What values should I use for iOS boolean states?该不该使用true和false作为bool值

Short answer: you should prefer YES and NO for setting foundation properties of type BOOL.

For the long answer, let's first see where are these constants defined:

• true and false are from stdbool.h; they are #define-d as 1 and 0
• TRUE and FALSE are from CFBase.h; they are #define-d as 1 and 0
• YES and NO are from NSObjCRuntime.h. This is where signed char is typedef-ed as BOOL, and its two values are #define-d as ((BOOL)1) and ((BOOL)0) or __objc_yes/__objc_no if objc_bool is supported.

The foundation classes consistently use BOOL, which is a typedef for signed char, to represent its boolean properties. Since the first two pairs get converted to int constants, using them may result in warnings, though it would probably work correctly anyway. The YES and NO constants, however, are defined in the most compatible way for your compiler, regardless of its version. Therefore, I would recommend using YES and NO consistently throughout your code.