店铺收银系统收据打印异常：提示无页面如何排查？

核心故障原因 #

1. 打印预览对话框未关联打印文档
   printPreviewDialog1没有绑定printDocument1，导致预览窗口无法获取要渲染的打印内容，这是直接触发“未找到页面”提示的原因。
2. PrintPage方法内过早清空数据
   在预览阶段（用户未确认打印）就执行datafrmcheckout.Rows.Clear()，会直接清除预览依赖的数据，导致预览无内容，同时后续真实打印也会丢失数据。
3. 类级变量pos的状态污染
   pos作为类级变量，每次打印后被重置为100，下次打印时内容会从页面下方开始绘制，可能超出可视区域，导致预览无内容。

修复后的代码示例 #

private void printDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
{
    // 将pos改为方法内局部变量，避免多次打印的状态残留
    int pos = 60;
    e.Graphics.DrawString("The Androids Dungeon", new Font("Century Gothic", 12, FontStyle.Bold), Brushes.Red, new Point(80));
    e.Graphics.DrawString("ID Product Price Quantity Total", new Font("Century Gothic", 10, FontStyle.Bold), Brushes.Red, new Point(26,40));
    
    // 先复制数据，避免原集合在遍历中被修改
    var rows = datafrmcheckout.Rows.Cast<DataGridViewRow>().ToList();
    foreach(DataGridViewRow row in rows)
    {
        // 跳过DataGridView自动生成的空行
        if (row.IsNewRow) continue;
        
        int shopitemid = Convert.ToInt32(row.Cells["Column1"].Value);
        string shopname = row.Cells["Column2"].Value?.ToString() ?? "";
        int shopprice = Convert.ToInt32(row.Cells["Column3"].Value);
        int shopquantity = Convert.ToInt32(row.Cells["Column4"].Value);
        int shoptotal = Convert.ToInt32(row.Cells["Column5"].Value);
        
        e.Graphics.DrawString(shopitemid.ToString(), new Font("Century Gothic", 8, FontStyle.Bold), Brushes.Blue, new Point(26, pos));
        e.Graphics.DrawString(shopname, new Font("Century Gothic", 8, FontStyle.Bold), Brushes.Blue, new Point(45, pos));
        e.Graphics.DrawString(shopprice.ToString(), new Font("Century Gothic", 8, FontStyle.Bold), Brushes.Blue, new Point(120, pos));
        e.Graphics.DrawString(shopquantity.ToString(), new Font("Century Gothic", 8, FontStyle.Bold), Brushes.Blue, new Point(170, pos));
        e.Graphics.DrawString(shoptotal.ToString(), new Font("Century Gothic", 8, FontStyle.Bold), Brushes.Blue, new Point(235, pos));
        pos += 20;
    }
    
    e.Graphics.DrawString($"Grand Total: £ {grdtotal}", new Font("Century Gothic", 12, FontStyle.Bold), Brushes.Crimson, new Point(60, pos + 50));
    e.Graphics.DrawString("***The Android Dungeon***", new Font("Century Gothic", 12, FontStyle.Bold), Brushes.Crimson, new Point(40, pos + 85));
}

private void Printbt_Click(object sender, EventArgs e)
{
    // 关键：绑定打印文档到预览对话框
    printPreviewDialog1.Document = printDocument1;
    printDocument1.DefaultPageSettings.PaperSize = new System.Drawing.Printing.PaperSize("pprnm", 285, 600);
    
    if(printPreviewDialog1.ShowDialog() == DialogResult.OK)
    {
        // 用户确认打印后再清空数据
        datafrmcheckout.Rows.Clear();
        datafrmcheckout.Refresh();
        grdtotal = 0;
        printDocument1.Print();
    }
}

额外优化点 #

• 增加row.IsNewRow判断，避免处理DataGridView自动添加的空行
• 使用?.ToString() ?? ""处理单元格值为null的情况，防止空引用异常
• 延迟数据清空操作到用户确认打印后，保证预览与打印的数据一致性

内容的提问来源于stack exchange，提问作者jacksonb