Decode Data? from another publisher-CodePudding

I am trying to decode a Publisher in another file which is dataService.$data, it is:

@Published var data: Data? = nil

Before I was using a Networking manager and it returned AnyPublisher<Data, Error>

let dataDownload = NetworkingManager.download(url: url)

casaSubscription = dataService.$data
            .decode(type: [House].self, decoder: XMLDecoder())
            .sink(receiveCompletion: NetworkingManager.handleCompletion, receiveValue: { [weak self] (returnedCasas) in
                self?.house = returnedCasas
                self?.houseSubscription?.cancel()
            })

Instead of dataService.$data I had dataDownload and it all worked fine, but now, I try to use dataService.$data and it throws the error below

Instance method 'decode(type:decoder:)' requires the types 'Published<Data?>.Publisher.Output' (aka 'Optional<Data>') and 'Data' be equivalent

CodePudding user response：

Optional(Data) and Data are not the same type.

In Combine avoid optionals as much as possible.

A simple solution is to declare an empty Data instance

@Published var data = Data()

and filter it in the pipeline

casaSubscription = dataService.$data
    .filter{!$0.isEmpty}
    .decode(type: [House].self, decoder: XMLDecoder()) ...

Or – if you really want to keep the optional

casaSubscription = dataService.$data
    .compactMap{$0}
    .decode(type: [House].self, decoder: XMLDecoder()) ...