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Validation problems when users blank out a textbox bound to a number field in vb.net windows app.

Posted on 2008-09-30
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Last Modified: 2013-11-26
In my VS 2008 vb.net project I have some textboxes bound to number fields in the DB. when the user enters a number, then blanks out the number and moves off the textbox and tries to save the record it fails because it trys to save an empty string in the record.
How can I best handle this?

thanks,
bmutch
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Question by:PACCAST-DEV
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6 Comments
 
LVL 53

Accepted Solution

by:
Dhaest earned 500 total points
ID: 22612002
What you need is to hook the Parse event and in the event handler check the
argument value. If it is a string and empty, set the value to System.DBNull.Value.

Binding aBinding = new Binding("Text", your_datasource,"your field name");
aBinding .Parse +=new ConvertEventHandler(Parse_Handler);


Source: http://www.sitepoint.com/forums/showthread.php?t=289691
Private Sub Parse_Handler(sender As Object, e As ConvertEventArgs) 
    If e.Value.[GetType]() = Type.[GetType]("System.String") Then 
        Dim s As String = DirectCast(e.Value, String) 
        If s.Trim().Length <= 0 Then 
            e.Value = System.DBNull.Value 
        End If 
    End If 
End Sub 

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LVL 100

Expert Comment

by:mlmcc
ID: 22614594
That is one method if you want NULLs in the field.

Generally I handle this through the LostFocus event.  I check if the value is valid and if not don't let them leave the textbox until they put a valid value in it.

mlmcc
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Author Comment

by:PACCAST-DEV
ID: 22615062
Yes, I do allow nulls in these number fields.
Dhaest: - I have to declare this binding variable for every (about 10) field I want to take care of in this manner?
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Author Comment

by:PACCAST-DEV
ID: 22615148
where does this line go:
aBinding .Parse +=new ConvertEventHandler(Parse_Handler);
 and this line gives error:
If e.Value.[GetType]() = Type.[GetType]("System.String") Then
error : operator = is not defined for types system.type...
0
 

Author Comment

by:PACCAST-DEV
ID: 22616983
looks like I got it working, lot of hassle to just take care of the empty textbox...
0
 

Author Comment

by:PACCAST-DEV
ID: 22638715
I used a variation of the "Binding" method above. Am dissappointed that this is so hard to do in VS...
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