Validating User Input

[highflight1985]

This may seem like a silly question, but how do I verify that the data a user enters is the right type of data. That is, I need a number to do math with, I can't allow the user to enter text. How do I check this at runtime?

[jmcilhinney]

This is a very oft-asked question, so a forum search would yield plenty of information.

The easiest way is to use a NumericUpDown control. If that's not suitable then you can use the TryParse of the appropriate numeric type, e.g.

Dim number As Integer
 
If Integer.TryParse(myTextBox.Text, number) Then
    'The "number" variable contains the numeric value.
Else
    'The TextBox does not contain a valid number.
End If

If the NUD is not suitable for whatever reason then the most professional way is to inherit the TextBox and prevent the user entering invalid characters at all. There are numerous examples of doing this by handling the KeyPress event already posted so I won't add to their number. Note though, that to do a full and proper job there is more to consider than just that.

Finally, the WFC link in my signature includes a NumberBox control that does what I just mentioned. It is the most complete implementation that I've seen that doesn't cost money.