Classification and extension of OC

1. classification

That is to say .h And then there is .m file

The role of classification ：

• Declare private methods （ Written in .m In file ）
• Decomposing huge class files
• hold frame The private method of

Characteristics of classification ：

• Runtime resolution
• You can add categories to system classes

What can be added to the classification ：

• Example method
• Class method
• agreement
• Instance attributes （ Compiler will not build set,get Methods and member properties . It can be used runtime To implement by yourself set,get Method ）

Source analysis shows that ：

• The method added by the classification can override the method of the original class
• It depends on the compilation order : Finally, the method in the compiled classification will take effect
• Classification with the same name will cause compilation error

2. Expand

Only .h file

The role of expansion ：

• Declare private properties
• Declare private methods
• Declare private member variables

The characteristics of expansion ：

• Compilation is a resolution
• Only the form of declaration exists , Most of the time, they are parasitic on the host class .m in
• Cannot add extension for system class

My related blog ：
iOS oc classification （Category）
ios oc Classify with related objects ( agreement ) Add attribute （ Associated references : Associative References）
iOS oc Expand （Extension）

Reference blog ：
OC Categories ( classification ) And expand
OC classification Category