Get a constant value using an NSString

[airslim]

Hello everyone,

Im wondering if there's a way to get a constant value using a string, for example I want to get a kABPersonFirstNameProperty @"kABPersonFirstNameProperty".

I tried something like:

SEL selector = NSSelectorFromString(@"kABPersonFirstNameProperty");
[self performSelector:selector];

but it didn't work, I know it's stupid because selectors are about calling functions not constants or variables.


Im struggling with the whole thing because I want to get a bunch of address book properties dynamically like:

NSArray *singlevalues = [NSArray arrayWithObjects: @"kABPersonFirstNameProperty", @"kABPersonLastNameProperty"];

So if there's an alternative, it will also help.

[smasher]

The KVC method valueForKey should do the trick -

NSString *value = [someObject valueForKey:kABPersonFirstNameProperty];

If kABPersonFirstNameProperty is a string already then you don't need the @"".

[airslim]

The problem is that kABPersonFirstNameProperty is not an NSString, it has a type of ABPropertyID. I found another way to get around that by converting it to an NSNumber like:

NSNumber *property = [[NSNumber alloc] initWithInt:kABPersonBirthdayProperty];

but when I do:

ABRecordCopyValue(person, (ABPropertyID)property);

my app crashes. Any idea ?

[smasher]

I see, you want to use a string to get the value of a const C variable; valueForKey only works on objects to get instance variables. C doesn't have that kind of reflection.

You'll need to make a C array of those property constants and an NSArray of the strings you want to use. Write a method that accepts a string, searches the NSArray for the index, and the returns the matching number (type ABPropertyID, not NSNumber) from the C array.

I can't imagine any other reliable way, because kABPersonBirthdayProperty might be "5" in one SDK/device and "7" in another. Anything else is making assumptions about the values of those variables.

[Duncan C]

Originally Posted by airslim

The problem is that kABPersonFirstNameProperty is not an NSString, it has a type of ABPropertyID. I found another way to get around that by converting it to an NSNumber like:

NSNumber *property = [[NSNumber alloc] initWithInt:kABPersonBirthdayProperty];

but when I do:

ABRecordCopyValue(person, (ABPropertyID)property);

my app crashes. Any idea ?

ABPropertyID is an integer constant.

There's no converting it to a name. It's a constant defined using a #define somewhere in the headers of Apple's frameworks.

To find out the value, you can use a log statement like this

NSLog(@"constant ABPropertyID = %d", ABPropertyID);

You can't convert it to an NSNumber and then cast that NSNumber back to an ABPropertyID type, because then you are passing an object as if it is a constant value. You are passing bad data to the ABRecordCopyValue, so of course it crashes.