Tag: Ajax

Ok so here’s what you’re trying to do:

You have a button and when it’s pressed you want to have it fill a drop down list without a postback. So your first thoughts are, “I like Mentos” followed by, “WebMethod” since you of course read this super awesome post. Now it might look like this:

        function GetUserList()
        {
            PageMethods.GetUserList(OnGetUserListComplete);
        }

        function OnGetUserListComplete(result)
        {
            var dropdownList = $get('dropdownListID');
            for (var i = 0; i < result.length; i++)
            {
                var item;
                item = document.createElement("option");
                item.text = result[i].UserName;
                item.value = result[i].UserID;
                dropdownList.options.add(item);
            }
        }

And GetUserList would be called on click. Fine and dandy, but this sort of bad since you’re hardcoding the id of the control. Meh. You look back at the method and see that there just isn’t a way to pass in a name, and if you didn’t you would be sooooo wrong it hurts. Shame on you. Good thing I’m here. The way you’re going to do this is to use an anonymous method. You see, as it is the PageMethod call needs a method to call post completion and that’s all it takes in. (Well not completely true, it can take in parameters for the server side method, but that’s not the point.) So you have to find a way for that PageMethod to call the method after completion AND make sure it has the list name with it.

        function GetUserList(dropdownList)
        {
            PageMethods.GetUserList(function(result) {
                 OnGetUserListComplete(result, dropdownList); });
        }

        function OnGetUserListComplete(result, dropdownList)
        {
            for (var i = 0; i < result.length; i++)
            {
                var item;
                item = document.createElement("option");
                item.text = result[i].UserName;
                item.value = result[i].UserID;
                dropdownList.options.add(item);
            }
        }

Ooo pretty tricky huh?

        PageMethods.GetUserList(function(result) {
                 OnGetUserListComplete(result, dropdownList); });

See what I did there, I created an anonymous method to be called on completion and in turn it calls the original (Though modified) OnGetUserListComplete method now. And you thought javascript sucked.

So I’ve been looking for something to match the simplicity of the old Ajax.dll WebMethods (The ability to asychronously call a method on a class from javascript) since the project was abandoned by the owner. A lot of what I saw before involved WebServices which wasn’t horrible, but I wanted Ajax.WebMethods. Come to find out, this simplicity exists in 3.5.

So let’s say I want to click on a div and have it’s innerHTML be filled with some string. Sounds like a completely viable situation for any money making business… Anyways, I could do some kind of post back and fill it, or I could use an update panel (Uhg) or I could use a Web Service or I could just bang my head on the desk and get the same level of satisfaction. But then came 3.5 and something wonderful. Take this page:

    public partial class Test : System.Web.UI.Page
    {
        [System.Web.Services.WebMethod]
        [System.Web.Script.Services.ScriptMethod]
        public static String GiveMeString()
        {
            return "hi";
        }
    }

See somethig weird? Yeah that’s the magic of the class file. All I need is:

• A Static Method
• The WebMethod Attribute
• The ScriptMethod attribute
• Optionally something to return, but for this example it’s not optional just like Burt Renold’s mustache

And now the page file is ready, but what about the markup? Well, that’s next, so glad you asked. First the javascript:

        function ShowString()
        {
            var test = $get('ShowThings');
            PageMethods.GiveMeString(OnGiveMeStringComplete);
        }

        function OnGiveMeStringComplete(result)
        {
            var test = $get('ShowThings');
            test.innerHTML = result;
        }

First method is the method to call. The PageMethods object will allow the use of the class method that was created. The parameter being sent in is actually the method needing to be called when the server side call is complete. With that in mind, guess what the second method is… No, not ice cream. It’s the method called when the server call is compete. As you can see, I am simply changing the innerHTML of a div.

    <form id="form1" runat="server">
        <asp:ScriptManager ID="smMain" runat="server" EnablePageMethods="true" />
        <div id="ShowThings" style="background-color:Yellow;height:20px;width:20px;"
          onclick="ShowString()"></div>
    </form>

And there you have the markup. ScriptManager is a must in this case, but that’s pretty standard when dealing with Ajax in asp.net. The only other thing of note is the method call on the div’s onClick. Beyond that, it’s ready to go. And if you were to make this example yourself and click on the div, you will get a ‘hi’ string in it on the first click. Amazing.