在 iOS 上使用機器學習套件翻譯文字

您可以使用 ML Kit 在語言之間翻譯文本。 ML Kit 目前支持59 種語言之間的翻譯。

在你開始之前

如果您尚未將 Firebase 添加到您的應用，請按照入門指南中的步驟進行操作。
在您的 Podfile 中包含 ML Kit 庫：
```
pod 'Firebase/MLNLTranslate', '6.25.0'
```
安裝或更新項目的 Pod 後，請務必使用其.xcworkspace打開您的 Xcode 項目。
在您的應用中，導入 Firebase：
迅速
```
import Firebase
```
Objective-C
```
@import Firebase;
```

翻譯一串文本

要在兩種語言之間翻譯字符串：

創建一個Translator對象，使用源語言和目標語言對其進行配置：

迅速

// Create an English-German translator:
let options = TranslatorOptions(sourceLanguage: .en, targetLanguage: .de)
let englishGermanTranslator = NaturalLanguage.naturalLanguage().translator(options: options)

Objective-C

// Create an English-German translator:
FIRTranslatorOptions *options =
    [[FIRTranslatorOptions alloc] initWithSourceLanguage:FIRTranslateLanguageEN
                                          targetLanguage:FIRTranslateLanguageDE];
FIRTranslator *englishGermanTranslator =
    [[FIRNaturalLanguage naturalLanguage] translatorWithOptions:options];

如果不知道輸入文本的語言，可以先使用語言識別API 。（但請確保不要一次在設備上保留太多語言模型。）

確保所需的翻譯模型已下載到設備。在您知道模型可用之前，不要調用translate(_:completion:) 。

迅速

let conditions = ModelDownloadConditions(
    allowsCellularAccess: false,
    allowsBackgroundDownloading: true
)
englishGermanTranslator.downloadModelIfNeeded(with: conditions) { error in
    guard error == nil else { return }

    // Model downloaded successfully. Okay to start translating.
}

Objective-C

FIRModelDownloadConditions *conditions =
    [[FIRModelDownloadConditions alloc] initWithAllowsCellularAccess:NO
                                         allowsBackgroundDownloading:YES];
[englishGermanTranslator downloadModelIfNeededWithConditions:conditions
                                                  completion:^(NSError *_Nullable error) {
  if (error != nil) {
    return;
  }
  // Model downloaded successfully. Okay to start translating.
}];

語言模型大約 30MB，所以不要不必要地下載它們，只使用 WiFi 下載它們，除非用戶另有說明。您還應該刪除不需要的模型。請參閱顯式管理翻譯模型。

確認模型已下載後，將源語言中的文本字符串傳遞給translate(_:completion:) ：

迅速

englishGermanTranslator.translate(text) { translatedText, error in
    guard error == nil, let translatedText = translatedText else { return }

    // Translation succeeded.
}

Objective-C

[englishGermanTranslator translateText:text
                            completion:^(NSString *_Nullable translatedText,
                                         NSError *_Nullable error) {
  if (error != nil || translatedText == nil) {
    return;
  }

  // Translation succeeded.
}];

ML Kit 將文本翻譯成您配置的目標語言，並將翻譯後的文本傳遞給完成處理程序。

顯式管理翻譯模型

當您使用上述翻譯 API 時，ML Kit 會根據需要自動將特定語言的翻譯模型下載到設備。您還可以使用 ML Kit 的翻譯模型管理 API 明確管理您希望在設備上可用的翻譯模型。如果您想提前下載模型或從設備中刪除不需要的模型，這會很有用。

要獲取存儲在設備上的翻譯模型：

迅速

let localModels = ModelManager.modelManager().downloadedTranslateModels

Objective-C

NSSet<FIRTranslateRemoteModel *> *localModels =
    [FIRModelManager modelManager].downloadedTranslateModels;

要刪除模型：

迅速

// Delete the German model if it's on the device.
let deModel = TranslateRemoteModel.translateRemoteModel(language: .de)
ModelManager.modelManager().deleteDownloadedModel(deModel) { error in
    guard error == nil else { return }
    // Model deleted.
}

