CODEWITHSUNDEEP
iphoneobjective-ccocoacocoa-touchmacos
Johan Kool
Johan Kool

Reputation: 15927

Check if constant is defined at runtime in Obj-C

To, for example, access variables in a NSDictionary Cocoa frameworks often define keys, such as UIKeyboardBoundsUserInfoKey. How can I check if a key is defined at runtime? I found examples on how to check for classes and functions, but not for constants.

Upvotes: 20

Views: 4516

Answers (2)

Nathan de Vries
Nathan de Vries

Reputation: 15511

Jasarien's answer is roughly correct, but is prone to issues under LLVM 1.5 where the compiler will optimise the if-statement away.

You should also be comparing the address of the constant to NULL, rather than nil (nil has different semantics).

A more accurate solution is this:

BOOL isKeyboardBoundsKeyAvailable = (&UIKeyboardBoundsUserInfoKey != NULL);
if (isKeyboardBoundsKeyAvailable) {
  // UIKeyboardBoundsUserInfoKey defined
}

Upvotes: 46

Jasarien
Jasarien

Reputation: 58448

Check it's pointer against nil, like this

if (&UIKeyboardBoundsUserInfoKey != nil)
{
    //Key exists
}

Upvotes: 30

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