UtteranceProgressListener回调未触发

前言

日前在书写一个voice lib时使用到了TextToSpeech，设置了UtteranceProgressListener但是回调却没有被触发，对此问题进行了查询和解决。

问题分析

在TextToSpeech调用speak方法时我采用了如下代码：

textToSpeech.speak(playText, TextToSpeech.QUEUE_ADD, null,null)

查看文档上对于UtteranceProgressListener的说明，有如下一段描述：

Listener for events relating to the progress of an utterance through the synthesis queue. Each utterance is associated with a call to TextToSpeech#speak or TextToSpeech#synthesizeToFile with an associated utterance identifier, as per TextToSpeech.Engine#KEY_PARAM_UTTERANCE_ID. The callbacks specified in this method can be called from multiple threads.

这提示了UtteranceProgressListener需要设置utteranceId，而我上述代码设置了null，在修改之后发现回调已经可以被正常触发了。