，
- (void)celebratePrintDone;//结束任务
@end

Manager.m

@implementation Manager
+ (instancetype)shareInstance
{
    static Manager * instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [Manager new];
    });
    return instance;
}
- (void)beginPrintTask{
    [[Employee shareInstance] doPrintJob];//告诉员工要去做任务
}

- (void)celebratePrintDone{
    NSLog(@"celebrate print done");
}
@end

Employee.h

@interface Employee : NSObject
+ (instancetype)shareInstance;
- (void)doPrintJob;
@end

Employee.m

@implementation Employee
+ (instancetype)shareInstance
{
    static Employee * instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [Employee new];
    });
    return instance;
}

- (void)doPrintJob{
    NSLog(@"doing printing job");
    [[Manager shareInstance] celebratePrintDone];//告诉经理任务完成
}
@end

在VIewController里面直接调用
[[Manager shareInstance] beginPrintTask];

delegate

使用delegate可以让员工不知道经理的存在，但经理知道员工的存在，员工需要一个协议
Manager.h

@interface Manager : NSObject
+ (instancetype)shareInstance;
- (void)beginPrintTask;//开始任务，
- (void)celebratePrintDone;//结束任务
@end

Manager.m

+ (instancetype)shareInstance
{
    static Manager * instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [Manager new];
    });
    return instance;
}
- (void)beginPrintTask{
    [Employee shareInstance].delegate = self;
    [[Employee shareInstance] doPrintJob];//告诉员工要去做任务
}

- (void)celebratePrintDone{
    NSLog(@"celebrate print done");
}

Employee.h

@protocol EmployeePrintDelegate <NSObject>

- (void)printJobDone;

@end

@interface Employee : NSObject
+ (instancetype)shareInstance;
- (void)doPrintJob;
@property (nonatomic, weak) id<EmployeePrintDelegate> delegate;
@end

Employee.m

@implementation Employee
+ (instancetype)shareInstance
{
    static Employee * instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [Employee new];
    });
    return instance;
}

- (void)doPrintJob{
    NSLog(@"doing printing job");
    if (_delegate) {
        [_delegate printJobDone];
    }
}
@end

notification

这种情况下，经理和员工互相不知道对方的存在
Manager.h

@interface Manager : NSObject
+ (instancetype)shareInstance;
- (void)beginPrintTask;//开始任务，
- (void)celebratePrintDone;//结束任务
@end

Manager.m

+ (instancetype)shareInstance
{
    static Manager * instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [Manager new];
    });
    return instance;
}
//监听通知
- (instancetype)init{
    self = [super init];
    if (self) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(celebratePrintDone) name:Notif_PrintTaskDone object:nil];
    }
    return self;
}

- (void)beginPrintTask{
    [[NSNotificationCenter defaultCenter] postNotificationName:Notif_beginPrintTask object:nil];
}

- (void)celebratePrintDone{
    NSLog(@"celebrate print done");
}

Employee.h

@interface Employee : NSObject
+ (instancetype)shareInstance;
- (void)doPrintJob;
@end

Employee.m

@implementation Employee
+ (instancetype)shareInstance
{
    static Employee * instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [Employee new];
    });
    return instance;
}
//监听通知
- (instancetype)init{
    self = [super init];
    if (self) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(doPrintJob) name:Notif_beginPrintTask object:nil];
    }
    return self;
}
- (void)doPrintJob{
    NSLog(@"doing printing job");
    [[NSNotificationCenter defaultCenter] postNotificationName:Notif_PrintTaskDone object:nil];
}
@end

再加上一个.h文件

#define Notif_beginPrintTask @"Notif_beginPrintTask"
#define Notif_PrintTaskDone @"Notif_PrintTaskDone"