Define member variables in objective-C

IOS:

If it is only for internal access, you can directly use _ XXX (underline), without your own definition, the compiler will automatically generate

If you need external access to this variable, you can use

@ Property xxx;

@ Synthesize xxx = _ XXX. In this way, the compiler will automatically generate the get and set functions. It can clearly indicate that this is an attribute that provides the set and get methods to external entities.

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