vb.net - 引入登录表单后未填写组合框

Question

我的UC_Menu_Scout类中包含以下代码:

Private Sub cmbScoutName_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbScoutName.SelectedIndexChanged

        If loaded = True Then
            cmbReportDate.DataSource = Nothing
            cmbReportDate.DataSource = frmPlayerInfo.filterReports()
            cmbReportDate.DisplayMember = "ReportDate"
            cmbReportDate.ValueMember = "ReportID"
        End If

    End Sub

    Private Sub cmbReportDate_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbReportDate.SelectedIndexChanged

        If loaded = True Then
            If cmbReportDate.Items.Count > 0 Then
                'frmPlayerInfo.myDataTable = Nothing
                frmPlayerInfo.myDataTable = frmPlayerInfo.retrieveDT() 
                dgPlayers.DataSource = frmPlayerInfo.myDataTable
                frmPlayerInfo.setReport()
            End If

        End If

    End Sub

我的frmPlayerInfo类中的以下代码(仅是相关代码):

Public myDataTable As DataTable = Nothing

    Private Sub frmPlayerInfo_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        UC_Menu_Scout1.cmbScoutName.DataSource = retrieveScouts()
        UC_Menu_Scout1.cmbScoutName.DisplayMember = "ScoutName"
        UC_Menu_Scout1.cmbScoutName.ValueMember = "ScoutID"

        UC_Menu_Scout1.cmbReportDate.DataSource = filterReports()
        UC_Menu_Scout1.cmbReportDate.DisplayMember = "ReportDate"
        UC_Menu_Scout1.cmbReportDate.ValueMember = "ReportID"

        myDataTable = retrieveDT()
        UC_Menu_Scout1.dgPlayers.DataSource = myDataTable

        setReport()
        loaded = True
    End Sub

Public Function retrieveDT() As DataTable
        Dim Str As String = _
       <String> SELECT                 
                    Player.PlayerID,
                    PlayerFirstName,
                    PlayerLastName,
                    DOB,
                    Age,
                    PlaceOfBirth,
                    PlayerImage
                FROM 
                    Player
                INNER JOIN 
                    Report ON Report.PlayerID = Player.PlayerID
                /*WHERE 
                    ReportID = @ReportID*/
                ORDER BY 
                    PlayerFirstName     
       </String>

        Dim dt As New DataTable
        Using conn As New SqlClient.SqlConnection(DBConnection)
            conn.Open()
            Using cmdQuery As New SqlClient.SqlCommand(Str, conn)
                cmdQuery.Parameters.Add("@ReportID", SqlDbType.Int).Value = UC_Menu_Scout1.cmbReportDate.SelectedItem.ReportID
                cmdQuery.CommandTimeout = 600

                Try
                    Using daResults As New SqlClient.SqlDataAdapter(cmdQuery)
                        daResults.Fill(dt)
                    End Using
                Catch ex As Exception
                    MsgBox("An Exception has happened: " & ex.Message & vbNewLine)
                End Try

            End Using 'Automatically closes connection
        End Using

        Return dt

    End Function

在创建登录表单之前，一切正常。从那时起(成功登录后)，我的组合框一直收到“对象变量或未设置块变量的错误”错误-表示在表单加载事件时它们现在为空。由于设置了“已加载” bool(boolean) 值，因此消除了frmPlayerInfo.filterReports()的错误，但是我仍然在此行cmdQuery.Parameters.Add(“@ ReportID”，SqlDbType.Int上收到针对frmPlayerInfo.retrieveDT-的相同消息。 )。值= UC_Menu_Scout1.cmbReportDate.SelectedItem.ReportID。再次说明组合框(cmbReportDate)为空。

初始加载事件起作用，但是崩溃发生在cmbReportDate_SelectedIndexChanged事件上，在以下行上:restoreDT函数中的frmPlayerInfo.myDataTable = frmPlayerInfo.retrieveDT()。

如果我删除登录表单，则不会出现此类问题-特定于我程序的答案将不胜感激。

Answer 1

这是一个如何从UserControl中获取对主窗体的引用的示例:

    Dim frm As Form = Me.FindForm
    If TypeOf frm Is frmPlayerInfo Then
        Dim player As frmPlayerInfo = DirectCast(frm, frmPlayerInfo)
        ' ... now do something with "player" ...

    End If

不，这是 而不是一个好的设计，因为现在您的UserControl只能与frmPlayerInfo表单一起使用。如果您对此表示满意，那么以下是使用您的特定代码的示例:

Private Sub cmbReportDate_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbReportDate.SelectedIndexChanged
    If loaded = True Then
        If cmbReportDate.Items.Count > 0 Then
            Dim frm As Form = Me.FindForm
            If TypeOf frm Is frmPlayerInfo Then
                Dim player As frmPlayerInfo = DirectCast(frm, frmPlayerInfo)
                ' ... now do something with "player" ...
                player.myDataTable = player.retrieveDT()
                dgPlayers.DataSource = player.myDataTable
                player.setReport()
            End If
        End If
    End If
End Sub