如何检测 Firebase 存储文件是否存在？

Question

我正在

FIRStorageReference

上编写一个 Swift 扩展来检测文件是否存在。我打电话给

metadataWithCompletion()

。如果未设置完成块的可选

NSError

，我认为可以安全地假设该文件存在。

如果设置了 NSError，则要么出现问题，要么文件不存在。关于处理 iOS 中的错误的 存储文档 指出

FIRStorageErrorCodeObjectNotFound

是我应该检查的错误类型，但它无法解决（可能 Swiftified 为更短的 .Name 样式常量？）并且我不是确定我应该检查什么。

如果在某处设置了

completion(nil, false)

，我想致电

FIRStorageErrorCodeObjectNotFound

。

这是到目前为止我的代码。

extension FIRStorageReference {
    func exists(completion: (NSError?, Bool?) -> ()) {
        metadataWithCompletion() { metadata, error in
            if let error = error {
                print("Error: \(error.localizedDescription)")
                print("Error.code: \(error.code)")

                // This is where I'd expect to be checking something.

                completion(error, nil)
                return
            } else {
                completion(nil, true)
            }
        }
    }
}

提前非常感谢。

Answer 1

您可以像这样检查错误代码：

// Check error code after completion
storageRef.metadataWithCompletion() { metadata, error in
  guard let storageError = error else { return }
  guard let errorCode = FIRStorageErrorCode(rawValue: storageError.code) else { return }
  switch errorCode {
    case .ObjectNotFound:
      // File doesn't exist

    case .Unauthorized:
      // User doesn't have permission to access file

    case .Cancelled:
      // User canceled the upload

    ...

    case .Unknown:
    // Unknown error occurred, inspect the server response
  }
}

Answer 2

这是一个简单的代码，我用它来检查用户是否已经通过 hasChild("") 方法获取了用户照片，参考在这里：
https://firebase.google.com/docs/reference/ios/firebasedatabase/interface_f_i_r_data_snapshot.html

希望这能有所帮助

let userID = FIRAuth.auth()?.currentUser?.uid

        self.databaseRef.child("users").child(userID!).observeEventType(.Value, withBlock: { (snapshot) in
            // Get user value
            dispatch_async(dispatch_get_main_queue()){
                let username = snapshot.value!["username"] as! String
                self.userNameLabel.text = username
                // check if user has photo
                if snapshot.hasChild("userPhoto"){
                    // set image locatin
                    let filePath = "\(userID!)/\("userPhoto")"
                    // Assuming a < 10MB file, though you can change that
                    self.storageRef.child(filePath).dataWithMaxSize(10*1024*1024, completion: { (data, error) in
                        let userPhoto = UIImage(data: data!)
                        self.userPhoto.image = userPhoto
                    })
                }

Answer 3

斯威夫特5

let storageRef = Storage.storage().reference().child("yourPath").child("\(someFile)") // eg. someVideoFile.mp4

print(storageRef.fullPath) // use this to print out the exact path that your checking to make sure there aren't any errors

storageRef.getMetadata() { (metadata: StorageMetadata?, error) in
        
    if let error = error {
        guard let errorCode = (error as NSError?)?.code else {
            print("problem with error")
            return
        }
        guard let err = StorageErrorCode(rawValue: errorCode) else {
            print("problem with error code")
            return
        }
        switch err {
           case .objectNotFound:
                print("File doesn't exist")
            case .unauthorized:
                print("User doesn't have permission to access file")
            case .cancelled:
                print("User cancelled the download")
            case .unknown:
                print("Unknown error occurred, inspect the server response")
            default:
                print("Another error occurred. This is a good place to retry the download")
        }
        return
    }
        
    // Metadata contains file metadata such as size, content-type.
    guard let metadata = metadata else {
        // an error occured while trying to retrieve metadata
        print("metadata error")
        return
    }
        
    if metadata.isFile {
        print("file must exist becaus metaData is a file")
    } else {
        print("file for metadata doesn't exist")
    }
        
    let size = metadata.size
    if size != 0 {
        print("file must exist because this data has a size of: ", size)
    } else {
        print("if file size is equal to zero there must be a problem"
    }
}

没有详细错误检查的较短版本：

let storageRef = Storage.storage().reference().child("yourPath").child("\(someFile)")
storageRef.getMetadata() { (metadata: StorageMetadata?, error) in
        
    if let error = error { return }
    
    guard let metadata = metadata else { return }
        
    if metadata.isFile {
        print("file must exist because metaData is a file")
    } else {
        print("file for metadata doesn't exist")
    }
        
    let size = metadata.size
    if size != 0 {
        print("file must exist because this data has a size of: ", size)
    } else {
        print("if file size is equal to zero there must be a problem"
    }
}

Answer 4

对于 FirebaseStorage (10.16.0)，请改用

StorageError

，因为在此版本中

objectNotFound

的错误代码变为

1

。

extension StorageReference {
    func fileExists() async throws -> Bool {
        do {
            let _ = try await self.getMetadata()
            return true
        } catch {
            if case StorageError.objectNotFound = error {
                return false
            } else {
                throw error
            }
        }
    }
}