TextBox validation in Windows Forms

I have some code that is meant to check a TextBox for certain characters, alt开发者_StackOverflow中文版hough for some reason I am having problems with "KeyChar" and "Handled" part of the code:

private void textBox5_Validating(object sender, CancelEventArgs e)
{
    string allowedCharacterSet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890.\b\n";

    if (allowedCharacterSet.Contains(e.KeyChar.ToString()))
    {
        if (e.KeyChar.ToString() == "."
            && textBox5.Text.Contains("."))
        {
            e.Handled = true;
        }
    }
    else
    {
        e.Handled = true;
    }

}

.............

Error   2   'System.ComponentModel.CancelEventArgs' does not contain a definition for 'KeyChar' and no extension method 'KeyChar' accepting a first argument of type 'System.ComponentModel.CancelEventArgs' could be found (are you missing a using directive or an assembly reference?)   D:\test\Form1.cs    602 48  App

As the error says, there is no KeyChar property in CancelEventArgs.

Either you have to switch to KeyPress Event (which has KeyChar property in it's event args) of the textbox or consider the string as a whole (rather than one char at a time) in Validating Event

How about using regular expressions instead?

private void TextBox5_Validating(object sender, System.EventArgs e)
{
    String AllowedChars = @"^a-zA-Z0-9.$";
    if(Regex.IsMatch(TextBox5.Text, AllowedChars))
    {
         e.Handled = true;
    }
    else
    {
         e.Handled = false;
    }
}

Or something along these lines....

Try using KeyPressEventArgs e instead of CancelEventArgs e

http://msdn.microsoft.com/en-us/library/system.windows.forms.keypresseventargs.aspx

Try the KeyPress event instead. This lets you prevent users from typing in a letter that you don't want (by setting e.Handled = true). You'll still want to use Validating to make sure that they didn't paste some bad data from the clipboard.