Swift MessageKit - 无法转换“_?”类型的值到预期的参数类型 'URL?'

Question

我刚刚开始使用 MessageKit，并在 swift 中将我的代码更新到 4.2，并且一直在解决问题。然而，我正在使用 Firebase 聊天教程并在示例代码中遇到问题，这些问题引发了示例项目中不可见的错误。

无法转换“_?”类型的值到预期的参数类型 'URL?'

        completion(meta?.downloadURL())

Answer 1

假设你的问题大概是下面的

storage.child(channelID).child(imageName).putData(data, metadata: metadata) { meta, error in
  completion(meta?.downloadURL())
}

回答，swift4

storage.child(channelID).child(imageName).putData(data, metadata: metadata) { metaN, error in
    // then we check if the metadata and path exist
    // if the error was nil, we expect the metadata and path to exist
    // therefore if not, we return an error
    guard let metadata = metaN, let path = metadata.path else {
       completion(nil)
       return
    }
    // now we get the download url using the path
    // and the basic reference object (without child paths)
    self.getDownloadURL(from: path, completion: completion)
}

private func getDownloadURL(from path: String, completion:@escaping (URL?) -> Void) {
    let firebaseStorageUrl = "gs://yourApp-Firebase-Storage.appspot.com"
    let storageReference = Storage.storage().reference(forURL: firebaseStorageUrl)
    storageReference.child(path).downloadURL { (url, error) in
        completion(url)
    }
}

确保您已在 Firebase 中启用存储，如果失败则检查控制台错误

Swift MessageKit - 无法转换“_?”类型的值到预期的参数类型 'URL?'

Swift MessageKit - Cannot Convert value of type '_?' to expected argument type 'URL?'

swift

messagekit