验证Textbox的字符长度

private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
       if(Char.IsDigit(e.KeyChar) || e.KeyChar.ToString() =="." || e.KeyChar == )
      {
           //Indicate the System.Windows.Forms.Control.KeyPress event is not handled
           e.Handled = false;
       }
       else
       {
            e.Handled = true;
       }
}