xamarin android 导出 tts 语音到文件

public void ExportToFile(BookPageModel bookPageModel, string filepath)
        {
            var path = System.IO.Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, LocalDataHelper.Context.PackageName, "audio.mp3");
            Java.IO.File f = new Java.IO.File(path);
            var result = tts.SynthesizeToFile("你好呀", null, f, "");
        }