Combo Box triggers another comboxbox display

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Aug 30th, 2012, 09:00 AM
dr223

Combo Box triggers another comboxbox display

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;

Code:

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

Re: Combo Box triggers another comboxbox display

vb.net Code:

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

vb.net Code:

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

Aug 31st, 2012, 04:30 AM
dr223

Re: Combo Box triggers another comboxbox display

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
Aug 31st, 2012, 07:19 AM
dunfiddlin

Re: Combo Box triggers another comboxbox display

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.
Aug 31st, 2012, 08:12 AM
dr223

Re: Combo Box triggers another comboxbox display

Thanks - Changed cmdMercBenzModels to cmbMercBenzModels

Still I receive the same error at runtime
Aug 31st, 2012, 08:30 AM
dunfiddlin

Re: Combo Box triggers another comboxbox display

Please post your revised code.
Aug 31st, 2012, 08:35 AM
kareninstructor

Re: Combo Box triggers another comboxbox display

Quote:

Originally Posted by 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

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

Code:

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

This is the correct way for Option Strict On

Code:

If Me.CmbTruckTyp.SelectedItem.ToString = "Mercedes-Benz" Then
Aug 31st, 2012, 08:59 AM
dr223

Re: Combo Box triggers another comboxbox display

Ok - Tried

Code:

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.

Code:

If Me.CmbTruckTyp.SelectedItem.ToString = "Mercedes-Benz" Then cmbMercBenzModels.Visible = True cmbDafModels.Visible = False Else cmbDafModels.Visible = True cmbMercBenzModels.Visible = False End If
Sep 2nd, 2012, 08:35 AM
dr223

Re: Combo Box triggers another comboxbox display

I also set Option Strict ON and tried both codes I still have the same error - any help please
Sep 2nd, 2012, 10:06 AM
MotoX646

Re: Combo Box triggers another comboxbox display

Try this?

Code:

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
Sep 3rd, 2012, 06:43 AM
dr223

Re: Combo Box triggers another comboxbox display

Ok Tried this ;

Code:

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;

Code:

Select Case Me.CmbTruckTyp.SelectedItem.ToString

ANy assistance please
Sep 3rd, 2012, 07:31 AM
MotoX646

Re: Combo Box triggers another comboxbox display

Quote:

Originally Posted by dr223

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

This line is higlighted in yellow;

Code:

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:

Code:

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
Sep 3rd, 2012, 08:14 AM
dr223

Re: Combo Box triggers another comboxbox display

Ok Added;

Code:

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'
Sep 3rd, 2012, 11:52 AM
dunfiddlin

Re: Combo Box triggers another comboxbox display

Use this instead ..

If CmbTruckTyp.SelectedIndex > -1 Then
Sep 4th, 2012, 04:20 AM
dr223

Re: Combo Box triggers another comboxbox display

Code:

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
Sep 4th, 2012, 12:18 PM
dunfiddlin

Re: Combo Box triggers another comboxbox display

Try ..

Select Case Me.CmbTruckTyp.SelectedText
Sep 4th, 2012, 12:34 PM
MotoX646

Re: Combo Box triggers another comboxbox display

Quote:

Originally Posted by dunfiddlin

Select Case Me.CmbTruckTyp.SelectedText

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

Quote:

Originally Posted by dr223

Code:

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...
Sep 4th, 2012, 01:40 PM
dunfiddlin

Re: Combo Box triggers another comboxbox display

Quote:

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

It's been one of those days! :eek: