The ComboBox Control


I. Summary

The Items Collection of a ComboBox is the simplest way to populate a ComboBox with values. However, when building most software applications you will find that it is more logical to use a numeric value for each of the text values in the ComboBox. This is even more so true when building a database driven application that is based on a relational database.

II. Screenshots

The ComboBox Control The ComboBox Control

III. Sample Code

A. Data

  1. Items Collection
    Public Class frmCollectionComboBox
     Private Sub btnPopulateComboBox_Click(sender As Object, e As EventArgs) Handles btnPopulateComboBox.Click
      On Error Goto Errorhandler

        Me.ComboBox1.Items.Clear
        Me.ComboBox1.Items.Add("Chrysler")
        Me.ComboBox1.Items.Add("Dodge")
        Me.ComboBox1.Items.Add("Ford")
        Me.ComboBox1.Items.Add("GM")
        Me.ComboBox1.Items.Add("Honda")
        Me.ComboBox1.Items.Add("Hyundai")
        Me.ComboBox1.Items.Add("Kia")
        Me.ComboBox1.Items.Add("Nissan")
        Me.ComboBox1.Items.Add("Toyota")

      Exit Sub
      Errorhandler:
        Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
     End Sub

     Private Sub btnShowComboBoxText_Click(sender As Object, e As EventArgs) Handles btnShowComboBoxText.Click
      On Error Goto Errorhandler

        Msgbox(Me.ComboBox1.SelectedItem)

      Exit Sub
      Errorhandler:
        Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
     End Sub

     Private Sub btnSetBlankComboBox_Click(sender As Object, e As EventArgs) Handles btnSetBlankComboBox.Click
      On Error Goto Errorhandler

        Me.ComboBox1.SelectedIndex = -1

      Exit Sub
      Errorhandler:
        Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
     End Sub

     Private Sub btnIsComboBoxEmpty_Click(sender As Object, e As EventArgs) Handles btnIsComboBoxEmpty.Click
      On Error Goto Errorhandler

        If Me.ComboBox1.SelectedIndex = -1 Then
          Msgbox("ComboBox1 is empty.")
        Else
          Msgbox("ComboBox1 is not empty.")
        End If

      Exit Sub
      Errorhandler:
        Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
     End Sub

     Private Sub btnIsComboBoxHyundai_Click(sender As Object, e As EventArgs) Handles btnIsComboBoxHyundai.Click
      On Error Goto Errorhandler

        If Me.ComboBox1.SelectedText = "Hyundai" Then
          Msgbox("The selected ComboBox text is Hyundai.")
        Else
          Msgbox("The selected ComboBox text is not Hyundai.")
        End If

      Exit Sub
      Errorhandler:
        Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
     End Sub
    End Class
  2. Class Driven

    The Data Source Property of the ComboBox along with the DisplayMember and ValueMember Properties are used to populate a ComboBox with an ID and Text Value Pair.

    1. Write a Class that has a Property for the ID and a Property for the Text Value.
    2. Write a routine to initialize the Property Values of the Class.
    3. Create an instance of the Class for each Value in the ComboBox.
    4. Add each instance of the Class to a List that is of the Type of the Class.
    5. Bind the List to the Data Source Property of the Class.
    6. Set the DisplayMember Property of the ComboBox to the name of the Class Property that holds the Text Value.
    7. Set the ValueMember property of the ComboBox to the name of the Class Property that holds the ID Value

    There are many examples on the internet of how to bind a ComboBox to a DataSet. In my opinion, it is a better idea to use the Class driven approach described here instead of directly binding Controls on Forms to Recordsets or DataSets. 

    'Write a Class that has a Property for the ID and a Property for the Text Value.
    'Write a routine to initialize the Property Values of the Class.
    '--------------------------------------------------------------------------------------
    Public Class cCarCompany
        Private lCarCompanyID As Integer
        Private lCarCompanyName As String

        Public Property pCarCompanyID() As Integer

          Get
           pCarCompanyID = lCarCompanyID
          End Get

          Set(ByVal iCarCompanyID As Integer)
           lCarCompanyID = iCarCompanyID
          End Set

        End Property

        Public Property pCarCompanyName() As String

          Get
           pCarCompanyName = lCarCompanyName
          End Get

          Set(ByVal sCarCompanyName As String)
           lCarCompanyName = sCarCompanyName
          End Set

        End Property

        Public Function mInitializeCarCompanyClass( _
            ByRef iCarCompanyID As Integer, _
            ByRef sCarCompanyName As String) As Integer
          On Error Goto Errorhandler

           lCarCompanyID = iCarCompanyID
           lCarCompanyName = sCarCompanyName

          Exit Function
          Errorhandler:
          Msgbox (Err.Number & "-" & Err.Source & ": " & Err.Description)
        End Function

    End Class
     
    'Create an instance of the Class for each Value in the ComboBox.
    'Add each instance of the Class to a List that is of the Type of the Class.
    'Bind the List to the Data Source Property of the Class.
    'Set the DisplayMember Property of the ComboBox to the name of the Class Property that holds the Text Value.
    'Set the ValueMember property of the ComboBox to the name of the Class Property that holds the ID Value.
    '--------------------------------------------------------------------------------------
    Public Class frmClassComboBox
      Private Sub btnPopulateComboBox_Click(sender As Object, e As EventArgs) Handles btnPopulateComboBox.Click
        On Error Goto Errorhandler

