Foundation Framework

NSObject: 所有类的父类

      主要方法：

           1，-（NSString）description：Returns a string that describes the contents of the receiver. (required)；返回自我描述；

           2，-（id）copy     无实现  需自己去实现

           3，-（id）mutableCopy  无实现  需自己去实现

NSArray   不可变数组

         description:

                      1,once you create NSArray object, you cannot add or remove objects;

                      2,all the objects in NSArray are held onto  strongly;

                      3,usually create NSArray by @[];

        methods:

               -(NSInteger )count   retuen the length of array;

              -(id)objectAtIndex:(NSInteger)index    return the object of array  at index;

             -sortedArrayByUsingSelector:(SEL)  selector     sorted（排序）

NSmutableArray

      the subclass of NSArray

NSNumber

       decription:

            1,include int float double  bool enum

            2,usually creaye by @();

NSValue

NSData

NSDictionary

NSMutableDictionary

NSUserDefaults

            是一种共享字典，when even applaction  launching or exiting，it is still keep work;

            create by [NSUSerDefaults standardUserDefaults]；当我们需要存储我们的东西的时候需要同步一下调用[[NSUSerDefaults standardUserDefaults] synchronize]