Setup for Assets downloading(資源下載設(shè)置)

這里我們?nèi)稳幌蚰阏故救绾蝸韺?shí)現(xiàn)一個簡單的資源下載設(shè)置。首先，我們創(chuàng)建一個新的TargetType協(xié)議的實(shí)現(xiàn)

fileprivate static let assetDir: URL = {
  let directoryURLs = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
  return directoryURLs.first ?? NSTemporaryDirectory()
}()


enum Asset: TargetType {
  case star
  case checkmark

  var baseURL: URL { /* ... */ }

  var assetName: String {
    switch self {
    case .star: return "star.png"
    case .checkmark: return "checkmark.png"
    }
  }

  var path: String {
    return "/assets/" + assetName
  }

  var localLocation: URL {
    return assetDir.appendingPathComponent(assetName)
  }

  var downloadDestination: DownloadDestination {
    return { _, _ in return (self.localLocation, .removePreviousFile) }
  }

  var task: Task {
    return .download(downloadDestination)
  }

  /*
    Rest of TargetType
  */
}

然后使用AssetLoader來包裝MoyaProvider

final class AssetLoader {
  let provider = MoyaProvider<Assets>()

  init() { }

  func load(asset: Asset, completion: ((Result<URL, MoyaError>) -> Void)? = nil) {
    if FileManager.default.fileExists(atPath: asset.localLocation.path) {
      completion?(.success(asset.localLocation))
      return
    }

    provider.request(asset) { result in 
      switch result {
      case .success:
        completion?(.success(asset.localLocation))
      case let .failure(error):
        return completion?(.failure(error))
      }
    }
  }
}

這就完畢了.然后使用AssetLoader

final class TestViewModel {
    let loader: AssetLoader

    init(loader: AssetLoader = AssetLoader()) {
        self.loader = loader
    }

    func loadImage() {
        loader.load(asset: .star) { result in
            // handle the result
        }
    }
}

總結(jié) 這小節(jié)的核心:

1. 創(chuàng)建好一個資源下載器AssetLoader（它包裝了MoyaProvider對象）
2. 創(chuàng)建好一個資源下載的TargetType。
3. 如何使用AssetLoader