当使用RecognizeAsync启动识别器时，出现NullReferenceException

Question

嗨，我目前正在开发一个程序，应该识别我的声音，然后写下它听到的，但是当我运行代码，我点击按钮启动recEngine，它说"类型'系统的未处理的异常。NullReferenceException'在System.Speech.dll中发生'，在提示中它说var之前可能是空的。但是我之前已经设置了变量，或者我做错了什么。

下面是代码

using System;
using System.Windows.Forms;
using System.Speech.Recognition;
namespace Voice_Recognition
{
    public partial class Form1 : Form
    {
        SpeechRecognitionEngine recEngine =  new SpeechRecognitionEngine();
        public Form1()
        {
            InitializeComponent();
        }
        private void BtnEnable_Click(object sender, EventArgs e)
        {

这是出现错误的行。

            recEngine.RecognizeAsync(RecognizeMode.Multiple);
            // BtnEnable.Enabled = false;
            BtnDisable.Enabled = true;
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            Choices commands = new Choices();
            commands.Add(new string[] { "say hello", "print my name" });
            GrammarBuilder Gbuilder = new GrammarBuilder();
            Gbuilder.Append(commands);
            Grammar grammar = new Grammar(Gbuilder);
            recEngine.LoadGrammarAsync(grammar);
            recEngine.SetInputToDefaultAudioDevice();
            recEngine.SpeechRecognized += recEngine_SpeechRecognized;
        }
        private void recEngine_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
        {
            switch (e.Result.Text)
            {
                case "say hello":
                    Log.Text += "nHello";
                    break;
                case "print my name":
                    Log.Text += "nMyname";
                    break;
            }
        }
        private void BtnDisable_Click(object sender, EventArgs e)
        {
            BtnEnable.Enabled = true;
            BtnDisable.Enabled = false;
            recEngine.RecognizeAsyncStop();
        }
    }
 }

提示菜单里写着:

-在调用

方法之前检查对象是否为空

-使用"new"关键字创建对象实例

Thanks in advance

Answer 1

一些看起来很奇怪的事情:

• 用recEngine.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(recEngine_SpeechRecognized);代替recEngine.SpeechRecognized += recEngine_SpeechRecognized;

• 当你开始识别时，语法可能还没有完成加载;

使用LoadGrammar代替LoadGrammarAsync(或为LoadGrammarCompleted添加处理程序)。

• 我总是发现为识别器显式指定文化信息(和语法)很方便，因为这可以防止对正在使用的语言产生误解。