指示具有特定 ID 的组合框值？

Question

我制作了一个 Sub，它将用贷款描述填充我的组合框。我想在 selectedindexchanged 上获取 loandescription 的 loancode 而无需再次查询数据库。这可能吗？或者我应该查询数据库以获取指示的 loancode?

Private Sub LoanProducts()
    Using cmd As New SqlClient.SqlCommand("SELECT loancode,loandescription FROM LoanProducts", gSQlConn)
        Dim dt As New DataTable
        Dim da As New SqlClient.SqlDataAdapter
        dt.Clear()
        da.SelectCommand = cmd
        da.Fill(dt)
        For Each row As DataRow In dt.Rows
            CmbLoanAvail.Items.Add(row("loandescription"))
        Next row
    End Using
End Sub

预期输出：

每次组合框索引发生变化时，所选贷款描述的贷款代码将显示在文本框中。

Answer 1

如果您可以获得强类型 classes 的数据库行，您可以使用 ItemSource、DisplayMember 和 ValueMember，这将解决您的问题。

如果您提出，您可以使用 SelectedIndex 属性或 ComboBox。此外，您需要将结果集存储在某些 class 字段中（最好是 Pirvate 一个）。请参阅下面的示例代码：

Public Class Form4
    Private _result As DataTable

    Private Sub Form4_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim dt As New DataTable
        dt.Columns.Add("col1")
        dt.Columns.Add("col2")
        dt.Rows.Add("val11", "val12")
        dt.Rows.Add("val21", "val22")
        ' at this point, we got our result from DB
        _result = dt

        For Each row As DataRow In dt.Rows
            ComboBox1.Items.Add(row("col1"))
        Next
    End Sub

    Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
        Dim selectedIndex = ComboBox1.SelectedIndex
        Dim selectedRow = _result(selectedIndex)
    End Sub
End Class

Answer 2

将 DataTable 设置为组合框 .DataSource 属性并使用相应的列名称填充 .ValueMember 和 .DisplayMember 属性。

Private Sub LoanProducts()
    Dim query As String = "SELECT loancode, loandescription FROM LoanProducts"
    Using command As New SqlCommand(query, gSQlConn)
        Dim data As New DataTable
        Dim adapter As New SqlClient.SqlDataAdapter With
        {
            .SelectCommand = cmd
        }

        adapter.Fill(data)

        CmbLoanAvail.ValueMember = "loancode"
        CmbLoanAvail.DisplayMember = "loandescription"
        CmbLoanAvail.DataSource = data
    End Using
End Sub

当用户做出选择

时，您可以使用SelectionChangeCommitted事件执行某些操作

Private Sub comboBox1_SelectionChangeCommitted(
    ByVal sender As Object, ByVal e As EventArgs) Handles comboBox1.SelectionChangeCommitted

    Dim combobox As ComboBox = DirectCast(sender, ComboBox)

    Dim selectedCode As String = combobox.SelectedValue.ToString()  // returns 'loancode'
End Sub

Answer 3

将您的数据库对象保存在使用它们的方法中，这样您就可以确保它们被关闭和处置。请注意第一行 Using 末尾的逗号。这包括同一 Using 块中的命令。

在 Using 块之后设置 DataSource、DisplayMember 和 ValueMember，这样用户界面代码就不会运行，直到连接被释放。

要获取贷款代码，您只需访问 ComboBox 的 SelectValue。

Private Sub LoanProducts()
    Dim dt As New DataTable
    Using gSqlConn As New SqlConnection("Your connection string"),
            cmd As New SqlClient.SqlCommand("SELECT loancode,loandescription FROM LoanProducts", gSqlConn)
        gSqlConn.Open()
        dt.Load(cmd.ExecuteReader)
    End Using
    ComboBox1.DataSource = dt
    ComboBox1.DisplayMember = "loandescription"
    ComboBox1.ValueMember = "loancode"
End Sub

Private Sub ComboBox1_SelectionChangeCommitted(ByVal sender As Object, ByVal e As EventArgs) Handles ComboBox1.SelectionChangeCommitted
    MessageBox.Show($"The Loan Code is {ComboBox1.SelectedValue}")
End Sub

指示具有特定 ID 的组合框值？

Indicate combobox values with a specific ids?

vb.net

combobox

winforms