MaskedTextBox - TextChanged Event Throws Error

Posted on 2012-03-28
Last Modified: 2012-03-28
Using VB.Net 2010 (Pro)

I hav a form which contains several standard text boxes and a few MaskedTextBox controls I use for date input (ie set mask format to short date).

I want to know when the form becomes "dirty", so I've put code to check the values in the text boxes against the original data.  This has worked fine for standard text boxes, which I put code in the "TextChanged" event to test for "dirty".  For that standard textboxes, I've combined the "TextChanged" handler into one single routine.

However, when I try the same thing for a MaskedTextBox, when starting the application it immediately throws an error that reads:
Value cannot be null
All I have done to get this error is add the "TextChanged" event,  I have not yet even put code in the event.

I have tried both having a seperate handler, as well as combining it with the standard TextBox handlers.  Both fail with the same error.

What's going on and, more importantly, how go I get it to work?

Question by:Clif
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Expert Comment

ID: 37776776
I do not believe the .Net maskedtextbox supports null values. In other words, it has to have a default value to begin with and compare to when the value is changed.

LVL 10

Author Comment

ID: 37776831
That explains the problem but doesn't offer a solution.

Expert Comment

ID: 37776977
Give it a default value. Any date will do. It just won't validate against a Null value.  (i.e. does myDate = Null)

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Accepted Solution

Rose Babu earned 500 total points
ID: 37776978
instead of "TextChanged" event can you use "Leave" event of a "MaskedTextBox "? then test the application once.
LVL 10

Author Comment

ID: 37777129

I can't put a default date, if there is no date to put (ie, it's not a financed vehicle, so there is no Payoff date).  Putting an arbitrary date in would be confusng to the user.

This is the reason I went with the MaskedTextBox instead of the DateTimePicker.
LVL 10

Author Closing Comment

ID: 37777149
The Leave event seems to work as I need.

Thanks.  :)

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