Storing data into class

I am currently working on my first bigger project and I was wondering whether there is some way of putting data into one class and then just rewriting them or making an instance for the class. I have got a data that are being downloaded in the first ViewController and if I want to use them on all of my 5 ViewControllers, I just pass them using delegates and make a lot of duplicates. As this way is very inefficient and also messy, I would like to have them stored in one class. When I made custom class for those data, when changing to another ViewController, the data get instantly deleted.

Solution

You have multiple options to access the same piece of data from multiple places. The way you use fully depends on your needs. Here are a few options:

Dependency injection: Here is a nice post about it. This is having some data in one VC and injecting it to the next one. It's a good approach if you don't need to persist that data and other objects depend on it.
Delegation: You can make a VC pass data to its delegate after something happens (like a user tap, you finished downloading some data, etc).
Notification Center: You can send notification within the app scope and make any object (like a ViewController) to observe for specific notifications. You can send data along with a notifications.
Singleton design pattern: You can use singletons in Swift like this:

class MySingleton {
  static let shared = MySingleton()

  var name = ""
}

// Assign name variable somewhere (i.e. in your first VC after downloading data)
MySingleton.shared.name = "Bob"

// In some other ViewController
myLabel.text = MySingleton.shared.name

UserDefaults: This is a storage you can use to store small pieces of data. Keep in mind that this is not a database, it will persist your data between app launches, but you should not use it to store large amounts of data.
CoreData: This is a a persistence framework for iOS to store data, like you would do in a server-side DB. It's not exactly a DB, because you don't access disk directly each time you read/write, CoreData loads all its content to memory to access it. You have other third party libraries to work with local persistency, like Realm.

Hope it helps!