How do I use enumerated datatypes in Objective-C?

I'm working on several iOS projects where I think enumerated datatypes would be helpful to me. For example, I have a game where the player can walk in several directions. I could just define four constants with string values as kDirectionUp开发者_StackOverflow中文版, kDirectionDown, etc.

I think an enumerated type would be better here. Is that correct? If so, how do I define an enum here so that I can later compare values? (As in, if(someValue == kDirectionUp){})

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That sounds like the right thing to do.

It's really simple to create enums in Objective-C using C-style type definitions. For example, in one of my header files, I have the following type definition:

typedef enum {
  CFPosterViewTypePoster = 0,
  CFPosterViewTypeStart, // 1
  CFPosterViewTypeEnd,   // 2
  ....                   // 3
} CFPosterViewType;   

You define an object of CFPosterViewType and set it to one of the values:

CFPosterViewType posterType = CFPosterViewTypeStart;

When comparing CFPosterViewType values, it's as simple as doing the following:

if (posterType == CFPosterViewTypePoster) {
    // do something
}

Note that the commented out numbers in the enum above are implicit values. If you want to do something differently, say, define a bitmask, or anything else where you need the values to be different than the default, you'll need to explicitly define them.

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In a header file, define an enum type, e.g.:

// SomeHeaderFile.h
typedef enum {
    MOPlayerDirectionNone,
    MOPlayerDirectionUp,
    MOPlayerDirectionDown,
    …
} MOPlayerDirection;

Whenever you need to use MOPlayerDirection, #import that header file. You can then use it as a type as well as its possible values.

For instance:

#import "SomeHeaderFile.h"

@interface MOPlayer : NSObject {
    MOPlayerDirection currentDirection;
}

- (void)moveToDirection:(MOPlayerDirection)direction;
- (void)halt;
@end

and:

#import "SomeHeaderFile.h"
#import "MOPlayer.h"

@implementation MOPlayer

- (id)init {
    self = [super init];
    if (self) {
        currentDirection = MOPlayerDirectionNone;
    }
    return self;
}

- (void)moveToDirection:(MOPlayerDirection)direction {
    currentDirection = direction;

    switch (currentDirection) {
        case MOPlayerDirectionUp:
            // do something
            break;

        case MOPlayerDirectionDown:
            // do something
            break;
    }
}

- (void)halt {
    if (currentDirection != MOPlayerDirectionNone) {
        // do something
        currentDirection = MOPlayerDirectionNone;
    }
}

@end

If an enumeration is tightly related to a class, it’s common to define it in the same header file as the class declaration. In the example above, instead of defining MOPlayerDirection in SomeHeaderFile.h, you could define it in MOPlayer.h instead.

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Just define them at the top of your file:

enum    // direction types
{
    kDirectionUp = 0,
    kDirectionDown, // 1
    kDirectionLeft, // 2
    kDirectionRight // 3

};

then you can call as required:

if(someValue == kDirectionUp){ // do something }