Question

I have a superclass called City and a bunch of subclasses that inherit from this class. For example London and NewYork. Each of these subclasses have their own unique methods and instance variables.

When my app launches I geocode the current location and instantiate the subclass depending on which city I’m currently in.

Right now I have multiple properties defined to access these classes, so

@property (nonatomic, strong) London *london;
@property (nonatomic, strong) NewYork *newYork;
...
...

I will only ever need one object of this type in existence at any one time so would only like one property defined to access this object. Something like

@property (nonatomic, strong) City *city;

Is there a way I can dynamically create the subclass I require without having to declare multiple properties?

Answer 1

You can definitely implement subclasses in Objective-C. You could do the following to instantiate a city:

self.city = [[NewYork alloc] init];

To call city-specific methods:

if ([self.city isKindOfClass:[NewYork class]])
{
      // call some NewYork methods e.g..
      [(NewYork *)self.city doNewYorkThing];
}
else if ([self.city isKindOfClass:[London class]])
{
      // call some London methods e.g.
      [(London *)self.city doLondonThing];
}

The methods “isKindOfClass:”, “isMemberOfClass:”, “conformsToProtocol:” and “respondsToSelector:” are useful class methods for you to get familiar with.