C# Limit textbox to number or letter only

Question

I have asked the same question before, the thread becomes messy somewhat. Now I think it is better to reorganize my question.

First, I only want the input character to be: A-Z, a-z, 0-9. there are only 62 characters allowed.

For below code, it can compile, which is good, but that is not what I want. I have tried both IF statement, both of them accept dot key. I don't want dot key.

Now here are two new questions:

• How to exclude dot key?
• I would like to move the code to a bool statement public static bool isTextboxOnlyNumberOrLetter(), which will be called by many textbox from multiple forms. How to write the bool statement? How to call it?

Thanks.

        private void txtUserID_KeyPress(object sender, KeyPressEventArgs e)
        {
            char ch = e.KeyChar;

            if (!char.IsNumber(ch) && !char.IsLetter(ch) && ch !=8 && ch != 46)  //8 is Backspace key; 46 is Delete key. This statement accepts dot key. 
            //if (!char.IsLetterOrDigit(ch) && !char.IsLetter(ch) && ch != 8 && ch != 46)   //This statement accepts dot key. 
            {
                e.Handled = true;
                MessageBox.Show("Only accept digital character or letter.");
            }

        }

Answer 1

Hi VAer,

>How to exclude dot key?

You need to remove the && ch != 8 && ch != 46, the IsLetterOrDigit has indicates whether a character is categorized as a letter or a decimal digit.

>I would like to move the code to a bool statement public static bool isTextboxOnlyNumberOrLetter(), which will be called by many textbox from multiple forms. How to write the bool statement? How to call it?

1. create a class into your project, like this:
   
2. call it in the form you want:
   

Best Regards,
Dylan

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Answer 2

To answer you immediate question, 46 is '.'

Answer 3

What you can do is check the input after it is submitted to see weither it contains any invalid characters. That would possibly be simpler and easier to implement.