Question

我已经阅读了很多论坛。实际上，他们都没有回答我的问题。第二次运行该过程时会触发此问题。我第一次运行程序时没有问题

我从主菜单调用windows窗体：

Private Sub ProjectsToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles ProjectsToolStripMenuItem.Click
    SqlStatement1 = "Select TOP(1) fiscalyear From " & ConfigTable & " Order By fiscalyear DESC"
    FiscalYear = GetData(SqlStatement1, 0)
    frmCPProjectInfo.ShowDialog()
End Sub

表单的frmCPProjectInfo在sub：

之后加载事件调用

    SqlStatement = "Select p.projtitle, p.projectid, d.deptid, p.deptrank, p.account, SUBSTRING(p.account, 6, 4) As last4 From (Select dept01.*, f.funddesc, f.fund_num From (Select * From "
    SqlStatement &= DepartmentsTable & " Where deptid In (Select deptid From " & WorkAreaTable & " Where userlogin = '" & CurrentUser & "')) dept01 LEFT OUTER JOIN " & FundsTable
    SqlStatement &= " f On dept01.fund = f.fund) d LEFT OUTER JOIN " & ProjectInfoTable & " p On p.deptid = d.deptid Where p.FiscalYear = " & FiscalYear & " Order by deptid, projectid"
    frmCPSelectProject.ShowDialog()
    LoadAll()
    cmdDeleteProject.Image = ListOfImages.Images(0)
    ToolTip1.SetToolTip(cmdDeleteProject, "Delete Project")

在这里，LoadAll（）显示项目。

在表格frmCPSelectProject下面加载事件调用sub：

  Sub DisplayAll()
    Dim sqlConn As New SqlConnection(connStringCIP)
    Dim sqlCom As New SqlCommand
    Dim drCIP As SqlDataReader
    Dim dtCIP As DataTable = New DataTable

    sqlConn.Open()
    sqlCom = New SqlCommand(SqlStatement, sqlConn)
    drCIP = sqlCom.ExecuteReader()
    DataGridView1.DataSource = ""
    dtCIP.Load(drCIP)
    If dtCIP.Rows.Count = 0 Then
        MessageBox.Show("There is no record to show")
        NoRec = True
        dtCIP.Dispose()
        drCIP.Dispose()
        sqlCom.Dispose()
        sqlConn.Close()
        sqlConn.Dispose()
        Me.Close()
        Exit Sub
    End If
    DataGridView1.DataSource = dtCIP
    DataGridView1.Columns(0).Width = 300
    DataGridView1.Columns(1).Width = 85
    DataGridView1.Columns(2).Width = 85
    DataGridView1.Columns(3).Width = 85
    DataGridView1.Columns(4).Width = 140
    DataGridView1.Columns(5).Width = 250

    dtCIP.Dispose()
    drCIP.Dispose()
    sqlCom.Dispose()
    sqlConn.Close()
    sqlConn.Dispose()
End Sub

然后，我选择项目执行以下例程：

Private Sub cmdContinue_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdContinue.Click
    SelectID(DataGridView1.CurrentCell.RowIndex)
End Sub

Sub SelectID(ByVal NewInd)
    Dim DeptID As String
    Dim DeptRank As String

    ProjectID = DataGridView1.Rows(RowInd).Cells(1).Value
    DeptID = Trim(Str(DataGridView1.Rows(RowInd).Cells(2).Value))
    DeptRank = Trim(Str(DataGridView1.Rows(RowInd).Cells(3).Value))
    Select Case Order
        Case "projtitle"
            SearchBy = "projtitle"
            SearchItem = DataGridView1.Rows(RowInd).Cells(0).Value
        Case "account"
            SearchBy = "account"
            SearchItem = DataGridView1.Rows(RowInd).Cells(4).Value
    End Select

    Me.Close()
End Sub

之后，例程LoadAll（）（见上文）执行。

问题是，如果我关闭表格frmCPProjectInfo返回主菜单然后再次运行该过程，我收到一条错误消息：

未处理的类型＆＃39; System.NullReferenceException＆＃39;发生在System.Windows.Forms.dll中附加信息：对象引用未设置为对象的实例。

程序停在线上 DataGridView1.Columns（0）.Width = 300（参见上面的DisplayAll（））。有人能帮助我吗？提前致谢

使用datagridview在vb.net中工作时出现错误消息

0 个答案: