Question

How can only valid characters be allowed in a Windows file system in a TextBox that can only appear as uppercase in Windows Forms?

Is there an easy way for this?

1. About the set of characters allowed in a Windows file system (Char.IsLetterOrDigit is not enough)

2. How do I make the typed characters uppercase?

Answer 1

Create a Textbox key press handler and Use Path.GetInvalidPathChars(), Path.GetInvalidFileNameChars() to check for a valid char and return the uppercase version if the char is valid.

   textBox1.CharacterCasing = CharacterCasing.Upper; 

   ...

   private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (Path.GetInvalidFileNameChars().Contains(e.KeyChar) ||
            Path.GetInvalidPathChars().Contains(e.KeyChar))
        {
            e.Handled = true;
        }
    }

[Of course, it would be more reusable to create a method rather than placing this code directly in the handler.]

UPDATED to reflect comments.