ios block 实现函数回调

//A.h

#import <Foundation/Foundation.h>

@interface A : NSObject

- (void)delegate:(int (^)(int, int))block;

@end

//A.m

#import "A.h"

@implementation A

- (void)delegate:(int (^)(int, int))block{

    block(10,20);//自己的方法自己并没实际地执行，而是交由其它类来执行(譬如B类)

}

@end

//B.h

#import <Foundation/Foundation.h>

@interface B : NSObject

- (void)aMethod;

@end

//B.m

#import "B.h"

#import "A.h"

@implementation B

- (void)aMethod{

    A *a = [[[A alloc] init] autorelease];

    [a delegate:^int(int a, int b){return a + b;}];

    //delegate是A类的方法，但实际执行的时候还是在B类执行，这就是方法回调

    //通俗的理解就是B实现了A的方法，A自己并不实际执行自己的方法delegate

    //给B类来实现

}

@end

//AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    B *b = [[[B alloc] init] autorelease];

    [b aMethod];

    return YES;

}