问题
Could someone help here?
I need to extract data from a Database into a combolistbox in VB.net. I have got the data, but now find that The first and the 'x' line need to be removed from the combolistbox (they are validation entries for another software) and shouldn't be selected for this application.
I tried to simply remove the offending entries from lists by using :- cbCubeARivet.Items.RemoveAt(index), but had an error letting me know I cannot use "Items" with a DataSource.
I decided to send the data to a listbox, and then try to transfer the entries to the combolistbox. This then lead me to getting multiple entries of System.Data.DataRowView in the combolist box. To demonstrate my problem I include an example code modified from MSDN.
Imports System
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Collections
Imports System.Data.SqlClient
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
' Populate the list box using an array as DataSource.
Dim SQLConnectionString As String = "Data Source=HL605\RIVWARE;Database=RIVWARE;Integrated Security=true;"
Dim mySQLConnection As New SqlConnection(SQLConnectionString)
mySQLConnection.Open()
Dim SQLDataTable As New System.Data.DataTable
'Create new DataAdapter
'Use DataAdapter to fill DataTable
Dim mySQLDataAdapter = New SqlDataAdapter("SELECT * FROM [Rivware].[dbo].[RivetTypes]", mySQLConnection)
mySQLDataAdapter.Fill(SQLDataTable)
ListBox1.DataSource = SQLDataTable
ListBox1.DisplayMember = "RivetType"
'original code from MSDN
'Dim USStates As New ArrayList()
'USStates.Add(New USState("Alabama", "AL"))
'USStates.Add(New USState("Washington", "WA"))
'USStates.Add(New USState("West Virginia", "WV"))
'USStates.Add(New USState("Wisconsin", "WI"))
'USStates.Add(New USState("Wyoming", "WY"))
'ListBox1.DataSource = USStates
' Set the long name as the property to be displayed and the short
' name as the value to be returned when a row is selected. Here
' these are properties; if we were binding to a database table or
' query these could be column names.
' Bind the SelectedValueChanged event to our handler for it.
AddHandler ListBox1.SelectedValueChanged, AddressOf ListBox1_SelectedValueChanged
' Ensure the form opens with no rows selected.
ListBox1.ClearSelected()
End Sub 'NewNew
Private Sub ListBox1_SelectedValueChanged(ByVal sender As Object, ByVal e As EventArgs)
If ListBox1.SelectedIndex <> -1 Then
TextBox1.Text = ListBox1.SelectedValue.ToString()
' If we also wanted to get the displayed text we could use
' the SelectedItem item property:
' Dim s = CType(ListBox1.SelectedItem, USState).LongName
End If
End Sub
End Class 'ListBoxSample3
Public Class USState
Private myShortName As String
Private myLongName As String
Public Sub New(ByVal strLongName As String, ByVal strShortName As String)
Me.myShortName = strShortName
Me.myLongName = strLongName
End Sub 'NewNew
Public ReadOnly Property ShortName() As String
Get
Return myShortName
End Get
End Property
Public ReadOnly Property LongName() As String
Get
Return myLongName
End Get
End Property
End Class 'USState
回答1:
I may not get this correct so here goes, the following uses mocked up data to display a string in both a ListBox and ComboBox where a integer is available by casting the current item as a DataRowView, access Row then access the data via Row.Field(Of Integer)("ID").
In the code I use a copy of the underlying DataTable for the ComboBox as using the same data table for listbox and combobox will cause one to traverse when is generally unwanted. The cast aspect would be done in another event but wanted to stay simple. Again I may not be on track here, let me know and can adjust to better suit your question.
Code using Option Infer On for the Linq anonymous statement which could be strongly typed too.
Dim dt As New DataTable
dt.Columns.Add(New DataColumn With {.ColumnName = "ID", .DataType = GetType(Integer)})
dt.Columns.Add(New DataColumn With {.ColumnName = "Name", .DataType = GetType(String)})
Dim data =
(
From M In System.Globalization.CultureInfo.CurrentCulture.DateTimeFormat.MonthNames
Where Not String.IsNullOrEmpty(M)).ToList.Select(
Function(monthName, index) New With
{
.ID = index, .Name = monthName
}
).ToList
For Each item In data
dt.Rows.Add(New Object() {item.ID, item.Name})
Next
ListBox1.DataSource = dt
ListBox1.DisplayMember = "Name"
ComboBox1.DataSource = dt.Copy
ComboBox1.DisplayMember = "Name"
Dim theTable As DataTable = CType(ComboBox1.DataSource, DataTable)
Dim theRow As DataRow = theTable.AsEnumerable _
.Where(
Function(row) row.Field(Of String)("Name") = "September") _
.FirstOrDefault()
If theRow IsNot Nothing Then
theTable.Rows.Remove(theRow)
End If
回答2:
Thanks again @Karen Payne,
I used your code to lead me in the right direction.
I created a new application and added a textbox, and two Listboxes, then paste the code. To run you will need to point to your own Server, Database, and Table.
This is what I came up with. It is useful as this will give you the actual data in a useable form:-
Imports System
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Collections
Imports System.Data.SqlClient
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
' get the data
Dim SQLConnectionString As String = "Data Source=HL605\RIVWARE;Database=RIVWARE;Integrated Security=true;"
Dim mySQLConnection As New SqlConnection(SQLConnectionString)
' Populate the list box using an array as DataSource.
mySQLConnection.Open()
Dim SQLDataTable As New System.Data.DataTable
'Create new DataAdapter
Dim mySQLDataAdapter = New SqlDataAdapter("SELECT * FROM [Rivware].[dbo].[RivetTypes]", mySQLConnection)
mySQLDataAdapter.Fill(SQLDataTable)
ListBox1.DataSource = SQLDataTable
ListBox1.DisplayMember = "RivetType"
' remove validation data from list
Dim Count As Integer
Dim X As Integer
'get the column of data to search for
For Count = 0 To ListBox1.DataSource.Columns.Count - 1
X = InStr(ListBox1.DataSource.Columns.Item(Count).ToString, "Name")
If X <> 0 Then Exit For
Next
' now search for any invalid rows, in that column. those containing "---"
Dim TheTable As DataTable = CType(ListBox1.DataSource, DataTable)
Dim theRow As DataRow() = TheTable.Select()
Dim RowNumber As Integer
For RowNumber = 0 To UBound(theRow) - 1
If theRow(RowNumber).Item(Count).ToString <> "---" Then
' data is OK so transer it to the other listbox
ListBox2.Items.Add(theRow(RowNumber).Item(Count - 1).ToString)
End If
Next
ListBox2.ClearSelected()
End Sub 'NewNew
Private Sub ListBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox2.SelectedIndexChanged
TextBox1.Text = ListBox2.SelectedItem.ToString()
End Sub
End Class 'ListBoxSample3
来源：https://stackoverflow.com/questions/34638431/why-i-am-getting-system-data-datarowview-instead-of-real-values-from-my-listbox