iOS中使用@方法快速创建对象

       

                在iOS中有大量的@打头的快捷写法，总结如下

NSString

@"My String"     //得到一个__NSCFConstantString类型的对象

NSNumber
@32     @3.22346432 
@YES 
@'V'  @3.2F  
//__NSCFNumber

NSArray

@[@"1",@"2",[NSNull
null]] 
//__NSArrayI最后的null也算一个元素

NSDictionary *dictionary=
@{                                                          
@"first":@[@"1",@"2",@"3",[NSNull
null]],                               

                           @"second":@3.14,

                           @"third":@"hello world"                                   
                                };

//__NSDictionaryI