Combo Box triggers another comboxbox display

[dr223]

Hi,

On my form I have 3 combo boxes,

CmbTruckTyp (has dropdownlist of Daf & Mercedes Benz)
cmbDafModels (A, B , C)
cmdMercBenzModels (D, E, F)


On Form Load (by default)

Select Truck Type = CmbTruckTyp (Daf is at the top) Select Model = cmbDafModels (set to visible at form load and cmdMercBenzModels set to false)

Now when a user from the dropdownlist on CmbTruckTyp select Mercedes Benz I want to hide the contents of cmbDafModels and display cmdMercBenzModels instead.

How can I achieve that? Is it the right approach to do it? I might have other 3 combo boxes to add...

Tried;

Private Sub CmbTruckTyp_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmbTruckTyp.SelectedIndexChanged

        If Me.CmbTruckTyp.Text = "Mercedes-Benz" Then
            cmdMercBenzModels.Visible = True
        Else
            cmbDafModels.Visible = False
        End If

        If Me.CmbTruckTyp.Text = "Daf" Then
            cmbDafModels.Visible = True
        Else
            cmdMercBenzModels.Visible = False
        End If

    End Sub

No errors, but doesnt work!!

When I Select Mercendez Benz from the dropdownlist, cmbDafModels disappears but cmdMercBenzModels is not visible.
When I click Daf again cmbDafModels doesnt reappear.

Many thanks

[dunfiddlin]

Private Sub CmbTruckTyp_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmbTruckTyp.SelectedIndexChanged
 
        If Me.CmbTruckTyp.Text = "Mercedes-Benz" Then '.Text is anything typed in so it's "" here and goes to Else
            cmdMercBenzModels.Visible = True
        Else
            cmbDafModels.Visible = False 'Daf box disappears
        End If
 
        If Me.CmbTruckTyp.Text = "Daf" Then '.Text is still "" so to Else
            cmbDafModels.Visible = True
        Else
            cmdMercBenzModels.Visible = False 'Merc box disappears
        End If
 
    End Sub

Private Sub CmbTruckTyp_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmbTruckTyp.SelectedIndexChanged
 
        If Me.CmbTruckTyp.SelectedItem = "Mercedes-Benz" Then
            cmdMercBenzModels.Visible = True
                   cmbDafModels.Visible = False
Else
            cmbDafModels.Visible = True
            cmdMercBenzModels.Visible = False
        End If
 
    End Sub

[dr223]

When I used the second code I received the error;


InvalidCastException was unhandled

Overload resolution failed because no Public '=' can be called with these arguments:
'Public Shared Operator =(a As String, b As String) As Boolean':

Thanks

[dunfiddlin]

It works without any problems on my machine, and that error doesn't relate to anything in the code as I have it. I'm assuming that cmdMercBenzModels is just a typo you made in naming the box and it's therefore valid. Otherwise I can't see anything that could be problematic.

[dr223]

Thanks - Changed cmdMercBenzModels to cmbMercBenzModels

Still I receive the same error at runtime

[dunfiddlin]

Please post your revised code.

[kevininstructor]

When I used the second code I received the error;


InvalidCastException was unhandled

Overload resolution failed because no Public '=' can be called with these arguments:
'Public Shared Operator =(a As String, b As String) As Boolean':

Thanks

This will work with Option Strict Off but not with Option Strict On

If Me.CmbTruckTyp.SelectedItem = "Mercedes-Benz" Then

This is the correct way for Option Strict On

If Me.CmbTruckTyp.SelectedItem.ToString = "Mercedes-Benz" Then

[dr223]

Ok - Tried

If Me.CmbTruckTyp.SelectedItem.ToString = "Mercedes-Benz" Then

When I select any other value not Mercedez-Benz - cmdMercBenzModels disappears and I receive an error as

NullReferenceException was unhandled
Object reference not set to an instance of an object.

If Me.CmbTruckTyp.SelectedItem.ToString = "Mercedes-Benz" Then
            cmbMercBenzModels.Visible = True
            cmbDafModels.Visible = False
        Else
            cmbDafModels.Visible = True
            cmbMercBenzModels.Visible = False

        End If

[dr223]

I also set Option Strict ON and tried both codes I still have the same error - any help please

[MotoX646]

Try this?

