DataGridView打印预览丢失首行问题求助

问题说明 #

为DataGridView实现打印预览功能后，代码整体可运行，但打印内容始终丢失ID为1的行，从ID为2的行开始输出。

问题原因 #

原代码的newpage逻辑错误：首次进入循环时newpage=True，此时仅绘制了表头文本，未绘制第一行的单元格内容；循环结束后newpage设为False，mRow自增到1，导致后续直接从第二行开始绘制内容。

修复后的代码 #

Private Sub PrintDocument1_PrintPage(sender As System.Object, e As System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage

    Dim mRow As Integer = 0
    Dim newpage As Boolean = True
    PrintDocument1.DefaultPageSettings.Landscape = True

    With DataGridView1
        Dim fmt As StringFormat = New StringFormat(StringFormatFlags.LineLimit)
        fmt.LineAlignment = StringAlignment.Center
        fmt.Trimming = StringTrimming.EllipsisCharacter
        Dim y As Single = e.MarginBounds.Top

        ' 新页面顶部单独绘制表头
        If newpage Then
            Dim xHeader As Single = e.MarginBounds.Left
            Dim hHeader As Single = 0
            For Each col As DataGridViewColumn In .Columns
                Dim rcHeader As RectangleF = New RectangleF(xHeader, y, col.Width, .RowTemplate.Height)
                e.Graphics.DrawRectangle(Pens.Black, rcHeader.Left, rcHeader.Top, rcHeader.Width, rcHeader.Height)
                e.Graphics.DrawString(col.HeaderText, .Font, Brushes.Black, rcHeader, fmt)
                xHeader += rcHeader.Width
                hHeader = Math.Max(hHeader, rcHeader.Height)
            Next
            y += hHeader
            newpage = False
        End If

        ' 逐行绘制表格内容（包含首行）
        Do While mRow < .RowCount
            Dim row As DataGridViewRow = .Rows(mRow)
            Dim x As Single = e.MarginBounds.Left
            Dim h As Single = 0
            For Each cell As DataGridViewCell In row.Cells
                Dim rc As RectangleF = New RectangleF(x, y, cell.Size.Width, cell.Size.Height)
                e.Graphics.DrawRectangle(Pens.Black, rc.Left, rc.Top, rc.Width, rc.Height)
                e.Graphics.DrawString(row.Cells(cell.ColumnIndex).FormattedValue.ToString(), .Font, Brushes.Black, rc, fmt)
                x += rc.Width
                h = Math.Max(h, rc.Height)
            Next
            y += h
            mRow += 1
            ' 判断是否需要分页
            If y + .RowTemplate.Height > e.MarginBounds.Bottom Then
                e.HasMorePages = True
                newpage = True
                Exit Sub
            End If
        Loop
        e.HasMorePages = False
    End With
End Sub

修复要点 #

1. 表头绘制逻辑独立：仅在新页面开始时绘制表头，绘制完成后直接下移坐标，不占用首行的绘制位置。
2. 行内容无差别绘制：移除原代码中newpage对行内容的判断，确保首行（ID=1）能正常输出。
3. 优化分页判断：使用行模板高度预估下一行位置，避免计算误差导致的分页异常。
4. 明确结束标记：循环结束后设置e.HasMorePages = False，确保打印流程正常收尾。

内容的提问来源于stack exchange，提问作者Salwa Hamim