pragma mark About Block

    //block的原型:  
    NSString *(^myBlock)(int);  
    //上面的代码声明了一个block(^)原型，名字叫做myBlock，包含一个int型的参数，返回值为NSString类型的指针。  
      
    //block的定义:  
    myBlock=^(int paramA){  
        return [NSString stringWithFormat:@"Passed number:%d",paramA];  
    };       
    myBlock(2);  

pragma mark e.g. Block Create And Usage

    //基本使用   返回值 UIImage object  
    UIImage *oldImage=[UIImage imageNamed:@"avatar"];  
    UIImage *(^myImageBlock)(UIImage*)=^(UIImage *image){  
        return image;  
    };  
    UIImage *newImage=myImageBlock(oldImage);  

//基本使用  无返回值  
NSString *string=@"";  
void (^logBlock)(NSString *)=^(NSString *paramStr){  
    NSLog(@"logBlock log:%@",paramStr);  
};  
logBlock(string);  

    //含有block参数的函数 比较常见的类型,如网络请求中的successfulBlock  
    //方法  
    - (void)turnNumberWithNumberA:(NSInteger)a NumberB:(NSInteger)b andMyBlock:(void(^)(int aa,int bb))myBlock{  
        int c=[[NSNumber numberWithInteger:a]intValue];  
        int d=[[NSNumber numberWithInteger:b]intValue];  
        myBlock(c,d);  
    }
    //调用  
    [self turnNumberWithNumberA:1 NumberB:2 andMyBlock:^(int aa, int bb) {  
        NSLog(@"aa is %d",aa);  
        NSLog(@"bb is %d",bb);  
    }];  

//block在两个视图的传值 Apush到B B消失时将textfield的值传回A  
//B.h  
typedef void (^ReturnTextBlock)(NSString *showText);//给block重命名,方便调用  
  
@interface B : UIViewController  
  
@property (nonatomic, copy) ReturnTextBlock returnTextBlock;//声明一个block属性  
  
- (void)returnText:(ReturnTextBlock)block;//加上后方便第A视图书写该block方法  
  
@end  

    //B.m  
    - (void)returnText:(ReturnTextBlock)block {//block的实现方法  
        self.returnTextBlock = block;  
    }  
    - (void)viewWillDisappear:(BOOL)animated {            
        if (self.returnTextBlock != nil) {  
            self.returnTextBlock(self.inputTF.text);//视图将要消失时候调用  
        }  
    }

//A.m需要push的时候调用  
B *bVC = [[B alloc]init];  
  
[bVC returnText:^(NSString *showText) {//定义B视图后调用block  
    self.showLabel.text = showText;  
}];

转载：http://blog.csdn.net/scott_cc/article/details/51152145
https://www.cnblogs.com/linzhengbo/p/5617602.html
http://blog.csdn.net/ysy441088327/article/details/7942928
http://www.jianshu.com/p/e03292674e60
http://www.jianshu.com/p/8696d78f88cf