Private Sub CmbTruckTyp_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmbTruckTyp.SelectedIndexChanged
 
 Select Case Me.CmbTruckTyp.SelectedItem.ToString

    Case "Mercedes-Benz"
         cmdMercBenzModels.Visible = True
         cmbDafModels.Visible = False
    Case "Daf"
         cmdMercBenzModels.Visible = False
         cmbDafModels.Visible = True
    Case Else
         cmdMercBenzModels.Visible = False
         cmbDafModels.Visible = False

  End Select

End Sub

[dr223]

Ok Tried this ;

 Select Case Me.CmbTruckTyp.SelectedItem.ToString

    Case "Mercedes-Benz"
         cmdMercBenzModels.Visible = True
         cmbDafModels.Visible = False
    Case "Daf"
         cmdMercBenzModels.Visible = False
         cmbDafModels.Visible = True
    Case Else
         cmdMercBenzModels.Visible = False
         cmbDafModels.Visible = False

  End Select

At run time, I have the error -

NullReferenceException was unhandled by user code
Object Reference not set to an instance of an object

This line is higlighted in yellow;

Select Case Me.CmbTruckTyp.SelectedItem.ToString

ANy assistance please

[MotoX646]

NullReferenceException was unhandled by user code
Object Reference not set to an instance of an object

This line is higlighted in yellow;

Select Case Me.CmbTruckTyp.SelectedItem.ToString

You are getting that error because nothing is selected in the combobox. Your combobox's "selecteditem" is null. Your combobox must select something... By any chance do you have "CmbTruckTyp.SelectedItem = Nothing" anywhere in your code?

Try this:

If Not Me.CmbTruckTyp.SelectedItem = Nothing Then

 Select Case Me.CmbTruckTyp.SelectedItem.ToString
    Case "Mercedes-Benz"
         cmdMercBenzModels.Visible = True
         cmbDafModels.Visible = False
    Case "Daf"
         cmdMercBenzModels.Visible = False
         cmbDafModels.Visible = True
    Case Else
         cmdMercBenzModels.Visible = False
         cmbDafModels.Visible = False

  End Select

End If

[dr223]

Ok Added;

 If Not Me.CmbTruckTyp.SelectedItem = Nothing Then

At run time I receive the error;

InvalidCastException was unhandled
Operator '=' is not defined for type 'DatarowView' and 'Nothing'

[dunfiddlin]

Use this instead ..

If CmbTruckTyp.SelectedIndex > -1 Then

[dr223]

 If CmbTruckTyp.SelectedIndex > -1 Then

            Select Case Me.CmbTruckTyp.SelectedItem.ToString

                Case "MERCEDES-BENZ"
                    cmbMercBenzModels.Visible = True
                    cmbDafModels.Visible = False
                Case "DAF"
                    cmbMercBenzModels.Visible = False
                    cmbDafModels.Visible = True
                Case Else
                    cmbMercBenzModels.Visible = False
                    cmbDafModels.Visible = False

            End Select

At runtime, no errors, however, when I select DAF, cmbDafModels.Visible is not set True , same applies when I select MERCEDES-BENZ, cmbMercBenzModels.Visible is not set to True.

Why?


Any help -- thanks

[dunfiddlin]

Try ..

Select Case Me.CmbTruckTyp.SelectedText

[MotoX646]

Select Case Me.CmbTruckTyp.SelectedText

SelectedText is only for the editable portion of a combobox, not for the items in the list.

 If CmbTruckTyp.SelectedIndex > -1 Then

            Select Case Me.CmbTruckTyp.SelectedItem.ToString

                Case "MERCEDES-BENZ"
                    cmbMercBenzModels.Visible = True
                    cmbDafModels.Visible = False
                Case "DAF"
                    cmbMercBenzModels.Visible = False
                    cmbDafModels.Visible = True
                Case Else
                    cmbMercBenzModels.Visible = False
                    cmbDafModels.Visible = False

            End Select

At runtime, no errors, however, when I select DAF, cmbDafModels.Visible is not set True , same applies when I select MERCEDES-BENZ, cmbMercBenzModels.Visible is not set to True.

Why?

The text is CASE SENSITIVE. If your combobox has "Mercedes-Benz" then Case "MERCEDES-BENZ" will not work. They have to be the same...

[dunfiddlin]

SelectedText is only for the editable portion of a combobox, not for the items in the list.

It's been one of those days!