Question

我目前正在使用VB.NET express for desktop，2013。我很难将SQL数据绑定到带有数组的循环上的某些datagridviews。我收到一个对象null错误，因为在直接投射线上它没有拉动datagridview。我在选项卡控件工具上有多个datagridviews，每个选项卡有一个datagridview。这是我的代码：

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:interpolator="@android:anim/linear_interpolator">

    <scale
        android:duration="700"
        android:fillBefore="false"
        android:fromXScale="1.0"
        android:fromYScale="1.0"
        android:toXScale="0.0"
        android:toYScale="0.0" />
</set>

错误在线

 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

但是在

之前，空错误不会触发

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

Answer 1

尝试使用DataGridView列表，如下所示：

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控件位于其他选项卡上，则它们不在Me.Controls中。因为你知道这个名字，所以你可以迭代它们的数组，而不是将它们捕获并抛出它们。您也不需要为每个都创建新连接，也不需要为每个数据表创建重复的数据表：

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其他网格中所做的更改，则您只需要8个相同的DataTable。为此，请在同一连接上使用数据集来创建表：

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null错误

2 个答案: