How to re-initialize a lazy property from another view?

Question

I have data that I want to read from disk into memory that takes a nontrivial amount of time. I want to be able to do two things:

1. I don't the data to be read every time the view loads.
2. I want to be able to invoke it from another view.

lazy var data: [String: String] = {
    guard let data = readFromDisk() else { return [:] }
    return processData(data: data)
}()

Above code gets initialized only once when the view loads for the first time, which is perfect for eliminating unnecessary computation. The problem is I also want to be able to trigger it from another view when needed.

I tried to trigger re-initialization:

func getData() {
    guard let data = readFromDisk() else { return [:] }
    data = processData(data: data)
}

and invoke it from another view:

let vc = ViewController()
vc.getData()

but, doesn't work. I tried to see if I could use static since it's also lazy, but I get an error saying:

Instance member cannot be used on type 'ViewController'

Finally, I tried creating a separate class:

class DataImporter {
    var data: [String: String] {
        guard let data = readFromDisk() else { return [:] }
        return processData(data: data)
    }
    
    func readFromDisk() -> [String: String] {}
    func processData(data: [String: String]) -> [String: String] {}
}

and have the lazy property in ViewController:

lazy var importer = DataImporter()

thinking that instantiating a class achieves the dual effect of taking advantage of a lazy property and invoking it when needed:

let vc = ViewController()
vc.importer = DataImporter()

This instantiates the class about a hundred times for some reason which is not ideal.

Answer 1

I would suggest creating a function that loads the data into data and then whenever you need to reload data, simply reassign it.

class DataStore {
    lazy var data: [String: String] = loadData()

    func readFromDisk() -> Data? {...}

    func processData(data: Data) -> [String:String] { ... }

    func loadData() -> [String:String] {
        guard let data = readFromDisk() else { return [:] }
        return processData(data: data)
    }
}

let store = DataStore()
let data = store.data // only loaded here
store.data = store.loadData() // reloads the data

If you don't want the loadData function to be exposed, you can also create a separate reloadData function.

class DataStore {
    ...
    func reloadData() {
        data = loadData()
    }
}

and then instead of doing store.data = store.loadData(), simply call store.reloadData()