直接強制轉換為datagridview提供空錯誤

Question

我目前正在2013年面向台式機的VB.NET Express中工作。我很難將SQL數據綁定到具有數組的循環上的某些datagridviews。 我收到一個對象為null的錯誤，這是因為在直接投射線上沒有拉出datagridview。 我在一個標簽頁控制工具上有多個datagridviews，每個標簽頁一個datagridview。 這是我的代碼：

 try
 Dim array() As Integer = {"2", "3", "4", "7", "8", "10", "11", "12"}

        For Each value As Integer In array
            Dim RelativeDGV = DirectCast(Me.Controls("DataGridLine" & value), DataGridView)
            Using conn1 As New SqlConnection(connstring)
                conn1.Open()
                Using comm1 As New SqlCommand("SELECT LineNumber FROM tableA where LineNumber = @LineNumber", conn1)
                    comm1.Parameters.AddWithValue("@LineNumber", value)
                    Dim dt As New DataTable
                    Dim sql As New SqlDataAdapter(comm1)
                    sql.Fill(dt)
                   RelativeDGV.DataSource = dt
                End Using
                conn1.Close()
            End Using 
        Next

    Catch ex As Exception
        MsgBox(ex.ToString)
    End Try

錯誤在線

 Dim RelativeDGV = DirectCast(Me.Controls("DataGridLine" & value), DataGridView)

但是直到出現空錯誤才觸發

  RelativeDGV.DataSource = dt

Answer 1

嘗試像這樣使用DataGridView列表：

Try
    Dim array() As DataGridView = {DataGridLine2, DataGridLine3, DataGridLine4, DataGridLine7, DataGridLine8, DataGridLine10, DataGridLine11, DataGridLine12}
    For Each RelativeDGV As DataGridView In array
        Dim value As Integer = Regex.Replace(RelativeDGV.Name, "[^0-9]+", String.Empty)
        'or like this
        'Dim value As Integer = RelativeDGV.Name.Substring(12, RelativeDGV.Name.Length - 12)
        Using conn1 As New SqlConnection(connstring)
            conn1.Open()
            Using comm1 As New SqlCommand("SELECT LineNumber FROM tableA where LineNumber = @LineNumber", conn1)
                comm1.Parameters.AddWithValue("@LineNumber", value)
                Dim dt As New DataTable
                Dim sql As New SqlDataAdapter(comm1)
                sql.Fill(dt)
                RelativeDGV.DataSource = dt
            End Using
            conn1.Close()
        End Using
    Next

Catch ex As Exception
    MsgBox(ex.ToString)
End Try

Answer 2

如果各種DGV控件在其他選項卡上，則它們將Me.Controls 。 因為知道名稱，所以您可以迭代它們的數組，而不必將它們扔掉並拋棄它們。 您也不需要為每個連接創建新連接，也不需要為每個連接創建重復的數據表：

Dim dgvCtrls As DataGridView() = {DataGridLine2, DataGridLine3, DataGridLine4}

Using conn1 As New SqlConnection(connstring)
    conn1.Open()
    Using comm1 As New SqlCommand("SELECT LineNumber FROM...", conn1)
        '    ...
        dt.Load(comm1.ExecuteReader())
    End Using

    conn1.Close()
End Using

For Each dgv In dgvCtrls
    dgv.DataSource = dt
Next

如果您不希望每個網格自動反映其他網格所做的更改，則只需要8個相同的DataTable。 為此，請在同一連接上使用數據集來創建表：

Dim SQL = "..."
Dim dgvCtrls As DataGridView() = {dgv5, dgv2, dgv3,...}
Dim ds = New DataSet

Using dbcon As New SqlConnection(SQLConnStr)
    Using cmd As New SqlCommand(SQL, dbcon)
        dbcon.Open()
        For n As Int32 = 0 To dgvCtrls.Count - 1
            ds.Load(cmd.ExecuteReader, LoadOption.OverwriteChanges, dgvCtrls(n).Name)
        Next
    End Using
End Using

For Each dgv In dgvCtrls
    dgv.DataSource = ds.Tables(dgv.Name)
Next