// As a local variable 
returnType (^blockName)(parameterTypes) = ^returnType(parameters) {  
    // Block code here 
}; 
    NSUInteger (^name)(NSUInteger) = ^NSUInteger(NSUInteger max){
        return 0;
    };
    name(2);

// As a property 
@property (nonatomic, copy) returnType (^blockName)(parameterTypes); 

@property(nonatomic,copy) void (^blockName)( NSInteger);

self.blockName = ....

// As a method parameter  函数声明
- (void)someMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName { 
   // Block code here 
}; 
-(void)someMethod:(NSUInteger (^)(NSString *)) blockName
{
    
}

// As an argument to a method call  函数调用
 
[someObject someMethodThatTakesABlock: ^returnType (parameters) { 
 
    // Block code here 
}];     
 [self someMethod:^NSUInteger(NSString *name) {
        return 0;
   }];

// As a typedef 
typedef returnType (^TypeName)(parameterTypes); 
typedef void (^blockName) (NSString*);

TypeName blockName = ^(parameters) { 
 
    // Block code here 
}; 
blockName bb = ^(NSString * parameterName)
    {
    };