Question

我有以下代码：

    Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.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='" & ComboBox1.Text & "'"
        COMMAND = New MySqlCommand(Query, MySqlConn)
        READER = COMMAND.ExecuteReader
        ComboBox2.Items.Clear()
        While READER.Read
            Dim CP = READER.GetString("CP_IP")
            Dim PC = READER.GetString("PC_IP")
            Dim M1 = READER.GetString("M1_IP")
            Dim M2 = READER.GetString("M2_IP")
            ComboBox2.Items.Add(CP)
            ComboBox2.Items.Add(PC)
            ComboBox2.Items.Add(M1)
            ComboBox2.Items.Add(M2)
        End While

        MySqlConn.Close()
    Catch ex As MySqlException
        MessageBox.Show(ex.Message)
    Finally
        MySqlConn.Dispose()
    End Try
End Sub

基本上，正在发生的事情是我有一个SQL数据库，其中包含特定于组件的IP地址。因此，当用户在ComboBox1中选择Component时，特定于该Component的IP地址将填充在ComboBox2中。

我的数据库设置在一个包含5列的表中。 ComboBox1从名为“Box_SN”的列中提取数据，ComboBox2从名为“CP_IP”，“PC_IP”，“M1_IP”和“M2_IP”的列中提取数据。当用户在ComboBox1中进行选择时，与ComboBox1中所选组件关联的IP地址将显示在ComboBox2中。所以现在有4个IP地址填充在ComboBox2中，这些IP地址特定于ComboBox1中的选定框。所有这一切都按照应有的方式发挥作用。

但我没有在ComboBox2中显示IP地址，而是想显示文本。因此对于“CP_IP”而不是显示其IP地址，我希望它显示“组件A”，而对于“PC_IP”，我希望它显示“组件B”

所以我想我想说的是，我想通过我的数据库将IP地址分配给文本而不仅仅是正在读取的IP。

如果有人能帮助我，我会非常感激。

Answer 1

在网络上，html B(int x, int y = 0) : A(y) { b=x;cout<<b; cout<<"B Constructor\n"; }元素包含内容和值的选项。在Windows窗体中，ComboBox元素只有select。只使用字符串对象是很常见的。

但是

只要Objects方法产生有意义的东西，您就可以在其中放置任何类型的对象。这些，例如：

.ToString()

然后，还花时间修复大量SQL注入问题，原始方法如下所示：

Public Class ComboItem(Of T)
    Public Property Name As String
    Public Property Value As T

    Public Sub New() 
    End Sub

    Public Sub New(name As String, value As T) 
        Me.Name = name 
        Me.Value = value
    End Sub

    Public Overrides Function ToString() As String {
        Return Name
    End Function
End Class

现在，当用户在ComboBox 2中进行选择时，他们可以根据“友好”文本做出选择，但您仍然可以访问所需的IP值。

最后，最好将所有数据访问权限移到与UI分开的位置，如下所示：

Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged

    Dim Query As String = "select * from test.boxinformation where Box_SN= @BoxSN ;"

    Using MySqlConn As New MySqlConnection("server=localhost;userid=NOTROOT;password=root;database=test"), _
          COMMAND As New MySqlCommand(Query, MySqlConn)

        COMMAND.Parameters.Add("@BoxSN", MySqlDbType.VarChar, 15).Value = ComboBox1.Text
        MySqlConn.Open()

        Using READER As MySqlDataReader = COMMAND.ExecuteReader()

            While READER.Read
                ComboBox2.Items.Add(New ComboItem(Of String)("Component A", READER.GetString("CP_IP")))
                ComboBox2.Items.Add(New ComboItem(Of String)("Component B", READER.GetString("PC_IP")))
                'Guessing at the names here, since they aren't in the question
                ComboBox2.Items.Add(New ComboItem(Of String)("Machine 1", READER.GetString("M1_IP")))
                ComboBox2.Items.Add(New ComboItem(Of String)("Machine 2", READER.GetString("M2_IP")))
            End While
            READER.Close()
        End Using
    End Using
End Sub

然后用你原来的方法调用它：

Public Module Data
    Private Const ConnectinString As String = "server=localhost;userid=NOTROOT;password=root;database=test"

    Public Function GetComponentIPs(BoxSN As String) As String()
        Dim Query As String = "select * from test.boxinformation where Box_SN= @BoxSN ;"

        Using MySqlConn As New MySqlConnection(ConnectionString), _
              COMMAND As New MySqlCommand(Query, MySqlConn)

            COMMAND.Parameters.Add("@BoxSN", MySqlDbType.VarChar, 15).Value = BoxSN
            MySqlConn.Open()

            Dim result(3) As String
            Using READER As MySqlDataReader = COMMAND.ExecuteReader()
                While READER.Read
                    'You could also do this with Tuples, or make another custom object (class) to hold this data to keep things strongly-typed

                    result(0) = READER.GetString("CP_IP")
                    result(1) = READER.GetString("PC_IP")
                    result(2) = READER.GetString("M1_IP")
                    result(3) = READER.GetString("M2_IP")
                    Return result
                End While
           End Using
        End Using
        Return result
    End Function
End Module

将文本分配给Reader.GetString（）值？

1 个答案: