/*---------------------------------------------------------------------------------

                                          DATA VALIDATION PROJECT
                                                      R. Kessler
                                                Created 12/26/06
                                                    For C# 2005

 ---------------------------------------------------------------------------------
//See lesson 4 Data Validation Project

 bool isLegalChar = false;            //used to filter out keystrokes



private void txtCustomer_Validating(object sender, CancelEventArgs e)
        {
            //---this fires before validated event. Use it with the ErrorProvider control. CausesValidation property
            //      for a textbox must be set to true (default).
            //      If the textbox is empty, I cancel the transaction and tell C# what they typed is not valid and this
            //      prevents the Validated event from firing. If the validated event fires, C# will think the textbox has valid data.
            if (txtCustomer.Text.Trim().Length == 0)
            {
                errorProvider1.SetError(txtCustomer, "Please enter customer name.");
                e.Cancel = true;               //this will cancel the Validated event which tells C# the data IS valid
            }
            else
            {
                errorProvider1.SetError(txtCustomer, "");
            }
        }

        //_____________________________________________________________________________
        //Use both the Keypress & KeyDown events to trap your keys. Keydown fires first!!!

        private void txtCustomer_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (isLegalChar)
                e.Handled = false;
            else 
                e.Handled = true;
            
        }

        private void txtCustomer_KeyDown(object sender, KeyEventArgs e)
        {
            isLegalChar = false;
            if ((e.KeyCode >= Keys.A && e.KeyCode <= Keys.Z) | (e.KeyCode == Keys.Space | e.KeyCode == Keys.Back))
                isLegalChar = true;
            else
                isLegalChar = false;
        }

        //_____________________________________________________________________________