回调的代理（delegate）实现

#import <Foundation/Foundation.h>

@protocol SampleProtocol;

//声明核心类的属性和方法
@interface CoreManage : NSObject

@property(nonatomic,assign) id<SampleProtocol> delegate;

- (void)doMainWork;

@end


//声明协议中的接口函数
@protocol  SampleProtocol <NSObject>

@required
- (void)innerTaskCallBack:(int) innerTaskSerialNo;

@optional
- (void)resultDisplayCallBack:(NSString *)backInfo;

@end

#import "CoreManage.h"

@implementation CoreManage

@synthesize delegate=_delegate;

- (void)doMainWork
{
    NSLog(@"核心类完成工序0");
    NSLog(@"核心类完成工序1");
    [self.delegate innerTaskCallBack:2];//工序2通过外部类回调函数完成
    NSLog(@"核心类完成工序3");
    [self.delegate resultDisplayCallBack:@"成功"];//通过外部类回调函数显示任务完成结果
}

@end

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

@interface OuterClass : NSObject<SampleProtocol>

- (void)run;

@end

#import "OuterClass.h"


@implementation OuterClass

- (void)run
{
    CoreManage *coreManage=[[CoreManage alloc] init];
    coreManage.delegate=self;
    [coreManage doMainWork];
}

//回调函数1
- (void)innerTaskCallBack:(int) innerTaskSerialNo{
    NSLog(@"外部类的回调函数，完成工序%d",innerTaskSerialNo);
}

//回调函数2
- (void)resultDisplayCallBack:(NSString *)backInfo{
    NSLog(@"外部类的回调函数，输出完成结果：%@",backInfo);
}

@end