Question

在我的应用程序中，我有一个数据绑定ComboBox，如下所示：

Dim listaCategoria As List(Of Ccategoria) = CAD.ObterTodosC()              
cbxAlterarCg.DataSource = listaCategoria
cbxAlterarCg.DisplayMember = "nomeCategoria"
cbxAlterarCg.ValueMember = "idCategoria"

班级代码（CAD）：

Public Shared Function ObterTodosC() As List(Of Ccategoria)
    Dim lstTodos As List(Of Ccategoria) = New List(Of Ccategoria)
    Try
        Using con As SqlConnection = New SqlConnection()

            con.ConnectionString = myDAC._connectionString
            Using cmd As SqlCommand = con.CreateCommand()

                cmd.CommandText = "select * from Categoria"
                con.Open()
                Dim dr As SqlDataReader = cmd.ExecuteReader()
                While dr.Read()
                    Dim p As Ccategoria = New Ccategoria()
                    p.IdCategoria = dr.GetInt32(0)
                    p.NomeCategoria = dr.GetString(1)
                    lstTodos.Add(p)
                End While
            End Using
        End Using
    Catch ex As SqlException
        Throw ex
    Catch ex As Exception
        Throw ex
    End Try
    Return lstTodos
End Function

属性：

Public Class Ccategoria
    Private _idCategoria As Integer
    Private _nomeCategoria As String
    (...)

我的ComboBox显示“nomeCategoria”，其中“idCategoria”值为right。

现在我的问题，就像标题所说我可以创建一个默认的只读项目，所以说（“选择你的类别”）或类似的东西？

我已经看过其他一些教程，但是ComboBox都没有数据限制。

Answer 1

您可以做的是在Ccategoria()下lstTodos添加Dim lstTodos As List(Of Ccategoria) = New List(Of Ccategoria)，如下所示：

Public Shared Function ObterTodosC() As List(Of Ccategoria)
    Dim lstTodos As List(Of Ccategoria) = New List(Of Ccategoria)

    Dim p As Ccategoria = New Ccategoria()
    p.IdCategoria = 0
    p.NomeCategoria = "select your category"
    lstTodos.Add(p)

    Try
        Using con As SqlConnection = New SqlConnection()

            con.ConnectionString = myDAC._connectionString
            Using cmd As SqlCommand = con.CreateCommand()

                cmd.CommandText = "select * from Categoria"
                con.Open()
                Dim dr As SqlDataReader = cmd.ExecuteReader()
                While dr.Read()
                    Dim p As Ccategoria = New Ccategoria()
                    p.IdCategoria = dr.GetInt32(0)
                    p.NomeCategoria = dr.GetString(1)
                    lstTodos.Add(p)
                End While
            End Using
        End Using
    Catch ex As SqlException
        Throw ex
    Catch ex As Exception
        Throw ex
    End Try
    Return lstTodos
End Function

这样做只需添加DataSource即可。然后，您可以通过检查idCategoria是否为0来查看提供验证。如果是，您可能需要考虑向用户显示MessageBox，提示他们选择一个类别。

如何使用DataSource为ComboBox创建默认项

1 个答案: