How do you use a class file in ASP.NET Web Forms Application?

Before you do anything else you will need to add the System.Net.Mail namespace to your SendEmail class file.

This will leave you with-

using System.Net.Mail;

public class SendEmail
{
    public void SendMailMessage(string from, string to, string bcc, string cc, string subject, string body)
    {
        // Instantiate a new instance of MailMessage
        MailMessage mMailMessage = new MailMessage();

        // Set the sender address of the mail message
        mMailMessage.From = new MailAddress(from);
        // Set the recepient address of the mail message
        mMailMessage.To.Add(new MailAddress(to));

        // Check if the bcc value is null or an empty string
        if ((bcc != null) && (bcc != string.Empty))
        {
            // Set the Bcc address of the mail message
            mMailMessage.Bcc.Add(new MailAddress(bcc));
        }      // Check if the cc value is null or an empty value
        if ((cc != null) && (cc != string.Empty))
        {
            // Set the CC address of the mail message
            mMailMessage.CC.Add(new MailAddress(cc));
        }       // Set the subject of the mail message
        mMailMessage.Subject = subject;
        // Set the body of the mail message
        mMailMessage.Body = body;

        // Set the format of the mail message body as HTML
        mMailMessage.IsBodyHtml = true;
        // Set the priority of the mail message to normal
        mMailMessage.Priority = MailPriority.Normal;

        // Instantiate a new instance of SmtpClient
        SmtpClient mSmtpClient = new SmtpClient();
        // Send the mail message
        mSmtpClient.Send(mMailMessage);
    }
}

None of the other "usings" in there are required, these are added by default by Visual Studio but aren't actually used in the class.

Then you can simply use the following in your page-

protected void sendBtn_Click(object sender, EventArgs e)
{
    SendEmail send = new SendEmail();

    send.SendMailMessage("[email protected]", "[email protected]", null, null, "Test e-mail", "Test e-mail");
}

I suspect the fact your class wasn't compiling was what was tripping you up. The above code all built without problems in a sample project.

Although it is beyond the scope of the question I'd be tempted to make the helper classes static so you don't have to instantiate a new copy of SendEmail all the time.

See http://msdn.microsoft.com/en-us/library/dfb3cx8s.aspx and http://msdn.microsoft.com/en-us/library/sf0df423.aspx for more details on the using directive.

I'd like to recommend these:

1. Add the namespace to your class file. using System.Net.Mail;

2. Provide arguments when you call the function (SendMailMessage).

3. Make class SendMail as a static class, SendMailMessage as static function.

Put your class file in the same folder where your code that calls sendBtn_Click is located. If your code with the handler has a line somewhere at the top that says namespace SomeNamespace {, make sure that the class file you copied also has the same line. Your curly braces may vary.

Generally what I would do is create a separate "Library" project in your visual studio solution and reference that from your main website project.

Your new SendMail class will go in it.

Sometimes it seems like you'll just need a few helper classes but the amount tends to grow over time. Separating things out also helps with compile speed/organization as the project grows.

Change your class file to:

namespace MyCompany
{
     public class SendEmail
     {
          //Class properties and methods here.
     }
}

Then in your web form code behind, add:

using MyCompany;

Here is some more information about using namespaces which you might find helpful.