Android ApiDemos樣本解析(45)：App->Text-To-Speech

從Android1.6(API Level 4)開始，Android平台開始支援文字到語音（TTS）功能，也就是“合成語音”，支援以聲音方式讀出文字。

目前Android TTS可以支援多種語言：English, French, German, Italian ,Spanish 等，也有公司提供了用於Android平台的中文TTS Engine。

TTS Engine 在讀出文字前，需要知道使用哪種語言，比如“Paris”的發音，英語和法語發音就不同。因此TTS使用的語音庫是跟語言相關的。在使用TTS之前需要調入相應的語音庫。

儘管Android平台支援TTS，但具體的裝置可能不內建某種語言的語音庫，Android TTS可以查詢需要的語音庫是否存在，不在的戶運行使用者選擇下載需要的語音庫：

[java] 
Intent checkIntent = new Intent(); 
checkIntent.setAction(TextToSpeech.Engine.ACTION_CHECK_TTS_DATA); 
startActivityForResult(checkIntent, MY_DATA_CHECK_CODE); 
Intent checkIntent = new Intent();
checkIntent.setAction(TextToSpeech.Engine.ACTION_CHECK_TTS_DATA);
startActivityForResult(checkIntent, MY_DATA_CHECK_CODE);

如果需要的語音庫存在，則result code為CHECK_VOICE_DATA_PASS，表示TTS可以開始工作，否則可以通知使用者下載指定的語音庫。如果需要的語音庫存在，則result code為CHECK_VOICE_DATA_PASS，表示TTS可以開始工作，否則可以通知使用者下載指定的語音庫。

[java]
private TextToSpeech mTts; 
protected void onActivityResult( 
 int requestCode, int resultCode, Intent data) { 
 if (requestCode == MY_DATA_CHECK_CODE) { 
 if (resultCode == TextToSpeech.Engine.CHECK_VOICE_DATA_PASS) { 
 // success, create the TTS instance  
 mTts = new TextToSpeech(this, this); 
 } else { 
 // missing data, install it  
 Intent installIntent = new Intent(); 
 installIntent.setAction( 
 TextToSpeech.Engine.ACTION_INSTALL_TTS_DATA); 
 startActivity(installIntent); 
 } 
 } 
} 
private TextToSpeech mTts;
protected void onActivityResult(
 int requestCode, int resultCode, Intent data) {
 if (requestCode == MY_DATA_CHECK_CODE) {
 if (resultCode == TextToSpeech.Engine.CHECK_VOICE_DATA_PASS) {
 // success, create the TTS instance
 mTts = new TextToSpeech(this, this);
 } else {
 // missing data, install it
 Intent installIntent = new Intent();
 installIntent.setAction(
 TextToSpeech.Engine.ACTION_INSTALL_TTS_DATA);
 startActivity(installIntent);
 }
 }
}
TextToSpeechActivity 介紹了TTS的一般用法，可以隨機讀出一個字串數組中的文字。

TextToSpeech的建構函式 ，第一個參數可以使用當前Activity，第二個參數為TTS 初始化後回呼函數onInit.

public TextToSpeech(Context context, TextToSpeech.OnInitListener listener)

例子中回呼函數定義如下：

[java] 
// Implements TextToSpeech.OnInitListener.  
public void onInit(int status) { 
 // status can be either TextToSpeech.SUCCESS or TextToSpeech.ERROR.  
 if (status == TextToSpeech.SUCCESS) { 
 // Set preferred language to US english.  
 // Note that a language may not be available, and the result will indicate this.  
 int result = mTts.setLanguage(Locale.US); 
 // Try this someday for some interesting results.  
 // int result mTts.setLanguage(Locale.FRANCE);  
 if (result == TextToSpeech.LANG_MISSING_DATA || 
 result == TextToSpeech.LANG_NOT_SUPPORTED) { 
 // Lanuage data is missing or the language is not supported.  
 Log.e(TAG, "Language is not available."); 
 } else { 
 // Check the documentation for other possible result codes.  
 // For example, the language may be available for the locale,  
 // but not for the specified country and variant.  
  
 // The TTS engine has been successfully initialized.  
 // Allow the user to press the button for the app to speak again.  
 mAgainButton.setEnabled(true); 
 // Greet the user.  
 sayHello(); 
 } 
 } else { 
 // Initialization failed.  
 Log.e(TAG, "Could not initialize TextToSpeech."); 
 } 
} 
// Implements TextToSpeech.OnInitListener.
public void onInit(int status) {
 // status can be either TextToSpeech.SUCCESS or TextToSpeech.ERROR.
 if (status == TextToSpeech.SUCCESS) {
 // Set preferred language to US english.
 // Note that a language may not be available, and the result will indicate this.
 int result = mTts.setLanguage(Locale.US);
 // Try this someday for some interesting results.
 // int result mTts.setLanguage(Locale.FRANCE);
 if (result == TextToSpeech.LANG_MISSING_DATA ||
 result == TextToSpeech.LANG_NOT_SUPPORTED) {
 // Lanuage data is missing or the language is not supported.
 Log.e(TAG, "Language is not available.");
 } else {
 // Check the documentation for other possible result codes.
 // For example, the language may be available for the locale,
 // but not for the specified country and variant.
 
 // The TTS engine has been successfully initialized.
 // Allow the user to press the button for the app to speak again.
 mAgainButton.setEnabled(true);
 // Greet the user.
 sayHello();
 }
 } else {
 // Initialization failed.
 Log.e(TAG, "Could not initialize TextToSpeech.");
 }
}
status為TextToSpeech.SUCCESS表示TextToSpeech Engine成功初始化，然後設定語言為英語，如果本機帶有英語的語音庫，就可以開使使用speak來讀出文本了。

下面代碼從數組HELLOS中隨機播放一句讀出：

[java] 
int helloLength = HELLOS.length; 
String hello = HELLOS[RANDOM.nextInt(helloLength)]; 
mTts.speak(hello, 
 TextToSpeech.QUEUE_FLUSH,  // Drop all pending entries in the playback queue.  
 null); 
int helloLength = HELLOS.length;
String hello = HELLOS[RANDOM.nextInt(helloLength)];
mTts.speak(hello,
 TextToSpeech.QUEUE_FLUSH,  // Drop all pending entries in the playback queue.
 null);
每個TTS Engine 使用一個隊列用於合成語音，TextToSpeech.QUEUE_FLUSH意味著清除隊列中內容，將本句放在隊列的首位， 而TextToSpeech.QUEUE_ADD表示添加到隊列的後面。

 

作者：mapdigit