Tuesday, May 6, 2008

Some Ajax/WCF things I learned

I'm reworking a small ad-hoc web application I wrote because like all ad-hoc tools, it got a rather permanent status. It's like they say: "Nothing is as permanent as a temporal solution".
I wrote the first version using ASP.NET MVC. The only reason I did so was because I wanted to experiment with MVC and they told me to create the application in any way I saw fit. So it was a great way to experiment a little. Now the web application will be used on a more permanent basis and we will have to actively maintain it I decided to rewrite it. Also an additional requirement made the whole MVC thing a little harder then I ought to be. So I rewrote the web application, but this time I decided to use a WCF JSON webservice and go all-out Ajax. Still experimental, but less CTP-al.

So my first order of business was to write a WCF webservice that did the things I needed it to do. This was easy. No hurdles there.
Did you know you can put a [DataMember] attribute on a private member? It will even show up in the WCF service while still being private in your code. I used this because I had some data that needed to be exposed in the webservice as a string, but as a different data type internally. So I made a private property that made a string out of that data and put the [DataMember] attribute on it. And then I had a public property without the attribute for use inside the code. Very handy.

Next up after getting the WCF webservice done was consuming it through JavaScript. Nothing really difficult here either. Just Google for JavaScript and WCF and you'll find lots of examples. That's what I did. The only thing I did ran into was that at first I tried to have two separate web projects. One for the WCF webservice and one for the web application. For some reason I never got the JavaScript to work with the WCF webservice. I don't think it's impossible, but after fiddling with the WCF configuration for an hour I gave up and just made it into one project and it worked.

After I got the WCF/JavaScript communication to work I started to work on the JavaScript logic. And in doing so I learned some stuff about JavaScript.

JavaScript isn't really object oriented, but you can fake it.
You can create a new 'object' using the new keyword and a function declaration:

var myObject = new MyObject(){}

If you leave out the 'new' keyword the variable "myObject" would contain a reference to a function named "MyObject". A function that doesn't do anything. But add the 'new' keyword and now it's something like an object.
Unfortunately I have no idea how to proceed any further. It's possible to add properties and methods to the object. but I'm not 100% sure how.Also I had the site working in Firefox and Internet Explorer 8 beta, but when I tried it with Internet Explorer 7 it didn't work. It turns out that doing something like:

var element = document.getElementById("someId"); element.setAttribute("class", "cssClass"); element.setAttribute("onclick", "alert('Yay!');");

Works perfectly in Firefox and IE8, but not in IE7. The annoying part is that if you use the Developer Toolbar in IE7 and inspect the DOM properties of the element they look good. I created a similar element in straight HTML and compared it to the element I added and setup dynamically through JavaScript, but I didn't see any difference. Yet it didn't work.
Turns out you can't do this in IE7 and you need to use the proper properties of the element to set stuff up. So the above needs to be:

var element = document.getElementById("someId"); element.className = "cssClass"; element.onclick = function() { alert('Yay!'); };

Luckily this also works in Firefox and IE8.

More as I learn more...

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