为什么在VB.NET中没有出现Binding Combobox usingdictionary with the MS ACCESS database with dapper

Question

我正在尝试使用 VB.NET 中的 dapper 将字典与 MS ACCESS 数据库绑定组合框。

所以我希望使用字典的绑定出现在组合框中，即表格的

Result

Dictionarytest

我的代码实现可能有问题吗？

请指导我

谢谢

Public Class Form4
    Private bindingSource1 As BindingSource = Nothing
    Private connectionString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\dapperdemo.accdb;Persist Security Info=False;"
    Private CBFullList As Dictionary(Of String, Integer)
  Private Sub BindcomboboxColorCode()
        Using conn = New OleDbConnection(connectionString)
            conn.Open()
            Dim sql = "SELECT * FROM Dictionarytest"
            Dim CBFullList = conn.Query(Of Dictionarytest)(sql).ToDictionary(Function(row) row.Result, Function(row) row.Key)
            conn.Close()
        End Using
        ComboBox1.DisplayMember = "Key"
        ComboBox1.ValueMember = "Result"
        ComboBox1.DropDownHeight = 80
        ComboBox1.DropDownStyle = ComboBoxStyle.DropDown
        ComboBox1.AutoCompleteMode = AutoCompleteMode.None
        ComboBox1.AutoCompleteSource = AutoCompleteSource.None
        ComboBox1.DataSource = New BindingSource(CBFullList.ToList(), Nothing)
    End Sub
Private Sub Form4_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        CBFullList = New Dictionary(Of String, Integer)()
        BindcomboboxColorCode()
    End Sub
End Class
Public Class Dictionarytest
    Public Property Key() As Integer
    Public Property Result() As String
End Class

ms access 中的结果数据库

回答来自@jmcilhinney的更新代码

Public Class Form4
    Private bindingSource1 As BindingSource = Nothing
    Private connectionString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\dapperdemo.accdb;Persist Security Info=False;"
    Private CBFullList As Dictionary(Of Integer, String)
 Private Sub BindcomboboxColorCode()
        Using conn = New OleDbConnection(connectionString)
            conn.Open()
            Dim sql = "SELECT * FROM Dictionarytest"
            Dim CBFullList = conn.Query(Of Dictionarytest)(sql).ToDictionary(Function(row) row.Key, Function(row) row.Result)
            conn.Close()
        End Using
With ComboBox1
            .DisplayMember = "Value"
            .ValueMember = "Key"
            .DataSource = CBFullList.ToArray()
        End With
    End Sub
 Private Sub Form4_Load(sender As Object, e As EventArgs) Handles MyBase.Load
 BindcomboboxColorCode()
    End Sub
End Class

Answer 1

这里有两件事需要解决。首先，您的代码无法运行的具体原因。其次，你应该做什么来让它发挥作用并且更好地发挥作用。

它不起作用的具体原因是您绑定了一个空的

Dictionary

而不是您从查询中填充的。您在这里声明一个字段：

Private CBFullList As Dictionary(Of String, Integer)

然后，您毫无意义地创建一个空的

Dictionary

并将其分配给此处的该字段：

CBFullList = New Dictionary(Of String, Integer)()

然后，您忽略该字段并将填充的

Dictionary

分配给立即超出此处范围的局部变量：

Dim CBFullList = conn.Query(Of Dictionarytest)(sql).ToDictionary(Function(row) row.Result, Function(row) row.Key)

然后绑定空的

Dictionary

，您甚至不应该在此处创建：

ComboBox1.DataSource = New BindingSource(CBFullList.ToList(), Nothing)

即使您通过将填充的

Dictionary

分配给字段而不是局部变量来解决此问题，您的代码仍然无法工作，因为您的绑定是错误的。

我会将查询结果的

Key

和

Result

属性映射到

Key

项的

Value

和

Dictionary

属性。除非表的

Key

列中可能有重复的值，但考虑到名称，这会很奇怪。

Private CBFullList As Dictionary(Of Integer, String)

CBFullList = conn.Query(Of Dictionarytest)(sql).ToDictionary(Function(row) row.Key, Function(row) row.Result)

然后我会在

Value

:

 中显示项目的 

ComboBox

With ComboBox1
    .DisplayMember = "Value"
    .ValueMember = "Key"
    .DataSource = CBFullList.ToArray()
End With

如果需要，您可以使用

BindingSource

，但是，如果使用它有意义，您应该将其添加到设计器中的表单中。