Objective-C

// Delete the German model if it's on the device.
FIRTranslateRemoteModel *deModel =
    [FIRTranslateRemoteModel translateRemoteModelWithLanguage:FIRTranslateLanguageDE];
[[FIRModelManager modelManager] deleteDownloadedModel:deModel
                                           completion:^(NSError * _Nullable error) {
                                               if (error != nil) {
                                                   return;
                                               }
                                               // Model deleted.
                                           }];

要下載模型：

迅速

// Download the French model.
let frModel = TranslateRemoteModel.translateRemoteModel(language: .fr)

// Keep a reference to the download progress so you can check that the model
// is available before you use it.
progress = ModelManager.modelManager().download(
    frModel,
    conditions: ModelDownloadConditions(
        allowsCellularAccess: false,
        allowsBackgroundDownloading: true
    )
)

如果您想通過NotificationCenter獲取下載狀態，請為firebaseMLModelDownloadDidSucceed和firebaseMLModelDownloadDidFail註冊觀察者。確保在觀察者塊中使用對self的弱引用，因為下載可能需要一些時間，並且在下載完成時可以釋放原始對象。例如：

NotificationCenter.default.addObserver(
    forName: .firebaseMLModelDownloadDidSucceed,
    object: nil,
    queue: nil
) { [weak self] notification in
    guard let strongSelf = self,
        let userInfo = notification.userInfo,
        let model = userInfo[ModelDownloadUserInfoKey.remoteModel.rawValue]
            as? TranslateRemoteModel,
        model == frModel
        else { return }
    // The model was downloaded and is available on the device
}

NotificationCenter.default.addObserver(
    forName: .firebaseMLModelDownloadDidFail,
    object: nil,
    queue: nil
) { [weak self] notification in
    guard let strongSelf = self,
        let userInfo = notification.userInfo,
        let model = userInfo[ModelDownloadUserInfoKey.remoteModel.rawValue]
            as? TranslateRemoteModel
        else { return }
    let error = userInfo[ModelDownloadUserInfoKey.error.rawValue]
    // ...
}

Objective-C

// Download the French model.
FIRModelDownloadConditions *conditions =
    [[FIRModelDownloadConditions alloc] initWithAllowsCellularAccess:NO
                                         allowsBackgroundDownloading:YES];
FIRTranslateRemoteModel *frModel =
    [FIRTranslateRemoteModel translateRemoteModelWithLanguage:FIRTranslateLanguageFR];

// Keep a reference to the download progress so you can check that the model
// is available before you use it.
self.downloadProgress = [[FIRModelManager modelManager] downloadModel:frModel
                                                           conditions:conditions];

如果您想通過NSNotificationCenter獲取下載狀態，請為FIRModelDownloadDidSucceedNotification和FIRModelDownloadDidFailNotification註冊觀察者。確保在觀察者塊中使用對self的弱引用，因為下載可能需要一些時間，並且在下載完成時可以釋放原始對象。

__block MyViewController *weakSelf = self;

[NSNotificationCenter.defaultCenter
 addObserverForName:FIRModelDownloadDidSucceedNotification
 object:nil
 queue:nil
 usingBlock:^(NSNotification * _Nonnull note) {
     if (weakSelf == nil | note.userInfo == nil) {
         return;
     }

     FIRTranslateRemoteModel *model = note.userInfo[FIRModelDownloadUserInfoKeyRemoteModel];
     if ([model isKindOfClass:[FIRTranslateRemoteModel class]]
         && model == frModel) {
         // The model was downloaded and is available on the device
     }
 }];

[NSNotificationCenter.defaultCenter
 addObserverForName:FIRModelDownloadDidFailNotification
 object:nil
 queue:nil
 usingBlock:^(NSNotification * _Nonnull note) {
     if (weakSelf == nil | note.userInfo == nil) {
         return;
     }

     NSError *error = note.userInfo[FIRModelDownloadUserInfoKeyError];
 }];