RegularExpression

Question

Hello,

 

In text box i want to allow character,Number,Special Symbols like \ . ,-'

And also remove wrong character when i click on Messagebox.

 

Here is my code

private void txtPNo_TextChanged(object sender, TextChangedEventArgs e)

{

 

if (!System.Text.RegularExpressions.Regex.IsMatch(txtPNo.Text, "^[a-zA-Z0-9]*$"))
{
MessageBox.Show("This Textbox accepts only Alphabetes & Numeric Value");
txtPNo.Text.Remove(txtPNo.Text .Length -1);
} 

}

////error

 txtPNo.Text.Remove(txtPNo.Text .Length -1);//This line could not return anything

if first character is wrong then  length is 0 and it causes error