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

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:
I don't the data to be read every time the view loads.
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()