Problem with simple ComboBox
 

With this code:

Imports System.Text



Public Class Form1

    Public quoteStr As String = Global.Microsoft.VisualBasic.ChrW(34)

    Public illegalChar As Boolean = False

    Public asteriskReplacement As New StringBuilder(" ", 4)

    Public asteriskComboIndex As Integer = 0



    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

       Dim keyboardCharacters As String() = {" single space", "- hyphen", _

            " -  <single space>hyphen<single space>", "` open single quote",_

            "' close single quote", "_ underscore", "=", "~", "!", "@", "#", "$",_

            "%", "^", "&", "(", ")", "+", "[", "{", "}", ";", quoteStr, ",", ".", _

            "1", "2", "3", "4", "5", "6", "7", "8", "9", "0", "a", "b", "c", "d",_

            "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s",_

            "t", "u", "v", "w", "x", "y", "z", "A", "B", "C", "D", "E", "F", "G",_

            "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",_

            "U", "V", "W", "X", "Y", "Z"}        ComboBox1.Items.AddRange(keyboardCharacters)

        ComboBox1.SelectedIndex = asteriskComboIndex

    End Sub



    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)_

      Handles ComboBox1.SelectedIndexChanged

        Dim indexS As String = ComboBox1.SelectedIndex

        MsgBox("SelectedIndex _" + indexS + "_")

        Dim index As Integer = ComboBox1.SelectedIndex

        asteriskComboIndex = index

        WhichChar(ComboBox1, asteriskReplacement, index)

        MsgBox("SelectedIndexChanged SelectedText _" + ComboBox1.SelectedText + "_")

    End Sub



    Public Sub WhichChar(ByVal CBox As ComboBox, ByRef retVal As StringBuilder, ByVal index As Integer)

        MsgBox("WhichChar  CBox.SelectedText _" + CBox.SelectedText + "_")

        Dim selectedItem As New Object

        selectedItem = CBox.SelectedItem

        ClearStrBuilder(retVal)

        MsgBox("timing")

        Select Case index

            Case 0  'single space

                retVal.Append(" ")

            Case 1  'hyphen

                retVal.Append("-")

            Case 2  'single space>hyphen<single space>

                retVal.Append(" - ")

            Case 3  'open single quote

                retVal.Append("`")

            Case 4  ' close single quote

                retVal.Append("'")

            Case 5  'underscore

                retVal.Append("_")

            Case Else   'everything else

                retVal.Append(CBox.SelectedText)

        End Select

    End Sub



    Private Sub ClearStrBuilder(ByRef str As StringBuilder)

        Dim holdStr As String = str.ToString()

        str = str.Remove(0, holdStr.Length)

        str.Length = 0

    End Sub



    Private Sub Form1_FormClosed(ByVal sender As System.Object, ByVal e As System.Windows.Forms.FormClosedEventArgs)_

      Handles MyBase.FormClosed

        MsgBox("Form1_FormClosed asteriskReplacement _" + asteriskReplacement.ToString() + "_")

    End Sub



    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        MsgBox("Button1_Click asteriskReplacement _" + asteriskReplacement.ToString() + "_")

        MsgBox("Button1_Click  ComboBox1.SelectedText _" + ComboBox1.SelectedText + "_")

    End Sub



    Private Sub ComboBox1_Leave(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.Leave

        Dim indexS As String = ComboBox1.SelectedIndex

        MsgBox("ComboBox1 SelectedIndex _" + indexS + "_")

        Dim index As Integer = ComboBox1.SelectedIndex

        asteriskComboIndex = index

        WhichChar(ComboBox1, asteriskReplacement, index)

    End Sub

End Class

Create a default Windows Form Project with a default ComboBox and default Button in the default Form. Double-click the Form to open the code window, replace everything there with the above code. Run the code in the debugger – menu item Debug/Start Debugging . Close the spurious MsgBox.

Left click once in the ComboBox, press the <a> key (any valid file name character will do); left click the button. Note the two MsgBox messages report that no item was selected in the ComboBox (button click) and that nothing was entered into the asteriskReplacement StringBuilder (you may uncomment the “Timing” MsgBox in WhichChar() to verify that it is not entered). Note that in each message string I have wrapped the variable with a leading and trailing underscore so that null string variables look like __ <two underscores together> and a string containing a single space looks like _ _ <underscore><space><underscore>.

The problem is that when I enter a value via the keyboard (even adding a carriage return) the ComboBox does not enter the _SelectedIndexChanged() function. It does enter the _Leave() function (when I click the button), but note that by the time _Leave() is entered the .SelectedIndex value is no longer valid.

I have spent many hours trying to figure this out; it is obviously a very basic concept and everyone else uses this gadget with ease. I have no idea where I am going wrong. Any help would be greatly appreciated!

Re: Problem with simple ComboBox
 

A ComboBox, as it's name implies is a combination of a TextBox and a ListControl.
If you type an 'a' into the "TextBox" you will see that the ComboBox.Text property contains an 'a'. To put that 'a' into the dropdownlist you have to do a ComboBox1.Items.Add or .Insert

Re: Problem with simple ComboBox
 

Not quite what I am looking for. The "a" is already on the list of items, I do not want to add it. Think of the ComboBox in a web shopping cart--you are asked to fill in your credit card info...there are two comboBoxes to enter Expiration date--month and year. The month box has "1 (Jan)", "2 (Feb)", "3 (Mar)...etc. as possible items to select (I see this in lots of non-web Windows apps as well.)

What other tool would do this job?

Re: Problem with simple ComboBox
 

I think you need to check out the DropDownStyle property.
Set it to DropDownList.

Re: Problem with simple ComboBox
 

The SelectedIndexchanged() event only fires when you actually click an item to "change" the contents of the combobox.... perhaps "click" or "keypress" would be the right choice?