vb.net change combobox options depending on select

Question

I am creating a program which someone can input a search into a textbox and then narrow down the results using a series of comboboxes (or just use the comboboxes to search through everything).

The program looks like this: form 1

I have made the options in the 2nd combobox change using the following code:

Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
    Dim type As String = ComboBox1.SelectedItem
    Dim make As String = ComboBox2.SelectedItem
    Dim model As String = ComboBox3.SelectedItem
    Dim version As String = TextBox2.Text
    Dim memory As String = TextBox3.Text
    Dim problem As String = TextBox4.Text
    Dim casenumber As Integer = Int(Rnd() * 9999) + 1000
    If type = "Phone" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E: \phone.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
    ElseIf type = "Tablet" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E:\tablet.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
    ElseIf type = "Desktop computer" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E:\pc.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
    ElseIf type = "Laptop" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E:\laptop.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
        'Else
        'Dim objwriter As System.IO.StreamWriter
        'objwriter = My.Computer.FileSystem.OpenTextFileWriter("E:\unknown.txt", True)
        'File.AppendText("type:" And ComboBox1.Text And "make" & ComboBox2.Text And "model: " & ComboBox3.Text And "version: " And TextBox2.Text & "memory" And TextBox3.Text)
    End If
End Sub

However,the code won't work to change what is in the 3rd box. I have repeated the following code for each option:

Private Sub ComboBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox3.SelectedIndexChanged
    Dim type As String = ComboBox1.SelectedItem
    Dim make As String = ComboBox2.SelectedItem
    Dim model As String = ComboBox3.SelectedItem
    Dim version As String = TextBox2.Text
    Dim memory As String = TextBox3.Text
    Dim problem As String = TextBox4.Text
    If type = "Phone" Then
        If make = "apple" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\apple.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "samsung" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\samsung.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "htc" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\htc.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "Nokia" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\Nokia.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "Blackberry" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\blackberry.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next

I have checked the obvious problems like putting the wrong text file names and capital letters etc, but can't get this to work whatever I do.

Does anyone know why the third combobox remains blank even when both conditions are met (both combobox1 and 2 have the right thing selected)? Any suggestion would be much appreciated.

Answer 1

Firstly I suspect that this code :-

Dim type As String = ComboBox1.SelectedItem.ToString
Dim make As String = ComboBox2.SelectedItem.ToString
Dim model As String = ComboBox3.SelectedItem.ToString
Dim version As String = TextBox2.Text
Dim memory As String = TextBox3.Text
Dim problem As String = TextBox4.Text

shouldn't be in each if your events. They should really be placed somewhere that executes after all the information has been chosen yes?

OK for a start paste this into a text file called "device type.txt"

Phone,E:\phone.txt
Tablet,E:\tablet.txt
Desktop Computer,E:\pc.txt
Laptop,E:\laptop.txt

Then edit your phones.txt file and the rest of the above files to match that format e.g this phone.txt file

Apple,E:\apple.txt
Samsung,E:\samsung.txt
Htc,E:\htc.txt
Nokia,E\nokia.txt
Blackberry,E:\blackberry.txt

and so on for each item that links to another file. For the last files in the tree - which I presume are the files containing a list of the models for each brand of phone, just leave them as a simple list. No commas or anything after each model.

Use this code to do the populating of each ComboBox

Private Sub PopulateComboBox(ByRef cboBox As ComboBox, ByVal itemSource As String)
    RemoveHandler ComboBox1.SelectedIndexChanged, AddressOf ComboBox1_SelectedIndexChanged
    RemoveHandler ComboBox2.SelectedIndexChanged, AddressOf ComboBox2_SelectedIndexChanged
    RemoveHandler ComboBox3.SelectedIndexChanged, AddressOf ComboBox3_SelectedIndexChanged
    Dim devices As New List(Of item)
    Dim csvFlag As Boolean = False
    cboBox.Items.Clear()
    Using MyReader As New Microsoft.VisualBasic.
        FileIO.TextFieldParser(itemSource)
        If MyReader.ReadLine.Contains(",") Then csvFlag = True
    End Using

    Using MyReader As New Microsoft.VisualBasic.
        FileIO.TextFieldParser(itemSource)
        If csvFlag Then
            MyReader.TextFieldType = FileIO.FieldType.Delimited
            MyReader.SetDelimiters(",")
        End If
        Dim currentRow As String() = {"", ""}
        While Not MyReader.EndOfData
            Try
                If csvFlag Then
                    currentRow = MyReader.ReadFields()
                    Dim tempItem As New item
                    tempItem.item = currentRow(0)
                    tempItem.fileName = currentRow(1)
                    devices.Add(tempItem)
                Else
                    currentRow(0) = MyReader.ReadLine
                    Dim tempItem As New item
                    tempItem.item = currentRow(0)
                    tempItem.fileName = ""
                    devices.Add(tempItem)
                End If

            Catch ex As Microsoft.VisualBasic.
              FileIO.MalformedLineException
                MsgBox("Line " & ex.Message & "is not valid and will be skipped.")
            End Try
        End While
    End Using
    If csvFlag Then
        cboBox.DataSource = devices
    cboBox.DisplayMember = "item"
        cboBox.ValueMember = "fileName"
    Else
        cboBox.DataSource = devices
        cboBox.DisplayMember = "item"
        cboBox.ValueMember = "item"
    End If
    AddHandler ComboBox1.SelectedIndexChanged, AddressOf ComboBox1_SelectedIndexChanged
    AddHandler ComboBox2.SelectedIndexChanged, AddressOf ComboBox2_SelectedIndexChanged
    AddHandler ComboBox3.SelectedIndexChanged, AddressOf ComboBox3_SelectedIndexChanged
End Sub

What it does is firstly check to see if the file being read is a comma-delimited file.

If it is delimited, it will read the file referred to in itemSource and expect a pair of values. The first value is what you see in the box(the DisplayMember), and the second value is what clicking on the box actually returns(the ValueMember)

If the file isn't comma-delimited, it will just read each line and add it to the combobox so that it acts normally (this will be important for the last files in the tree)

Next you need these methods for the ComboBoxes

Private Sub PopulateComboBox1()
    PopulateComboBox(ComboBox1, "E:\device type.txt")
End Sub

Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
    PopulateComboBox(ComboBox2, ComboBox1.SelectedValue.ToString)
End Sub

Private Sub ComboBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox2.SelectedIndexChanged
    PopulateComboBox(ComboBox3, ComboBox2.SelectedValue.ToString)
End Sub

Private Sub ComboBox3_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox3.SelectedIndexChanged
    PopulateComboBox(ComboBox3, ComboBox2.SelectedValue.ToString)
End Sub

Call the method to populate Combobox1 possibly in the form's load event.