IOS: Enumeration Type Enum,ns_enum,ns_options

In general, we use the C-style enum keyword to define enumeration types.

[CPP]View Plaincopy

1. enum{
2. Uiviewanimationtransitionnone,
3. Uiviewanimationtransitionflipfromleft,
4. Uiviewanimationtransitionflipfromright,
5. Uiviewanimationtransitioncurlup,
6. Uiviewanimationtransitioncurldown,
7. } uiviewanimationtransition;

[CPP]View Plaincopy

2. Displacement Operation Enumeration Definition
4. enum {
6. Uiviewautoresizingnone = 0,
8. Uiviewautoresizingflexibleleftmargin = 1 << 0,
10. Uiviewautoresizingflexiblewidth = 1 << 1,
12. Uiviewautoresizingflexiblerightmargin = 1 << 2,
14. Uiviewautoresizingflexibletopmargin = 1 << 3,
16. Uiviewautoresizingflexibleheight = 1 << 4,
18. Uiviewautoresizingflexiblebottommargin = 1 << 5
20. };
22. typedef Nsuinteger Uiviewautoresizing;  //Use Nsuinteger where you can use uiviewautoresizing,//uiviewautoresizing equivalent to an alias of Nsuinteger.
24. So a uiviewautoresizing variable can be assigned directly to Nsuinteger.

An enumeration value is typically an int value of 4 bytes, which is 8 bytes on a 64-bit system.

After IOS6 and Mac OS 10.8, Apple introduced two macros to redefine the two enum types, essentially combining the enum definition with a typedef and using different macros to differentiate from the code perspective.

Ns_options is generally used to define the enumeration values of displacement-related operations, we can refer to the Uikit.framework header file, you can see a large number of enumeration definitions.

[CPP]View Plaincopy

2. typedef ns_enum (Nsinteger, uiviewanimationtransition) {
4. Uiviewanimationtransitionnone,//default starting from 0
6. Uiviewanimationtransitionflipfromleft,
8. Uiviewanimationtransitionflipfromright,
10. Uiviewanimationtransitioncurlup,
12. Uiviewanimationtransitioncurldown,
14. };
18. typedef ns_options (Nsuinteger, uiviewautoresizing) {
20. Uiviewautoresizingnone = 0,
22. Uiviewautoresizingflexibleleftmargin = 1 << 0,
24. Uiviewautoresizingflexiblewidth = 1 << 1,
26. Uiviewautoresizingflexiblerightmargin = 1 << 2,
28. Uiviewautoresizingflexibletopmargin = 1 << 3,
30. Uiviewautoresizingflexibleheight = 1 << 4,
32. Uiviewautoresizingflexiblebottommargin = 1 << 5
34. };

The two macros are defined in Foundation.framework's NSObjCRuntime.h:

[CPP]View Plaincopy < param name= "wmode" value= "Transparent" >

2. #if (__cplusplus && __cplusplus >= 201103L && (__has_extension (cxx_strong_enums) | | __has_feature ( objc_fixed_enum))) | | (!__cplusplus && __has_feature (objc_fixed_enum))
4. #define NS_ENUM (_type, _name) ENUM _name: _type _name; Enum _name: _type
6. #if (__cplusplus)
8. #define Ns_options (_type, _name) _type _name; Enum: _type
10. #else
12. #define Ns_options (_type, _name) enum _name: _type _name; Enum _name: _type
14. #endif
16. #else
18. #define NS_ENUM (_type, _name) _type _name; Enum
20. #define Ns_options (_type, _name) _type _name; Enum
22. #endif

Will

[CPP]View Plaincopy

1. typedef ns_enum (Nsinteger, uiviewanimationtransition) {

Expand to get: [CPP]View Plaincopy < param name= "wmode" value= "Transparent" >

1. typedef enum Uiviewanimationtransition:nsinteger uiviewanimationtransition;
2. Enum Uiviewanimationtransition:nsinteger {

From the enumeration definition, the essence of Ns_enum and Ns_options is the same, just literally distinguishing its use. Ns_enum is a general case, ns_options is generally used to define situations with displacement operations or characteristics (bitmask).

When actually used, you can define directly:

[CPP]View Plaincopy

1. typedef Enum:nsinteger {...}  Uiviewanimationtransition;

is equivalent to the definition above.

Reference Documentation:

1. http://nshipster.com/ns_enum-ns_options/

2.http://iamthewalr.us/blog/2012/11/ns_enum-and-ns_options/

IOS: Enumeration Type Enum,ns_enum,ns_options