如何阻止MainForm处理时关闭？e.Cancel不生效问题排查

核心问题 #

1. 错误的主窗口实例：在Books.cs的btnClick方法中，你新建了一个MainForm实例MainForm mainform = new MainForm();，但这个实例并非当前正在显示的主窗口。调用SetProcessingState修改的是这个新实例的isProcessing字段，而非实际运行的主窗口状态，导致主窗口FormClosing事件中isProcessing始终为false，无法触发关闭阻止逻辑。同时这个新实例从未显示，它的FormClosing事件自然不会触发。
2. 事件绑定可能缺失：如果主窗口的FormClosing事件未在设计器或代码中正确绑定到MainForm_FormClosing方法，断点也不会触发。

修复步骤 #

1. 传递当前主窗口实例给Books.cs #

修改Books.cs的btnClick方法，接收当前运行的MainForm实例，而非新建：

// Books.cs
private async Task btnClick(MainForm mainForm) // 接收外部传入的主窗口实例
{
    // 移除新建MainForm的代码：MainForm mainform = new MainForm();
    try
    {
        mainForm.SetProcessingState(true);

        cts = new CancellationTokenSource();

        PleaseWait pleasewait = new PleaseWait();
        pleasewait.Closed += PleaseWait_Closed;
 
        pleasewait.Show();

        try
        {
            // 通过主窗口实例获取Excel路径
            string path = mainForm.TxtBox.Text;
            await Task.Run(() => ProcessBookstoreExcel(cts.Token, path));
        }
        catch(OperationCanceledException)
        {
            cancel = true;
            pleasewait.Close();
            // MessageBox.Show("操作已取消");
        }
        catch(Exception ex)
        {
            pleasewait.Close();
            MessageBox.Show(ex.Message);
        }
        pleasewait.Closed -= PleaseWait_Closed;
        pleasewait.Close();

        if(!cancel)
            MessageBox.Show("处理完成！");
    }
    catch(Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
    finally
    {
        cts?.Dispose();
        cts = null;
        mainForm.SetProcessingState(false);
    }
}

// 修改ProcessBookstoreExcel方法，接收路径参数
private void ProcessBookstoreExcel(CancellationToken cancellationToken, string path)
{
    try
    {
        ExcelPackage.LicenseContext = LicenseContext.NonCommercial;
        var records = new List<BookRecord>();

        using (var package = new ExcelPackage(new FileInfo(path)))
        {
            ExcelWorksheet worksheet = package.Workbook.Worksheets[0];
            int rowCount = worksheet.Dimension.Rows;

            for (int row = 2; row <= rowCount; row++)
            {
                cancellationToken.ThrowIfCancellationRequested();

                records.Add(new BookRecord
                {
                    LineNumber = row,
                    ISBN = worksheet.Cells[row, 1].Text,
                    Title = worksheet.Cells[row, 2].Text,
                    Stock = int.Parse(worksheet.Cells[row, 3].Text),
                    Price = decimal.Parse(worksheet.Cells[row, 4].Text),
                    PublisherID = int.Parse(worksheet.Cells[row, 5].Text),
                    PublisherName = worksheet.Cells[row, 6].Text
                });
            }
        }

        var discrepancies = new List<Discrepancy>();
        var groupedRecords = new Dictionary<string, Dictionary<string, (decimal Price, int Stock)>>();

        foreach (var record in records)
        {
            cancellationToken.ThrowIfCancellationRequested();
 
            var publisherKey = record.PublisherID.ToString();
            var isbnKey = record.ISBN;

            if (!groupedRecords.ContainsKey(publisherKey))
            {
                groupedRecords[publisherKey] = new Dictionary<string, (decimal Price, int Stock)>();
            }

            if (!groupedRecords[publisherKey].ContainsKey(isbnKey))
            {
                groupedRecords[publisherKey][isbnKey] = (record.Price, record.Stock);
            }
            else
            {
                var existing = groupedRecords[publisherKey][isbnKey];
                if (existing.Price != record.Price || existing.Stock != record.Stock)
                {
                    discrepancies.Add(new Discrepancy
                    {
                        LineNumber = record.LineNumber,
                        Publisher = record.PublisherName,
                        Title = record.Title
                    });
                }
            }
        }

        WriteDiscrepancies(discrepancies);
    }
    catch(OperationCanceledException)
    {
        throw;
    }
    catch(Exception ex)
    {
        throw;
    }
}

2. 在MainForm中正确调用btnClick #

在MainForm的Submit按钮点击事件中，传递当前实例给Books的btnClick方法：

// MainForm.cs
private async void btnSubmit_Click(object sender, EventArgs e)
{
    Books booksHandler = new Books();
    await booksHandler.btnClick(this); // 传递当前主窗口实例
}

3. 确保FormClosing事件正确绑定 #

检查MainForm的构造函数，确保FormClosing事件已绑定：

// MainForm.cs构造函数
public MainForm()
{
    InitializeComponent();
    this.FormClosing += MainForm_FormClosing; // 手动绑定事件（如果设计器未绑定）
}

4. 优化FormClosing提示逻辑（可选） #

添加提示告知用户无法关闭的原因：

// MainForm.cs
private void MainForm_FormClosing(object sender, FormClosingEventArgs e)
{
    if (isProcessing)
    {
        e.Cancel = true;
        MessageBox.Show("当前正在处理任务，无法关闭窗口！");
    }
}

额外注意事项 #

• 确保TxtBox控件可被访问：可以将MainForm中TxtBox的Modifiers属性设为Public，或添加公开属性获取路径：

  // MainForm.cs
  public string ExcelPath => TxtBox.Text;
  

  之后在Books.cs中使用mainForm.ExcelPath获取路径。

内容的提问来源于stack exchange，提问作者Anonymous