C enum definition in iOS framework class

Question

I am browsing the UIKit framework header files and I see a lot of instances where an anonymous enum is defined followed by a seemingly related typedef. Can someone explain what is going on here?

Does the UIViewAutoresizing type somehow (implicitly) refer to the enum declared in the previous statement? How would you refer to that enum type?

enum {
    UIViewAutoresizingNone                 = 0,
    UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
    UIViewAutoresizingFlexibleWidth        = 1 << 1,
    UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
    UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
    UIViewAutoresizingFlexibleHeight       = 1 << 4,
    UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};
typedef NSUInteger UIViewAutoresizing;

JustSid · Accepted Answer · 2012-02-13 17:32:50Z

3

The thing is that those are flags intended to use as bit mask, which leads to problems with enums. For example, if it would look like this:

typedef enum {
    UIViewAutoresizingNone                 = 0,
    UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
    UIViewAutoresizingFlexibleWidth        = 1 << 1,
    UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
    UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
    UIViewAutoresizingFlexibleHeight       = 1 << 4,
    UIViewAutoresizingFlexibleBottomMargin = 1 << 5
} UIViewAutoresizing;

And you would call setAutoresizingMask: on a view with UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight, the compiler will complain and you must explicitly typecast it back to the UIViewAutoresizing type. The NSUInteger however can take the bit mask.

Beside that, everything that lef2 said about NSUInteger not being an ObjC object.

answered Feb 13, 2012 at 17:32

JustSid

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2 Comments

Keith Over a year ago

So the anonymous enum is only declaring symbolic names for constant vales (similar to #define) and the typedef is related to the enum by the naming convention only (UIViewAutoresizing___)? I think that makes sense

JustSid Over a year ago

@Keith: Yes, thats correct. The compiler enforcement of passing the right types to the enum isn't desired in these cases, it even is counter intuitive. In cases were it is desired, Apple uses a typedefed enum.

v1Axvw · Accepted Answer · 2012-02-13 17:56:32Z

3

I think you've only got one thing wrong here: NSUInteger is not an objective-c object it is an unsigned int on 32-bit systems and an unsigned long on 64-bit systems. So actually this is what's going on:

typedef unsigned int UIViewAutoresizing;

or

typedef unsigned long UIViewAutoresizing;

For more reference I add this:

#if __LP64__ || NS_BUILD_32_LIKE_64
typedef long NSInteger;
typedef unsigned long NSUInteger;
#else
typedef int NSInteger;
typedef unsigned int NSUInteger;
#endif

Source: CocoaDev

edited Feb 13, 2012 at 17:56

answered Feb 13, 2012 at 17:28

v1Axvw

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1 Comment

JustSid Over a year ago

Err, its vice versa. An int on 32 bit system, a long on 64 bit systems.

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