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首页 > 解决方案 > 为什么 cmbStream.ValueMember = "id" 为所有值显示零而 cmbStream.DisplayMember = "name" 显示正确的值

mysql - 为什么 cmbStream.ValueMember = "id" 为所有值显示零而 cmbStream.DisplayMember = "name" 显示正确的值

问题描述

我正在按照教程将数据从数据库插入到组合框中，但即使 DisplayMember 正确显示，分配的 ValueMember 似乎对于所有数据都是相同的。

这就是我将数据添加到 ComboBox 的方式

Private Sub cmbStream_VisibleChanged(sender As Object, e As EventArgs) Handles cmbStream.VisibleChanged
    If cmbStream.Visible = True Then
        cmbStream.DataSource = GetStreamItems()
        cmbStream.DisplayMember = "name"
        cmbStream.ValueMember = "id"
    End If
End Sub

得到这样的数据后

Function GetStreamItems() As List(Of StreamItem)
    Dim streamItems = New List(Of StreamItem)
    Dim reader As MySqlDataReader
    MysqlConn = New MySqlConnection
    MysqlConn.ConnectionString = "server='" & My.Settings.MServer & "';user='" & My.Settings.MDbUser & "';password='" & My.Settings.MDbPass & "';database='" & My.Settings.MDb & "'"
    Dim sql As String = "SELECT id, name FROM tbl_streams"
    Dim Command As MySqlCommand
    MysqlConn.Open()
    Command = New MySqlCommand(sql, MysqlConn)
    Command.CommandTimeout = 30
    reader = Command.ExecuteReader()
    If reader.HasRows = True Then
        While reader.Read()
            streamItems.Add(New StreamItem(reader("id"), reader("name")))
        End While
    End If
    Return streamItems
End Function

这是 StreamItem 类

Public Class StreamItem
    Public Sub New(ByVal id As Integer, ByVal name As String)
        mID = id
        mName = name
    End Sub

    Private mID As Integer
    Public Property id() As Integer
        Get
            Return id
        End Get
        Set(ByVal value As Integer)
            mID = value
        End Set
    End Property

    Private mName As String
    Public Property name() As String
        Get
            Return mName
        End Get
        Set(ByVal value As String)
            mName = value
        End Set
    End Property
End Class

我在代码中做错了什么以使所有数据的 ValueMember 为零？

标签： mysqlvb.net

解决方案

您没有使用正确的变量来获取。它应该是 mID，而不是 id。

Public Property id() As Integer
    Get
        Return mID
    End Get
    Set(ByVal value As Integer)
        mID = value
    End Set
End Property

在 VB.NET 中，函数/属性的名称也用作返回值的某种变量。这与执行 Return 123 相同

Function SomeFunc() As Integer
    SomeFunc = 123
End Function

或者在你的情况下

Public Property id() As Integer
    Get
        id = mID
    End Get
    Set(ByVal value As Integer)
        mID = value
    End Set
End Property

由于你没有设置id，所以默认值为0。反正不要用那个特性，很混乱。

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