Objective-C basic framework)

A framework is a software package that contains multiple classes.

Mac operations provide dozens of frameworks to help us quickly develop applications on MAC systems.Program.
In these frameworks, there are some basic frameworks, including: string (nsstring), number (nsnumber), array (nsarray), Dictionary (nsdictionary), set (nsset).
All the classes on the Basic Framework are irrelevant to the user interface.
To use these classes, you need to use the following statement in the program to import the header file of the basic framework:
# Import <Foundation/Foundation. h>
You can also import header files of the class to be used, such:
# Import <Foundation/nsstring. h>

These basic frameworks are the basis for Mac program development. The root class of the Basic Framework is the nsobject class.