SpeechSynthesiser - System.OperationCanceledException: '异步操作已取消。'

Question

我正在使用 VS2019 开发一个 winforms 应用程序。当表单关闭时，我试图停止讲话。我有一个由以下代码显示的类：

public static class Voice
{
    static SpeechSynthesizer speechSynthesizer = new SpeechSynthesizer();
    static Random rnd = new Random();

    public static void Speak1()
    {
        speechSynthesizer.SpeakAsyncCancelAll();
        speechSynthesizer.Volume = 100;
        speechSynthesizer.Rate = -1;

        speechSynthesizer.SelectVoiceByHints(VoiceGender.Female, VoiceAge.Child);

        int choice = rnd.Next(1, 7);


        switch (choice)
        {
            .....
        }
    }

    public static void Speak2(bool tryAgain)
    {
        speechSynthesizer.SpeakAsyncCancelAll();

        speechSynthesizer.Volume = 100;
        speechSynthesizer.Rate = -1;

        speechSynthesizer.SelectVoiceByHints(VoiceGender.Female, VoiceAge.Child);

        int choice = rnd.Next(1, 3);

        switch (choice)
        {
            //...
        }
        if (tryAgain)
        {
            speechSynthesizer.SpeakAsync("Try Again!");
        }
    }

    public static void ReadAloud(string message)
    {
        speechSynthesizer.SpeakAsyncCancelAll();
        speechSynthesizer.Volume = 100;
        speechSynthesizer.Rate = -1;

        speechSynthesizer.SelectVoiceByHints(VoiceGender.Female, VoiceAge.Child);

        speechSynthesizer.SpeakAsync(message);
    }

    public static void StopVoice()
    {
         speechSynthesizer.SpeakAsyncCancelAll();

    }
}

我从解决方案中的多个位置调用方法。我的问题是，当我想通过在表单关闭时调用 StopVoice 方法来停止语音合成器时，我收到错误消息：

System.OperationCanceledException: '异步操作已取消。'

我该如何解决这个错误？