Fetching the data

When using SWR, Gravity will cache your data and update your views, but you'll need to fetch & convert that Data into useful objects. Sometimes, Gravity can do that automatically for you if this Data can be represented as JSON. But otherwise, you'll be asked to provide a system to fetch and decode data.

Creating a fetcher#

The first thing you'll want is to subclass Fetcher, the class that defines the shared behavior that is common to all data fetchers. Make sure to define all the types of your object when subclassing Fetcher. In this example, we'll create a very basic data fetching that receives data from a URL and convert it as a plain String:

public class FetcherDecodeString: Fetcher<URL, String> {
    public override func encode(object: String) throws -> Data {
        return object.data(using: .utf8)!
    }
    public override func decode(data: Data) throws -> String {
        return String(data: data, encoding: .utf8) ?? "None"
    }
    
    public override func fetch(location url: URL, callback: @escaping (Data?, Error?) -> Void) throws {
        let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
            callback(data, error)
        }
        
        task.resume()
    }
}

Using the data processor#

Once we've defined our data processor, we can use it simply by passing an instance as an argument in the GravityStream property wrapper:

@SWR<URL, String>(key: URL(string: "https://example.org/api/endpoint")!, fetcher: FetcherDecodeString()) var api