Create Instance variables at runtime

Question

I want to create instance variables dynamically at runtime, and I want to add these variables to a category. The number of the instance variables may change based on the configuration/properties file which I am using for defining them.

Any ideas??

Answer 1

Use Associative References - this is tricky, but that is the mechanism invented specifically for your use case.

Here is an example from the link above: first, you define a reference and add it to your object using objc_setAssociatedObject; then you can retrieve the value back by calling objc_getAssociatedObject.

static char overviewKey;

NSArray *array = [[NSArray alloc] initWithObjects:@ "One", @"Two", @"Three", nil];
NSString *overview = [[NSString alloc] initWithFormat:@"%@", @"First three numbers"];

objc_setAssociatedObject (
    array,
    &overviewKey,
    overview,
    OBJC_ASSOCIATION_RETAIN
);
[overview release];

NSString *associatedObject = (NSString *) objc_getAssociatedObject (array, &overviewKey);
NSLog(@"associatedObject: %@", associatedObject);

objc_setAssociatedObject (
    array,
    &overviewKey,
    nil,
    OBJC_ASSOCIATION_ASSIGN
);
[array release];