          'Initialize Variables
          '-------------------------------------------
          Dim oCarCompanyList As List(Of cCarCompany)
          Dim oCarCompany(8) As cCarCompany
          oCarCompanyList = New List(Of cCarCompany)

          'Populate Objects
          '-------------------------------------------
          oCarCompany(0) = New cCarCompany
          oCarCompany(0).mInitializeCarCompanyClass(0, "Chrysler")
          oCarCompanyList.Add(oCarCompany(0))

          oCarCompany(1) = New cCarCompany
          oCarCompany(1).mInitializeCarCompanyClass(1, "Dodge")
          oCarCompanyList.Add(oCarCompany(1))

          oCarCompany(2) = New cCarCompany
          oCarCompany(2).mInitializeCarCompanyClass(2, "Ford")
          oCarCompanyList.Add(oCarCompany(2))

          oCarCompany(3) = New cCarCompany
          oCarCompany(3).mInitializeCarCompanyClass(3, "GM")
          oCarCompanyList.Add(oCarCompany(3))

          oCarCompany(4) = New cCarCompany
          oCarCompany(4).mInitializeCarCompanyClass(4, "Honda")
          oCarCompanyList.Add(oCarCompany(4))

          oCarCompany(5) = New cCarCompany
          oCarCompany(5).mInitializeCarCompanyClass(5, "Hyundai")
          oCarCompanyList.Add(oCarCompany(5))

          oCarCompany(6) = New cCarCompany
          oCarCompany(6).mInitializeCarCompanyClass(6, "Kia")
          oCarCompanyList.Add(oCarCompany(6))

          oCarCompany(7) = New cCarCompany
          oCarCompany(7).mInitializeCarCompanyClass(7, "Nissan")
          oCarCompanyList.Add(oCarCompany(7))

          oCarCompany(8) = New cCarCompany
          oCarCompany(8).mInitializeCarCompanyClass(8, "Toyota")
          oCarCompanyList.Add(oCarCompany(8))

          'Populate The ComboBox
          '-------------------------------------------
          Me.ComboBox1.Items.Clear
          Me.ComboBox1.DataSource = oCarCompanyList
          Me.ComboBox1.DisplayMember = "pCarCompanyName"
          Me.ComboBox1.ValueMember = "pCarCompanyID"
          Me.ComboBox1.SelectedIndex = -1

          'Clean Up Variables
          '-------------------------------------------
          oCarCompanyList = Nothing
          oCarCompany = Nothing

        Exit Sub
        Errorhandler:
          Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
      End Sub

    'Typical ComboBox tasks.
    '--------------------------------------------------------------------------------------
     Private Sub btnShowComboBoxText_Click(sender As Object, e As EventArgs) Handles btnShowComboBoxText.Click
      On Error Goto Errorhandler

          Msgbox("ComboBox SelectedValue: " & Me.ComboBox1.SelectedValue)
          Msgbox("ComboBox Text: " & Me.ComboBox1.Text)

        Exit Sub
        Errorhandler:
          Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description
      End Sub

     Private Sub btnSetBlankComboBox_Click(sender As Object, e As EventArgs) Handles btnSetBlankComboBox.Click
        On Error Goto Errorhandler

          Me.ComboBox1.SelectedIndex = -1

        Exit Sub
        Errorhandler:
          Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
     End Sub

     Private Sub btnIsComboBoxEmpty_Click(sender As Object, e As EventArgs) Handles btnIsComboBoxEmpty.Click
        On Error Goto Errorhandler

          If Me.ComboBox1.SelectedIndex = -1 Then
             Msgbox("ComboBox1 is empty.")
          Else
             Msgbox("ComboBox1 is not empty.")
          End If

        Exit Sub
        Errorhandler:
          Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
     End Sub

     Private Sub btnIsComboBoxHyundai_Click(sender As Object, e As EventArgs) Handles btnIsComboBoxHyundai.Click
      On Error Goto Errorhandler

          If Me.ComboBox1.Text = "Hyundai" Then
             Msgbox("The selected ComboBox text is Hyundai.")
          Else
             Msgbox("The selected ComboBox text is not Hyundai.")
          End If

        Exit Sub
        Errorhandler:
             Msgbox(Err.Number & "-" & Err.Source & ": " & Err.Description)
      End Sub

    End Class

B. AutoComplete

  1. AutoCompleteMode - Suggest
  2. AutoCompleteSource - ListItems

C. Events

  1. SelectionChangeCommitted - The SelectionChangeCommitted event is used to capture the event that is fired when a user manually chooses a new option from a ComboBox.
  2. SelectedIndexChanged - The SelectedIndexChanged event is used to capture the event that is fired when a user manually or programatically chooses a new option from a ComboBox.
  3. SelectedValueChanged - The SelectedValueChanged event is used to capture the event that is fired when a user manually or programatically chooses a new option from a ComboBox.