Question

I have the following problem in ASP.NET: there is a form that contains a textbox and a button next to it that is supposed to be pressed by the user after filling the box (sample on http://www.burnthespam.info, click "Pick your one", or when using ReCaptcha in a popup). Often, instead, users press ENTER key to submit the form.

This doesn’t cause the click event on the button to be triggered and possibly cause an unexpected behaviour. In burnthespam, I "tried" to solve by checking if there is data inside the text box (but now if you do something different than pressing ENTER it’s like you pressed it) to workaround it.

Do you know if there is another way to handle the form submission with ENTER key, or a Javascript snippet that when you press ENTER presses the button I like?

EDIT

I want to handle the ENTER key event on the server-side, ie. I already have

protected void button_Click(object sender, EventArgs e)
    {
        Response.Redirect(...);
    }

I want that method to be called not only when I submit the form using the button (click or space with it highlighted) but also when a user presses ENTER when focusing the text-box

EDIT 2

Do you know if it’s possible to programmatically click a button in Javascript? Maybe it’s not possible to prevent phishing/spamming (see Facebook and "share to friends" for example) but I still would like to ask…

Answer 1

There some ways you can set a default button using the form object DefaultButton property or the DefaultButton property of a panel, but I have found them to be unreliable in the past in various browsers so usually I rely on javascript.

The only downside to this code is you have to turn off event validation with a page directive, but it should fire off click events, and trigger validators and all that.

Here is an example the code that we use. Normally I would put the register function in a utility class, but for this example it is in the page code.
Try this out.

<%@ Page Language="C#" EnableEventValidation="false" %>

    <script runat="server">

        protected void cmdSubmit1_Click(object sender, EventArgs e)
        {
            litValue.Text = "Value 1 - You entered: " + txtValue1.Text;
        }
        protected void cmdSubmit2_Click(object sender, EventArgs e)
        {
            litValue.Text = "Value 2 - You entered: " + txtValue2.Text;
        }

        /// <summary>
        /// This function registers what button is clicked based on whatever control currently has focus
        /// so for example if the user password field has focus then you can cause the enter button to click
        /// if the enter key is pressed This works with ie and firefox as far as I know
        /// </summary>
        /// <param name="ControlWithFocus"></param>
        /// <param name="ControlToClick"></param>
        private void RegisterDefaultButton(System.Web.UI.Control ControlWithFocus, System.Web.UI.Control ControlToClick)
        {

            PostBackOptions p = new PostBackOptions(ControlToClick);
            p.PerformValidation = true;
            if (ControlToClick is Button)
            {
                p.ValidationGroup = ((Button)ControlToClick).ValidationGroup;
            }
            else if (ControlToClick is ImageButton)
            {
                p.ValidationGroup = ((ImageButton)ControlToClick).ValidationGroup;
            }
            else if (ControlToClick is LinkButton)
            {
                p.ValidationGroup = ((LinkButton)ControlToClick).ValidationGroup;
            }

            p.RequiresJavaScriptProtocol = false;

            AttributeCollection a = null;
            if (ControlWithFocus is HtmlControl)
            {
                a = ((System.Web.UI.HtmlControls.HtmlControl)ControlWithFocus).Attributes;
            }
            else if (ControlWithFocus is WebControl)
            {
                a = ((System.Web.UI.WebControls.WebControl)ControlWithFocus).Attributes;
            }

            if (a != null)
            {
                a["onKeyDown"] = string.Format("if (event.keyCode == 13) {{{0}}}"
                      , ControlToClick.Page.ClientScript.GetPostBackEventReference(p));
            }
        }


        protected void Page_Load(object sender, EventArgs e)
        {
            RegisterDefaultButton(txtValue1, cmdSubmit1);
            RegisterDefaultButton(txtValue2, cmdSubmit2);

        }

    </script>

    <html xmlns="http://www.w3.org/1999/xhtml">
    <head runat="server">
    </head>
    <body>
        <form id="form1" runat="server">
            Enter Value 1: <asp:TextBox ID="txtValue1" runat="server"></asp:TextBox>
            <br />
            Enter Value 2: <asp:TextBox ID="txtValue2" runat="server"></asp:TextBox>
            <br />
            <asp:Literal ID="litValue" runat="server"></asp:Literal>
            <asp:LinkButton ID="cmdSubmit1" runat="server" Visible="false" OnClick="cmdSubmit1_Click">Hidden Button 1</asp:LinkButton>
            <input id="cmdSubmit2" runat="server" visible="false" type="button" value="Hidden Button 2" onserverclick="cmdSubmit2_Click" />
        </form>
    </body>