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iOS

Posted by Kim Sorgalla
Kim Sorgalla
2,174 Points

How To Create Class Instances

As maybe most of us I am still on a beginner level, hence I need your help and would appreciate answers with a bit more details :)

1. Multiple method-calling

I am trying to create an iOS app to play sound with AVFoundation Framework. In a sample project I saw below code. I don't understand this. I looked into the NSBundle class reference and see that mainBundle and URLForResource are both methods of the same class. For me this means it has kind of the same hierarchy. But why can I call both methods at the same time as below?

let filePath = NSBundle.mainBundle().URLForResource(fileName, withExtension: fileExt)

2. Creating Class Instances

Is there 2 ways of creating instances of a class? Sometimes I see className() and sometimes className.xxx. So either it is created without calling any methods or it uses Dot-Notation to access methods. Is that also an instance then? I am confused :(

Thanks a lot for your help!

1 Answer

Jhoan Arango
Jhoan Arango
14,575 Points

Hello

This is not an easy answer.. lol

First question:

That's a chain of methods, basically what is happening is that NSBundle.mainBundle will return an instance of NSBundle, and then URLForResourse() will access that instance and returns a file name, if it exist. I made an example that does basically the same thing. You can put this in a playground in your Xcode and play with it so you can see the results.

Don't put too much attention to this example, it's just to show you the process of it. 

class Person {
    var name: String?
    var lastName: String?
    var secondName: String?
    var secondLastName: String?

    // Type method
    static func fullName() -> Person{
        // Here we are creating an instance of Person.
        let fullName = Person()
        fullName.name = "John"
        fullName.secondName = "Sebastian"
        fullName.lastName = "Arango"
        fullName.secondLastName = "Pacelli"
        return fullName
    }

    // Instance method
    func firstName(name: String?) -> String? {
        if name == self.name {
            return "There is a person with a name \(name!)"
        } else if name == self.secondName {
            return "There is a person with a second name \(name!)"
        } else {
            return nil
        }
    }

    // Instance method
    func lastName(lastName: String?) -> String? {
        if lastName == self.lastName {
            return "There is a person with a last name \(lastName!)"
        } else if lastName == self.secondLastName {
            return "There is a person with a second last name \(lastName!)"
        } else {
            return nil
        }
    }
}

var test = Person.fullName().firstName("Carlos")
var peter = Person.fullName().lastName("Pacelli")

Second question:

You create an instance of a class like this.

// Using the same class as the example above.

var person = Person()

// now you can access

person.name

Notice how I did Person(). There is nothing in the parenthesis since this class has no initializer.

If you have any more questions, please let me know. :)

Good luck

Kim Sorgalla
Kim Sorgalla
2,174 Points

WOW, thanks a lot man. A lot of my confusion is gone now :D Thanks for this very detailed answer + those lovely code snippets!