在Background Worker上检测到DisconectedContext

Question

所以我在C＃程序上遇到“检测到DisconectedContext”错误。这是我第一次与背景工作者合作，现在我对他们了解不多。所以这是与该问题相关的部分：

private void bt_crack_Click(object sender, EventArgs e)
    {
        if (isWorkbookProtected())
        {
            MessageBox.Show("Tem password");
            if (!worker.IsBusy)
            {
                worker.RunWorkerAsync();
            }
        }
        else
        {
            MessageBox.Show("Não tem password");
        }
    }


    private bool isWorkbookProtected()
    {
        try
        {
            workbook.Unprotect(string.Empty);
            return false;
        }
        catch (Exception e)
        {
            return true;
        }

    }



    private void worker_DoWork(object sender, DoWorkEventArgs e)
    {
        BackgroundWorker worker = sender as BackgroundWorker;
        Builder str = new StringBuilder();
        while (!worker.CancellationPending)
        {
            str.next();

            worker.ReportProgress(str.getCounter(), str.getCurrent());

        }
        e.Cancel = true;
    }



    private void bt_stop_Click(object sender, EventArgs e)
    {
        worker.CancelAsync();
    }

    private void worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {

        lb_string.Text = e.UserState as String;
        lb_attempts.Text = e.ProgressPercentage.ToString();
    }

    private void bt_exit_Click(object sender, EventArgs e)
    {
        System.Windows.Forms.Application.Exit();
    }

    private void Form1_Load(object sender, EventArgs e)
    {

    }

    private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        MessageBox.Show("Complete!");
    }

这是Builder界面：

    public interface Builder
        {
            string next();

            string getCurrent();

            int getCounter();
        }

StringBuilder继续无限地构建一个String。 那么，任何人都能解释一下这里发生了什么吗？

先谢谢。

编辑：这是我的StringBuilder类：

public class StringBuilder : Builder
{
    private Char[] current;
    private int counter;

    public const int MAX = 255;
    public const int MIN = 0;

    public StringBuilder()
    {
        counter = 0;
        char[] c = new char[1];
        c[0] = (char)MIN;

        current = c;
    }

    public string next()
    {
        current = buildNextString();
        counter++;
        return current.ToString();
    }

    public string getCurrent()
    {
        return current.ToString();
    }

    public int getCounter()
    {
        return counter;
    }

    private Char[] buildNextString()
    {
        Char[] c = current;
        c = checkChar(c, c.Length);
        return c;

    }

    private Char[] checkChar(Char[] c, int num)
    {
        if (num > 1)
        {
            if ((int)c[num - 1] == MAX)
            {
                c[num - 1] = (char)MIN;
                c[num - 2]++;
                c = checkChar(c, num - 1);
            }
            else
            {
                c[num - 1]++;
            }

        }
        else if (num == 1)
        {
            if ((int)c[num - 1] == MAX)
            {
                c[num - 1] = (char)MIN;
                c = addChar(c);
            }
            else
            {
                c[num - 1]++;
            }

        }

        return c;

    }

    private Char[] addChar(Char[] c)
    {
        Char[] n = new Char[c.Length + 1];
        n[0] = (char)Char.MinValue;

        for (int i = 0; i < c.Length; i++)
        {
            n[i + 1] = c[i];
        }

        return n;
    }

}