多选AspxListBox后仅加载最后项数据？AspxGridView循环取数问题

问题原因 #

你的代码存在两个核心问题导致多选时只显示最后一项数据：

1. 多次绑定GridView：循环处理每个选中项时，每次执行SQL后立刻将DataTable绑定到GridView，后面的绑定会直接覆盖前面的结果。
2. DataTable数据被覆盖：如果FillDataTable方法是清空现有DataTable再填充新数据，那么每次查询都会清除之前的结果，最终只剩最后一项的数据。

推荐解决方案：一次性查询所有选中项（性能更优） #

通过收集所有选中项，构建带参数的IN查询，一次性从数据库获取所有数据，最后统一绑定到GridView，减少数据库交互次数。

Protected Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
    Dim dt As New DataTable
    Dim myconn As New clsConnection
    Dim selectedItems As New List(Of String)

    ' 收集所有选中项的文本
    For Each item As ListEditItem In lBoxItem.Items
        If item.Selected Then
            selectedItems.Add(item.Text)
        End If
    Next

    ' 如果没有选中项，清空GridView
    If selectedItems.Count = 0 Then
        grdViewItems.DataSource = Nothing
        grdViewItems.DataBind()
        Return
    End If

    ' 构建带参数的IN查询语句
    Dim paramPlaceholders As String = String.Join(", ", selectedItems.Select(Function(i, idx) $"@Item{idx}"))
    Dim strSelect As String = $"SELECT ID, Description, Qty, Remark FROM table_1 WHERE itemString IN ({paramPlaceholders})"

    ' 为每个选中项添加对应参数
    For idx As Integer = 0 To selectedItems.Count - 1
        myconn.AddParameter($"@Item{idx}", MySqlDbType.String)
        myconn.SetParameter($"@Item{idx}", selectedItems(idx))
    Next

    Try
        myconn.OpenConnection()
        myconn.FillDataTable(dt, strSelect)
        ' 统一绑定所有数据到GridView
        grdViewItems.DataSource = dt
        grdViewItems.DataBind()
    Catch ex As Exception
        ' 可添加异常日志记录逻辑
    Finally
        myconn.CloseConnection()
        myconn.ClearAllParameter()
    End Try
End Sub

备选解决方案：循环累加数据（适合需逐个处理选中项的场景） #

如果必须逐个查询每个选中项，可通过临时DataTable存储单次查询结果，合并到主DataTable后，最后统一绑定。

Protected Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
    Dim dt As New DataTable
    Dim myconn As New clsConnection

    For Each item As ListEditItem In lBoxItem.Items
        If item.Selected Then
            Dim strItem As String = item.Text
            Dim strSelect As String = "SELECT ID, Description, Qty, Remark FROM table_1 WHERE itemString = @ItemString"
            
            myconn.AddParameter("@ItemString", MySqlDbType.String)
            myconn.SetParameter("@ItemString", strItem)

            Try
                myconn.OpenConnection()
                Dim tempDt As New DataTable
                myconn.FillDataTable(tempDt, strSelect)
                ' 将单次查询结果合并到主DataTable
                If tempDt.Rows.Count > 0 Then
                    dt.Merge(tempDt)
                End If
            Catch ex As Exception
                ' 异常处理逻辑
            Finally
                myconn.CloseConnection()
                myconn.ClearAllParameter()
            End Try
        End If
    Next

    ' 循环结束后统一绑定数据
    If dt.Rows.Count > 0 Then
        grdViewItems.DataSource = dt
        grdViewItems.DataBind()
    Else
        grdViewItems.DataSource = Nothing
        grdViewItems.DataBind()
    End If
End Sub

内容的提问来源于stack exchange，提问作者Newbie