iOS: create an object class with Swift

Question

I created this class for my object City

class City: NSObject {

    var _name:String = ""
    var name:String {
        get {
            return _name
        }
        set (newVal) {
            _name = newVal
        }
    }
}

then when I create my object I do:

var city:City!

city.name = "London" //crash here

println("name city is\(city.name)");

it crash when I set the name with message "fatal error: unexpectedly found nil while unwrapping an Optional value"

score 33 · Accepted Answer · answered Feb 09 '15 at 11:29

This is not actually an answer (see other answers for a solution, such as @Greg's and @zelib's), but an attempt to fix some mistakes I see in your code

No need to create computed + stored property (unless you have a reason for that):
```
class City: NSObject {
    var name: String = ""
}
```
If you inherit from NSObject, you automatically lose all swift features - avoid it (unless you have a reason for that)
```
class City {
    var name: String = ""
}
```
You are using an empty string as absence of value - swift provides optionals for that
```
class City {
    var name: String?
}
```
Alternative to 3., a city without a name wouldn't make much sense, so you probably want each instance to have a name. Use non optional property and an initializer:
```
class City {
    var name: String
    init(name: String) {
        self.name = name
    }
}
```
Avoid implicitly unwrapped optionals (unless you have a reason for that):
```
var city: City
```

@D4ttatraya: You're right, it's not an answer, it's like, five answers, #2 of which solved my particular problem. Good answers are rarely instantaneous. — HoldOffHunger, Jul 03 '18 at 23:08

Mithra Singam · Answer 2 · 2020-09-03T00:35:15.553

16

Just like any other object oriented programming language, and object should be initialized before accessing it.
Like:

var city:City

This is just reference of the object. So, actual memory is not created here. You need to create actual object for City Class.

Fix it by adding following statement:

city = City()

edited Sep 03 '20 at 00:35

answered Apr 05 '17 at 18:30

Mithra Singam

1,905
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score 6 · Answer 3 · answered Feb 09 '15 at 10:50

6

You haven't initialised the city variable and when you trying to use it it crash.

initialise it first before you use it:

city = City()
city.name = "London"

answered Feb 09 '15 at 10:50

Greg

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I have created a Mappable class so when I tried to initialise the class as you described then it shows suggestion ***Missing argument for parameter 'map' in call***. – Shiv Jaiswal Apr 26 '18 at 08:52
@ShivJ it sounds like your class needs a parameter for variable map. You should do something like that ClassName(map), this may also take a label (ClassName(map: map)). It's difficult to give you a definite answer without seeing the code. – Greg Apr 26 '18 at 09:09

score 4 · Answer 4 · answered Feb 09 '15 at 10:52

4

You are getting error because you are not initializing your city variable instead you just implicitly unwrap it without initializing at any stage. To initialize it you must use the following code

var city:City = City()

answered Feb 09 '15 at 10:52

Zell B.

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Best answer. Also, you can still initialize this way, too, ie.: var city:City = City(name: "someName") – HoldOffHunger Jul 03 '18 at 23:30

score 1 · Answer 5 · answered Feb 09 '15 at 11:14

1

You have to call the init method. So you would do it like this :

var city:City=City() //Calls init and creates an instance
city.name="foo"

If you don't define an init method(it's always a good practice that you do), the default init method is called.

answered Feb 09 '15 at 11:14

Dhruv Ramani

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iOS: create an object class with Swift

5 Answers5