Question

我目前在表单中有两个ComboBox。 ComboBox A用于选择某个项目。 ComboBox B将填充4个特定于ComboBox A中所做选择的项目。我能够完成所有这些工作。

我的问题是：如果我在ComboBox A中进行选择，ComboBox B将填充特定于我在ComboBox A中所做选择的4个项目。但是如果我在ComboBox A中进行另一个选择，则项目不会覆盖以前在ComboBox B中填充的项目，它们只是添加到已填充的项目中。

我的问题是，当在ComboBox A中进行新选择时，有没有在ComboBox B中覆盖以前的项目？

Imports MySql.Data.MySqlClient
Public Class Form2
Dim MySqlConn As MySqlConnection
Dim COMMAND As MySqlCommand
Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    MySqlConn = New MySqlConnection
    MySqlConn.ConnectionString = "server=localhost;userid=root;password=root;database=test"
    Dim READER As MySqlDataReader
    Try
        MySqlConn.Open()
        Dim Query As String
        Query = "select * from test.boxinformation"
        COMMAND = New MySqlCommand(Query, MySqlConn)
        READER = COMMAND.ExecuteReader
        While READER.Read
            Dim boxSN = READER.GetString("Box_SN")
            ComboBox_Box.Items.Add(boxSN)
        End While
        MySqlConn.Close()
    Catch ex As MySqlException
        MessageBox.Show(ex.Message)
    Finally
        MySqlConn.Dispose()
    End Try
End Sub
Private Sub ComboBox_STSBox_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox_Box.SelectedIndexChanged
    MySqlConn = New MySqlConnection
    MySqlConn.ConnectionString = "server=localhost;userid=root;password=root;database=test"
    Dim READER As MySqlDataReader
    Try
        MySqlConn.Open()
        Dim Query As String
        Query = "select * from test.boxinformation where Box_SN='" & ComboBox_Box.Text & "'"
        COMMAND = New MySqlCommand(Query, MySqlConn)
        READER = COMMAND.ExecuteReader
        While READER.Read
            ComboBox_Port.Items.Add(READER.GetString("1_IP"))
            ComboBox_Port.Items.Add(READER.GetString("2_IP"))
            ComboBox_Port.Items.Add(READER.GetString("3_IP"))
            ComboBox_Port.Items.Add(READER.GetString("4_IP"))
        End While
        MySqlConn.Close()
    Catch ex As MySqlException
        MessageBox.Show(ex.Message)
    Finally
        MySqlConn.Dispose()
    End Try
End Sub

结束班

Answer 1

如果您添加新项目而不先删除旧项目，那么这将是预期的行为。要在添加新集合之前从组合框中删除所有项目，您需要清除其objectCollection，如下所示;

ComboBoxA.ObjectCollection.Clear()
'now add your new set of items...

Answer 2

为了让你以前的值使用ComboBox_Port.Clear的ComboBox，把它放在你的行之后

READER = COMMAND.ExecuteReader

所以你的代码将是：

READER = COMMAND.ExecuteReader
' *** drop your new line here ***
ComboBox_Port.Clear
While READER.Read
    ComboBox_Port.Items.Add(READER.GetString("1_IP"))
    ComboBox_Port.Items.Add(READER.GetString("2_IP"))
    ComboBox_Port.Items.Add(READER.GetString("3_IP"))
    ComboBox_Port.Items.Add(READER.GetString("4_IP"))
End While

覆盖以前的组合框选择？

2 个答案: