How to access constant string in runtime using a string which holding its name?

Question

I have some constant strings defined in my @implementation file like:

static NSString * const contentDisplayDateKeyPath   = @"content.display_date";
static NSString * const contentIDKeyPath            = @"content.id";

Could I get the content of contentDisplayDateKeyPath use a string which holding the variable's name in runtime?

ex:

NSString *constantName = @"contentDisplayDateKeyPath"

[self valueForKey:constantName]

then I'll get content.display_date

Can this be achieved?

I am trying to achieve this by using CFBundleGetDataPointer

    CFBundleRef mainBundle = CFBundleGetBundleWithIdentifier(CFBridgingRetain([[NSBundle mainBundle] bundleIdentifier]));
    void *stringPointer = CFBundleGetDataPointerForName(mainBundle, CFBridgingRetain(obj));
    NSString *string = (__bridge NSString *)stringPointer;

But the stringPointer is always null.

Thanks for help

score 2 · Answer 1 · edited Nov 04 '19 at 14:51

2

This should do it for you.

NSString *__autoreleasing *string = (NSString*__autoreleasing*)dlsym(RTLD_DEFAULT, "<name of constant like PKPaymentNetworkVisa>");
NSLog(@"%@", *string);

edited Nov 04 '19 at 14:51

Ian Bytchek

8,804
6
46
72

answered Jun 26 '15 at 18:06

Matt Foley

921
1
8
24

score 0 · Accepted Answer · answered Nov 13 '13 at 09:43

0

Use a map with the key as the constant name and the value as the constant value:

static NSDictionary *_constants = @{

    @"contentDisplayDateKeyPath" : @"content.display_date",
    @"contentIDKeyPath"          : @"content.id",
    // etc.
};

...

NSString *constantName = @"contentDisplayDateKeyPath";
NSString *constantValue = _constants[constantName];

answered Nov 13 '13 at 09:43

trojanfoe

120,358
21
212
242

Thanks, I've already try your suggestion and this completely fulfills my needs. But I'm looking for another solution (like using CFBundleGetDataPointerForName) – YCK Nov 13 '13 at 10:10

score 0 · Answer 3 · edited May 23 '17 at 12:16

0

Another option is to encapsulate this into a singleton object and access your constants through read only properties. Check out What should my Objective-C singleton look like? to see the singleton design pattern.

edited May 23 '17 at 12:16

Community

1
1

answered Nov 13 '13 at 09:47

Magic Bullet Dave

9,006
10
51
81

score 0 · Answer 4 · edited May 23 '17 at 12:33

This question was answered here:

How do I lookup a string constant at runtime in Objective-C?

The solution worked perfectly for me.

You can use CFBundleGetDataPointerForName to lookup a constant's value at runtime

-(NSString *)lookupStringConstant:(NSString *)constantName 
{

    void ** dataPtr = CFBundleGetDataPointerForName(CFBundleGetMainBundle(), (__bridge CFStringRef)constantName);
    return (__bridge NSString *)(dataPtr ? *dataPtr : nil);
}

How to access constant string in runtime using a string which holding its name?

4 Answers4