Question

I currently have an WinForm consisting of Name, Address, Zip Code, State, and Age.

Once the user inputs the data, they click the “Exit” button which confirms no fields are blank, then saves the data to a file. I want to add a Zip Code validation that confirms the textbox (ZipField) contains only numbers.

    private void Btn_Click(object sender, EventArgs e)
    {

        if (String.IsNullOrEmpty(NField.Text) || String.IsNullOrEmpty(AField.Text) ||
            String.IsNullOrEmpty(ZField.Text) || String.IsNullOrEmpty(SField.Text) ||
            String.IsNullOrEmpty(AField.Text))
        {
            MessageBox.Show("Please complete", "Unable to save", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);

        return;
        }
        saveInfo();
        Form myForm = Start.getForm();
        myForm.Show();
        this.Close();
    }

Answer 1

See: http://www.codeproject.com/Articles/13338/Check-If-A-String-Value-Is-Numeric

public bool isNumeric(string val, System.Globalization.NumberStyles NumberStyle)
{
    Double result;
    return Double.TryParse(val,NumberStyle,
        System.Globalization.CultureInfo.CurrentCulture,out result);
}

Edit:

Usage

private void saveAndExitBtn_Click(object sender, EventArgs e)
    {
        if (!isNumeric(custZipField.Text, System.Globalization.NumberStyles.Integer))
        {
            MessageBox.Show("Please enter a valid post code", "Unable to save", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            return;
        }

        if (String.IsNullOrEmpty(custNameField.Text) || String.IsNullOrEmpty(custAddressField.Text) ||
            String.IsNullOrEmpty(custZipField.Text) || String.IsNullOrEmpty(custStateField.Text) ||
            String.IsNullOrEmpty(custAgeField.Text))
        {
            MessageBox.Show("Please complete the entire form", "Unable to save", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);

        return;
        }

        //save the data
        saveNewCustomerInfo();
        //next, retrieve the hidden form's memory address
        Form myParentForm = CustomerAppStart.getParentForm();
        //now that we have the address use it to display the parentForm
        myParentForm.Show();
        //Finally close this form
        this.Close();
    }//end saveAndExitBtn_Click method

    public bool isNumeric(string val, System.Globalization.NumberStyles NumberStyle)
    {
        Double result;
        return Double.TryParse(val, NumberStyle,
            System.Globalization.CultureInfo.CurrentCulture, out result);
    }