CODEWITHSUNDEEP
swiftinitialization
Chris Morse
Chris Morse

Reputation: 334

How to call a class method in a convenience initializer in Swift

I am trying to consume an API where every object names its ID field differently. Example: Group.groupid, Team.teamid, etc.

I have a BaseAPIObject that has a required initializer that accepts a parsed JSON dictionary and a convenience initializer that takes just the ID field (the only required property of my class).

I've dealt with the changing id field names by adding a static aka "class" method that returns the ID field name and subclasses override that function to return their own field name.

The problem I have is that in my base class' convenience initializer I can't call self.dynamicType before I've called self.init() but I need the results of that static class function before I can properly construct my object.

public class BaseAPIObject {
    var apiID: String!
    var name: String?
    var createdBy: String?
    var updatedBy: String?

    //Construct from JSONSerialization Dictionary
    required public init(_ data: [String: AnyObject]) {
        name        = data["name"] as String?
        createdBy   = data["created_by"] as String?
        updatedBy   = data["updated_by"] as String?

        super.init()

        let idName = self.dynamicType.idFieldName()
        apiID = data[idName] as String?
    }

    /// Creates an empty shell object with only the apiID set. 
    /// Useful for when you have to chase down a nested object structure
    public convenience init(id: String) {
        // THIS is what breaks! I can't call self.dynamicType here
        // How else can I call the STATIC CLASS method?
        // in ObjC this would be as simple as self.class.getIdFieldName()
        let idFieldName = self.dynamicType.getIdFieldName()
        let data = [idFieldName: id]
        self.init(data)
    }

    //This gets overridden by subclasses to return "groupid" or whatever
    class func idFieldName() -> String {
        return "id"
    }
}

Question: How can I solve the problem of calling a subclass' class function before I run init on the instance itself?

Upvotes: 0

Views: 2231

Answers (1)

Bjorn
Bjorn

Reputation: 71950

Instead of creating a class function for figuring out the id, create init functions instead. Since you already have to create one of these functions per subclass, you're not really losing anything. The subclasses init function then calls the super's init with the id name.

Here's an example, I changed some of the properties of your group just for the sake of making the example simple to illustrate the concept.

public class BaseAPIObject {
    var objData: [String:String]

    required public init(_ data: [String: String]) {
        println("Data: \(data)")
        self.objData = data

    }

    public convenience init(id: String, idFieldName: String) {
        let data = [idFieldName: id]
        self.init(data)
    }
}

And then in your subclass, just conceptually something like this:

public class GroupObject: BaseAPIObject {
    public convenience init (id: String) {
        self.init(id: id, idFieldName: "group")
    }
}

let go = GroupObject(id: "foo")
println(go.objData["group"]!) //prints "foo"

Upvotes: 2

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