如何在 vb .net 中刷新组合框项目

Question

如何在 vb .net 中刷新组合框项目

Answer 1

如果您正在谈论 WinForm 上的组合框，该组合框已使用数据源属性分配给对象列表，我发现您必须使数据源设置无效，并在每次列表更改时重新分配它。

即

  attendanceDataFiles.DataSource = Nothing
  attendanceDataFiles.DataSource = myFileList.files
  attendanceDataFiles.DisplayMember = "displayName"
  attendanceDataFiles.ValueMember = "fileName"

Answer 2

如果组合框的内容来自 MySql 数据库，这是刷新组合框项目的另一种方法。您可以在查询中自定义结果。

        comboboxname.Items.clear() 'empty combo box content first

        query = "select code, description from tbl_mode_of_payment where cat = 'LICENSE'" 'mysql query that retrieves payment code and its description based on category
        cmd = New MySqlCommand(query, con)
        reader = cmd.ExecuteReader()

        While reader.Read
            comboboxname.Items.Add(reader.GetString("code") + " - " + reader.GetString("description"))  'add results into the combo box
        End While
        con.Close()

Answer 3

Textbox1.Item.Clear() 然后 调用.item_tb()

Answer 4

在另一个表单将新项目添加到数据库表中后，我必须刷新组合框。我还为组合框使用数据源。这就是我所做的，效果很好。

 Dim cmd As New OleDbCommand()
 Dim dt_Institutions As DataTable

 '~~ The connection is a public OleDbConnection at the head of the form class 
 cmd.Connection = conn
 conn.Open()

 '~~ The control already has been assigned a datasource.  Instead of creating
 '   new one, I reuse the old one.  It must first be cleared of the old data
 dt_Institutions = cb_Institutions.DataSource
 dt_Institutions.Clear()

 cmd.CommandText = "SELECT Institutions.InstitutionID, " &
                   "       Institutions.Institution " &
                   "  FROM Institutions " &
                   " ORDER BY Institutions.Institution"
 
 '~~ While this is not necessary, if you have a large amount of data beging 
 '   filled in, the combobox control will want to sort and organize it with
 '   each add.  This prevents that from happening (and speeding up the code)
 dt_Institutions.BeginLoadData()

 '~~ Looping through the data from the SELECT statement and filling up the
 '   the recycled dataset
 Using rdr As OleDbDataReader = cmd.ExecuteReader()
     While rdr.Read()
         dt_Institutions.Rows.Add({rdr("InstitutionID"), rdr("Institution").ToString})
     End While
 End Using

 '~~ Let the combobox take back over and organize itself only after all the
 '   data has been retrieved
 dt_Institutions.EndLoadData()

 cb_Institutions.SelectedIndex = -1

 conn.Close()

我已将其与 MS-Access 数据库一起使用，并在 VS 2022 中进行编码。该过程是从添加了新记录（在本例中为新机构）的另一个表单中调用的。