.NET fulltext autocomplete in a combobox. Any performance-positive way of overriding listitems? - vb.net

Question

I'm struggling to meet a demand from my supervisors. I really hope that someone could give some advice.
Basically there are places in our project where there is a big selection of options. The most concrete example is choosing a city in the world. The items are hundreds of thousands.
Using standard winforms controls and properties, one can search through a list fast.
The problem is that we're using a concatenation of city&district name for all the items. Essentially PREFIX autotomplete works but does not work as needed. The task is to filter and show items by any given string in any part of the item. Essentially a FULL TEXT search in the combobox.
Does anyone have an idea about switching autocomplete sources in runtime relatively qiuckly and handling the suggest/suggestappend event?
Also the project is in VB.NET, though any form of .NET advice will be extremely helpful.
Thanks!
UPDATE: The latest attempt using competent_tech's suggestion with some minor modifications.
Imports System.Data
Public Class Form1
Private _ErrorText As String
Private _CommandExecuted As Boolean
Private m_fOkToUpdateAutoComplete As Boolean
Private m_sLastSearchedFor As String = ""
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Call Me.SetStatusText("Loading...")
Me._ErrorText = ""
Me.Cities.Clear()
Me.BackgroundWorker1.RunWorkerAsync()
End Sub
Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Try
Me._CommandExecuted = True
Me.Ara_airportsTableAdapter.Fill(Me.Cities.ara_airports)
Catch ex As Exception
_ErrorText = ex.Message
End Try
End Sub
Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
If Me._ErrorText = "" Then
Me.SetStatusText(Me.Cities.ara_airports.Count & " Records loaded")
Else
Me.SetStatusText(Me._ErrorText)
End If
Me.BindingSource.ResetBindings(False)
End Sub
Private Sub SetStatusText(ByVal sText As String)
Me.Text = sText
End Sub
Private Sub cboPort_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles cboPort.KeyDown
Try
If e.KeyCode = Keys.Up OrElse e.KeyCode = Keys.Down Then
m_fOkToUpdateAutoComplete = False
Else
m_fOkToUpdateAutoComplete = True
End If
Catch theException As Exception
' ...
End Try
End Sub
Private Sub cboPort_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboPort.KeyUp
Try
If m_fOkToUpdateAutoComplete Then
With cboPort
If .Text.Length >= 2 Then
Dim cSuggestions As IList
Dim sError As String = ""
m_sLastSearchedFor = .Text
cSuggestions = GetSuggestions(m_sLastSearchedFor)
.DataSource = Nothing
If cSuggestions IsNot Nothing Then
.BindingContext = New BindingContext
.DisplayMember = "CName"
.ValueMember = "id"
.DataSource = New BindingSource(cSuggestions, Nothing)
System.Threading.Thread.Sleep(10)
System.Windows.Forms.Application.DoEvents()
.DroppedDown = True
.Text = m_sLastSearchedFor
If .Text.Length > 0 Then .SelectionStart = .Text.Length
End If
End If
End With
End If
Catch theException As Exception
' ...
End Try
End Sub
Private Function GetSuggestions(ByVal searchFor As String) As IList
BindingSource.Filter = "CName LIKE '%" & searchFor & "%'"
Return BindingSource.List
End Function
End Class

Answer 1

The way we address this with very large sets of data (full set of drug information) is:
1) Handle the combo's TextChanged event
2) Within this event, get the list of suggestions that match the user's current input from the database. We leverage the power of database searching to find matches anywhere within the string.
3) When the suggestions are retrieved, bind them to the combobox
4) Wait for a little bit (500ms) to let the UI catch up (we use a combination of System.Threading.Thread.Sleep and System.Windows.Format.Application.DoEvents()).
A couple of notes on this approach:
1) Nothing is bound to the list when the form is first opened
2) We wait until the user has entered at least 4 characters before we start searching to reduce the hit on the DB and improve the user experience (you don't want to show all of the matches for A, for example).
Update with code to show full solution:
Here are some additional notes and code to show the actual process.
The ComboBox should be configured with all of the properties set to their default values with the exception of:
AutoCompleteMode = SuggestAppend
PreferredDropDownSize = 0, 0
Here is the code that we use for our specific situation (searching first four chars) with a placeholder for retrieving and assigning the data:
Private m_fOkToUpdateAutoComplete As Boolean
Private m_sLastSearchedFor As String = ""
Private Sub cboName_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles cboName.KeyDown
Try
' Catch up and down arrows, and don't change text box if these keys are pressed.
If e.KeyCode = Keys.Up OrElse e.KeyCode = Keys.Down Then
m_fOkToUpdateAutoComplete = False
Else
m_fOkToUpdateAutoComplete = True
End If
Catch theException As Exception
' Do something with the error
End Try
End Sub
Private Sub cboName_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboName.TextChanged
Try
If m_fOkToUpdateAutoComplete Then
With cboName
If .Text.Length >= 4 Then
' Only do a search when the first 4 characters have changed
If Not .Text.Substring(0, 4).Equals(m_sLastSearchedFor, StringComparison.InvariantCultureIgnoreCase) Then
Dim cSuggestions As IEnumerable
Dim sError As String = ""
' Record the last 4 characters we searched for
m_sLastSearchedFor = .Text.Substring(0, 4)
' And search for those
cSuggestions = GetSomeSuggestions(m_sLastSearchedFor) ' Your code here
.DataSource = Nothing
If cSuggestions IsNot Nothing Then
' Because this can use the same data source as the list, ensure that
' the bindingcontexts are different so that the lists are not tied to each other
.BindingContext = New BindingContext
.DataSource = cSuggestions
' Let the UI process the results
System.Threading.Thread.Sleep(10)
System.Windows.Forms.Application.DoEvents()
End If
End If
Else
If Not String.IsNullOrEmpty(m_sLastSearchedFor) Then
' Clear the last searched for text
m_sLastSearchedFor = ""
cboName.DataSource = Nothing
End If
End If
End With
End If
Catch theException As Exception
' Do something with the error
End Try
End Sub