如何在vb中创建打印按钮 [英] How to create a print button in vb

问题描述

我需要帮助，我正在尝试创建一个按钮，从我的daatagridview打印我的信息。下面是我输入的代码，但是当我尝试它时，它给出一个n错误，错误是。 {对象引用未设置为对象的实例。} NullReferenceException未处理

 私有  Sub  PrintToolStripButton_Click（sender  As   Object ，e  As  EventArgs）句柄 PrintToolStripButton.Click 
 PrintDialog1.ShowDialog（）
 PrintDialog1.Document = PrintDocument1 
 PrintDocument1.DocumentName =  出勤 
 PrintDocument1.Print（）
 结束  Sub  
 
 私人  Sub  PrintDocument1_PrintPage（发件人作为 对象，e  As  Printing.PrintP ageEventArgs）句柄 PrintDocument1.PrintPage 
  Dim  ColumnCount 正如 整数 = AttendanceDataGridView.ColumnCount 
  Dim  RowCount 作为 整数 = AttendanceDataGridView.RowCount 
 
  Dim  CellTopPos 作为 整数 = PrintDocument1.PrinterSettings.DefaultPageSettings.Margins.Top 
 
 对于行=  0    RowCount  -  < span class =code-digit> 1  
 
  Dim  CellLeftPos  As  整数 = PrintDocument1.PrinterSettings.DefaultPage Settings.Margins.Left 
 
 对于 Cell =  0  至 ColumnCount  -   1  
 
  Dim  CellValue  As   String  = AttendanceDataGridView.Rows（Row）.Cells（Cell）.Value.ToString（）
  Dim  CellWidth = AttendanceDataGridView.Rows（Row）.Cells（Cell）.Size.Width +  50  
  Dim  CellHeight = AttendanceDataGridView.Rows（Row）.Cells（Cell）.Size.Height 
 
  Dim  Brush  As  新 SolidBrush（Color.Black）
 e.Graphics.DrawString（CellValue，新字体（  Century Gothic， 10 ），Brush，CellLeftPos，CellTopPos）
 e.Graphics.DrawRectangle（ Pens.Black，CellLeftPos，CellTopPos，CellWidth，CellHeight）
 
 CellLeftPos + = CellWidth 
  Next  
 
 CellTopPos + = AttendanceDataGridView.Rows（Row）.Cells（ 0 ）。Size.Height 
  Next  
 结束  Sub  

解决方案

问题出现了，因为您尝试处理的某个单元格没有值，所以 .Value.ToString（）电话是抛出异常。



为了解决这个问题，只需检查包含某些内容的单元格，然后再尝试使用值。例如

 对于 Cell =  0  至 ColumnCount  -   1  
 
 如果 不 AttendanceDataGridView.Rows（Row）.Cells（Cell）.Value   没有 然后 
  Dim  CellValue 正如  String  = AttendanceDataGridView.Rows（Row）.Cells（Cell）.Value.ToString（）
  Dim  CellWidth = AttendanceDataGridView.Rows（Row）.Cells（Cell）.Size.Width +  50  
  Dim  CellHeight = AttendanceDataGridView.Rows（Row）.Cells（Cell）.Size.Height 
 
  Dim  Brush  As  新 SolidBrush（Color.Black）
 e.Graphics.DrawString（CellValue，新字体（  Century Gothic， 10 ），Brush，CellLeftPos，CellTopPos）
 e.Graphics.DrawRectangle（Pens.Black，CellLeftPos，CellTopPos，CellWidth，CellHeight）
 
 CellLeftPos + = CellWidth 
 结束 如果 
 
 下一步 

hi please i need help on this , i am trying to create a button that will print my information from my daatagridview. below is the code i have inputed but when i try it it give a n error and the error is . {"Object reference not set to an instance of an object."} NullReferenceException unhandled

Private Sub PrintToolStripButton_Click(sender As Object, e As EventArgs) Handles PrintToolStripButton.Click
    PrintDialog1.ShowDialog()
    PrintDialog1.Document = PrintDocument1
    PrintDocument1.DocumentName = "Attendance"
    PrintDocument1.Print()
End Sub

Private Sub PrintDocument1_PrintPage(sender As Object, e As Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage
    Dim ColumnCount As Integer = AttendanceDataGridView.ColumnCount
    Dim RowCount As Integer = AttendanceDataGridView.RowCount

    Dim CellTopPos As Integer = PrintDocument1.PrinterSettings.DefaultPageSettings.Margins.Top

    For Row = 0 To RowCount - 1

        Dim CellLeftPos As Integer = PrintDocument1.PrinterSettings.DefaultPageSettings.Margins.Left

        For Cell = 0 To ColumnCount - 1

            Dim CellValue As String = AttendanceDataGridView.Rows(Row).Cells(Cell).Value.ToString()
            Dim CellWidth = AttendanceDataGridView.Rows(Row).Cells(Cell).Size.Width + 50
            Dim CellHeight = AttendanceDataGridView.Rows(Row).Cells(Cell).Size.Height

            Dim Brush As New SolidBrush(Color.Black)
            e.Graphics.DrawString(CellValue, New Font("Century Gothic", 10), Brush, CellLeftPos, CellTopPos)
            e.Graphics.DrawRectangle(Pens.Black, CellLeftPos, CellTopPos, CellWidth, CellHeight)

            CellLeftPos += CellWidth
        Next

        CellTopPos += AttendanceDataGridView.Rows(Row).Cells(0).Size.Height
    Next
End Sub

解决方案

The problem is occurring because one of the cells you are trying to handle does not have a value so the .Value.ToString() call is throwing an exception.

To get around this just check for the cell containing something before attempting to use the Value. For example

For Cell = 0 To ColumnCount - 1

    If Not AttendanceDataGridView.Rows(Row).Cells(Cell).Value Is Nothing Then
        Dim CellValue As String = AttendanceDataGridView.Rows(Row).Cells(Cell).Value.ToString()
        Dim CellWidth = AttendanceDataGridView.Rows(Row).Cells(Cell).Size.Width + 50
        Dim CellHeight = AttendanceDataGridView.Rows(Row).Cells(Cell).Size.Height

        Dim Brush As New SolidBrush(Color.Black)
        e.Graphics.DrawString(CellValue, New Font("Century Gothic", 10), Brush, CellLeftPos, CellTopPos)
        e.Graphics.DrawRectangle(Pens.Black, CellLeftPos, CellTopPos, CellWidth, CellHeight)

        CellLeftPos += CellWidth
    End If

Next

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