Objective-c: NSString to enum

Question

So, I've got this definition:

typedef enum {
    red = 1,
    blue = 2,
    white = 3
} car_colors;

Then, I've got a variable of type car_colors: car_colors myCar;

The question is, I receive the color of the car in a NSString. It must be a NSString, I can't change that. How can I convert from NSString to car_colors type?

NSString *value = [[NSString alloc] initWithString:@"1"];
myCar = [value intValue]; // <-- doesn't work

any idea? thanks!

What exactly doesn't work? Put a breakpoint in the method where you're converting the string to an integer, you should be able to see exactly what part is going haywire. — Marc Charbonneau, May 29 '09 at 14:24

score 53 · Answer 1 · edited Dec 10 '15 at 01:43

53

here's an implementation using NSDictionary and the existing enum

in .h file:

typedef NS_ENUM(NSInteger, City) {
    Toronto         = 0,
    Vancouver       = 1
 };

@interface NSString (EnumParser)
- (City)cityEnumFromString;
@end

in .m file:

@implementation NSString (EnumParser)

- (City)cityEnumFromString{
    NSDictionary<NSString*,NSNumber*> *cities = @{
                            @"Toronto": @(Toronto),
                            @"Vancouver": @(Vancouver),
                            };
    return cities[self].integerValue;
}

@end

sample usage:

NSString *myCity = @"Vancouver";
City enumValue = [myCity cityEnumFromString];

NSLog(@"Expect 1, Actual %@", @(enumValue));

edited Dec 10 '15 at 01:43

ThomasW

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answered Jul 26 '09 at 19:48

This should be the accepted answer. Making your enums Arrays or Dictionaries is not a good way to approach this issue. – datWooWoo Oct 29 '15 at 21:18
Note that if it the precise values of the enum aren't important, then you don't need to specify the values. – ThomasW Dec 10 '15 at 01:51

Abizern · Accepted Answer · 2014-03-31T07:01:03.607

18

Rather than use an array, why not use a dictionary; You have the colour NSString as keys, and you return whatever NSNumber you want. Something like; (Long winded for clarity).

NSDictionary *carColourDictionary = @{@"Red": @1,
                                      @"Blue": @2,
                                      @"White": @3};

// Use the dictionary to get the number
// Assume you have a method that returns the car colour as a string:
// - (NSString *)colourAsString;
int carColour = carColourDictionary[object colourAsString];

edited Mar 31 '14 at 07:01

answered May 29 '09 at 14:27

Abizern

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Enum has a different meaning, we cant replace the enum with NSArray or NSDictionary. When you develop libraries you must use proper datatypes. This is not a optimal solution for it. – Anto Binish Kaspar Nov 02 '11 at 12:51
5

@AntoBinishKaspar The question wasn't about a library it was about working around a particular problem with a particular constraint. And who says you can't replace an enum with a dictionary? I'm not talking about a drop in replacement, I'm talking about a different way of approaching a solution. – Abizern Jan 05 '12 at 16:05

score 8 · Answer 3 · edited Dec 10 '15 at 01:53

8

You could also put the values in an array.

NSArray *carColorsArray = @[@"red", @"blue", @"white"];

You can then use indexOfObject to get the index of a particular string.

car_colors carColor = [carColorsArray indexOfObject:@"blue"] + 1;

edited Dec 10 '15 at 01:53

ThomasW

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answered May 29 '09 at 13:52

Tom Jefferys

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score 3 · Answer 4 · edited May 23 '17 at 12:10

3

There are a lot of great answers to this here: Converting between C enum and XML

They are basically the same as Abizern's, but are a little cleaner and easier to work with if your app does this string-to-enum conversion a lot. There are solutions which keep the string and enum definitions together, and ways to make the conversions each a single, easy-to-read line of code.

edited May 23 '17 at 12:10

Community

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1

answered Sep 05 '09 at 21:22

andyvn22

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score 1 · Answer 5 · answered Dec 08 '11 at 11:26

// ...
typedef enum {
    One = 0,
    Two,
    Three
} GFN;
// ...
#define kGFNPrefix @"GFNEnum_"
// ...
+ (NSString *)gfnToStr:(GFN)gfn {
    return [NSString stringWithFormat:@"%@%d", kGFNPrefix, gfn];
}

+ (GFN)gfnFromStr:(NSString *)str {
    NSString *gfnStr = [str stringByReplacingOccurrencesOfString:kGFNPrefix withString:@""];
    return [gfnStr intValue];
}
// ...

My choice =)

score -6 · Answer 6 · answered May 29 '09 at 15:09

-6

I found the solution:

if ([car_color isEqualToString:@"1"])
        return red;
if ([tipo_pdi isEqualToString:@"2"])
        return blue;
if ([tipo_pdi isEqualToString:@"3"])
        return white;

But I don't like this 'if' style, what if I had a thousand colors? Isn't there a more automatic solution?

answered May 29 '09 at 15:09

Hectoret

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4

A dictionary - As I said in my answer. – Abizern May 29 '09 at 15:12
I won't vote you down, but what you are doing is just wrong. The answer by @Tom is much better than doing this. – Brock Woolf Aug 24 '10 at 13:35

Objective-c: NSString to enum

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