The problem is simple: I have a form with textboxes, and in one of those textboxes, I want users to enter either a positive or negative 2-digit number. I'm looking for an easy way to enforce this restriction, i.e. without having to parse the number and check whether its absolute value is below 100.
If I set the textbox maxlength to 2, they cannot enter numbers below -9. If the maxlength is 3, they can enter numbers above 99.
A masked textbox has no solution, I cannot make the "-" literal optional, or at least not that I know of.
What would be the simplest solution to this restriction: "An empty textbox will accept 2 input characters if no "-" is typed, otherwise it accepts 3"? Handling the change event to see if a "-" was typed and resetting maxlength seems a bit overkill...
You actually want a NumericUpDownControl. Use that, and set its Minimum and Maximum properties. No validation code required at all, and easily solves your problem.
If you're stuck on using a TextBox then in short you're not going to get the desired functionality you want without actually checking the number. You could write a UserControl to do this and you could reuse it, but you still have to write some validation code.
Just validate the integer using ASP.NET/Javascript style validation. This example uses a label with a ForeColor of Red to display validation messages.
private void numberTextBox_TextChanged(object sender, EventArgs e) {
int number;
bool isValid = int.TryParse(numberTextBox.Text, out number);
if (!isValid) {
validationLabel.Text = "Must be a two-digit number.";
validationLabel.Visible = true;
return;
}
if (number < -99 || number > 99) {
validationLabel.Text = "Must be between -99 and 99";
validationLabel.Visible = true;
return;
}
if (isValid) {
validationLabel.Visible = false;
// Do something else with your number
// if you need to.
}
}
There's nothing wrong with having to write code to do validation. You probably won't achieve good results using existing designer properties otherwise.