Combo box input validation - Xtreme Visual Basic Talk

08-07-2007, 01:31 AM

FragMagnet FragMagnet is offline

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Combo box input validation

As with most of the people who decide to join this forum, I'm rather new to VB. So far, most of my problems have been answered by a simple search, but this time around I wasn't so lucky, even after several attempts.

I'm using Visual Basic for Visual Studio 2005 at the moment, and basically what I'm trying to do is prevent my users from manually typing in a choice in a combo box that isn't in the selection I've given them. It's an unbound source, so it should be simple enough... I'm just having a hard time finding the right events/methods to use to do this in a neater manner than having to brute force it over the whole list. It feels too messy.

Edit: So far I've tried using the ComboBox.Validated() event, but somehow this seems counterproductive to me - I want the event to trigger when the contents are not valid, not when they're valid.

Apologies in advance if I put this in the wrong forum or if I didn't give the right info somehow... hopefully my first shot at asking for help wasn't a bad one.

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Last edited by FragMagnet; 08-07-2007 at 01:36 AM. Reason: update in info

08-07-2007, 06:50 AM

LaVolpe

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Welcome to the forum

Comboboxes have a few style properties. One of them only allows a user to select an item from the list: DropDown List. Now that is VB6, I am guessing .Net is similar. In the future you may wish to post .Net questions into that forum vs this one.

Using that style prevents any need for a Validate event because one can only select an item from the list, unless you are using Validate for some other reason. And when that style is set, the selection occurs on the Click event where the selected item can be obtained via the ListIndex property.

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08-07-2007, 07:01 AM

FragMagnet FragMagnet is offline

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That helps a lot, thank you.

Though if I may toss out one last question, I'm now having trouble with preventing blank data entry in a NumericUpDown element. Is there some option I need to enable to disallow a null value entry?

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08-07-2007, 01:43 PM

LaVolpe

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I have no experience with that control (not in VB6). Again, you may want to post .Net related questions in the .Net forum. Here's Microsoft's info on that control should you want to review it.

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08-08-2007, 01:27 AM

FragMagnet FragMagnet is offline

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Bah. My apologies once again.

But in any case, thanks a lot for helping out even if I was in the wrong place.

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08-08-2007, 08:43 AM

AtmaWeapon

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Preventing the NumericUpDown control from displaying a blank value actually seems to be kind of tricky, but a little investigation showed it isn't as bad as it seems.

The biggest hurdle to accomplishing this goal is the Text property doesn't appear in the property grid or Intellisense. This would seem to suggest that you can't directly get or set the text, which is a problem. When the control's text is blank, the internal value does not change, so it seemed there was no way to detect if the user input a blank value.

Indeed, the documentation seems to agree:

Quote:

The Text has no affect on the appearance of the NumericUpDown control; therefore, it is hidden in the designer and from IntelliSense.

Sometimes, though, it is good to follow hunches that the documentation doesn't know what it's talking about. Digging into the control's implementation proved interesting. Several methods exist to parse and validate the input text, and they were directly using the Text property. It was only when I looked at the declaration for the property that I understood what was going on:

Code:

<Browsable(False), Bindable(False), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden), EditorBrowsable(EditorBrowsableState.Never)> _
Public Overrides Property [Text] As String

The property is not inaccessible, simply hidden. Intellisense will not display the property, but using it provides the expected behavior. (So much for "having no effect"!)

This leaves you with some choices, but I think using the Leave event is the best. If you want to force focus back into the control you can, but in that case I suggest the Validating event. Here's an example of how you could get rid of blank entries:

Code:

    Private Sub numericUpDown1_Leave(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles numericUpDown1.Leave
        If String.IsNullOrEmpty(numericUpDown1.Text) Then
            numericUpDown1.Text = numericUpDown1.Value.ToString()
        End If
    End Sub

When the user leaves the control, this replaces a blank value with the control's current value.

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08-09-2007, 01:50 AM

FragMagnet FragMagnet is offline

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That was immensely helpful. Thanks so much, you saved me from my self inflicted headaches of perfectionism.

Thanks so much. I needed to make a good impression on my boss after all.

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