Direct Cast 为 datagridview 提供空错误

Question

我目前在 VB.NET 桌面版 express 工作，2013 年。我很难将 SQL 数据绑定到数组循环中的某些数据网格视图。我收到一个对象空错误，这是因为在直接投射线上它没有拉 datagridview。我在选项卡控件工具上有多个数据网格视图，每个选项卡一个数据网格视图。这是我的代码：

 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

错误在线

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

但是空错误直到

才会触发

  RelativeDGV.DataSource = dt

Answer 1

尝试像这样使用 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

如果各种 DGV 控件在其他选项卡上，则它们不会在 Me.Controls 中。与其将它们捞出并扔掉，不如迭代它们的数组，因为您知道它们的名称。您也不需要为每个创建新连接，也不需要为每个创建重复的数据表：

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

如果您不希望每个网格自动反映在其他网格中所做的更改，您只需要 8 个相同的数据表。为此，使用同一连接上的数据集来创建表：

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

Direct Cast 为 datagridview 提供空错误

Direct Cast giving null error for datagridview

vb.net

arrays

datagridview

directcast