ASP.NET Web Forms

All server controls must appear within a <form> tag, and the <form> tag must contain the runat=“server” attribute. The runat=“server” attribute indicates that the form should be processed on the server. It also indicates that the enclosed controls can be accessed by server scripts:

<form runat="server">
 
...HTML + server controls
 
</form>
</asp>

Note: The form is always submitted to the page itself. If you specify an action attribute, it is ignored. If you omit the method attribute, it will be set to method=“post” by default. Also, if you do not specify the name and id attributes, they are automatically assigned by ASP.NET.

Note: An .aspx page can only contain ONE <form runat=“server”> control!

If you select view source in an .aspx page containing a form with no name, method, action, or id attribute specified, you will see that ASP.NET has added these attributes to the form. It looks something like this:

<form name="_ctl0" method="post" action="page.aspx" id="_ctl0">
 
...some code
 
</form>

A form is most often submitted by clicking on a button. The Button server control in ASP.NET has the following format:

<asp:Button id="id" text="label" OnClick="sub" runat="server" />

The id attribute defines a unique name for the button and the text attribute assigns a label to the button. The onClick event handler specifies a named subroutine to execute.