Question

What kind of information is stored behind such an enum type thing? Example:

typedef enum {
    UIViewAnimationCurveEaseInOut,
    UIViewAnimationCurveEaseIn,
    UIViewAnimationCurveEaseOut,
    UIViewAnimationCurveLinear
} UIViewAnimationCurve;

I am not sure if I can safely add such an enum constant to an array. Any idea?

Answer 1

Enums in Objective-C are exactly the same as those in C. Each item in your enum is automatically given an integer value, by default starting with zero.

For the example you provided: UIViewAnimationCurveEaseInOut would be 0; UIViewAnimationCurveEaseIn would be 1, and so on.

You can specify the value for the enum if required:

typedef enum {
    UIViewAnimationCurveEaseInOut,
    UIViewAnimationCurveEaseIn = 0,
    UIViewAnimationCurveEaseOut,
    UIViewAnimationCurveLinear
} UIViewAnimationCurve;

This result of this would be: UIViewAnimationCurveEaseInOut is 0; UIViewAnimationCurveEaseIn is 0; UIViewAnimationCurveEaseOut is 1; and so on. However, for basic purposes you shouldn’t need to do anything like that; it just gives you some useful info to toy with.

It should be noted based on the above, that an enum can’t assume to be a unique value; different enum identifiers can be equal in value to each other.

Adding an enum item to a NSArray is as simple as adding an integer. The only difference would be that you use the enum identifer instead.

[myArray addObject:[NSNumber numberWithInt:UIViewAnimationCurveEaseInOut]];

You can check this out for yourself by simply outputting each enum to the console and checking the value it provides you with. This gives you the opportunity to investigate the details of how it operates. But for the most part you won’t really need to know on a day to day basis.