Why I might not want to use Flex

While waiting for my eclipse to shut down, because the Flex Builder plugin again made it crash, I decided to write a little about my Flex experience.

I’m now on the finish straight of a small-to-medium project which uses Flex as a front-end.

On first sight Flex is smooth and pleasant to work with. You draw a bunch of beautiful components, write three lines of actionscript, and here’s is our nice “advanced hello”. But whenever one gets more into the details, the immaturity of Flex (and ActionScript) is too visible, alas.

First, to start with the more general stuff:

• exception handling. For a Java-guy like me, the exception handling ‘not perfect’. When an Error is caught, all you can know about it is .. the error code. Isn’t this too 1990? Stacktraces you can somehow acquire by calling “trace”, but it requires some configurations.
• event handling. At first, it does not seem troublesome when you see the event handling mechanism. object.addEventListener(stringConstantEventType, handlerMethod). Ok, I don’t really mind the String constant (though I should), but the handler method accepts only an Event as an argument. (And when you write your method to have the wrong argument class it starts to feel strange). This makes it impossible to pass other arguments to the ‘listener’. Yes, you can use fields of the declaring class, but what if two asynchronous notifications happen? Actually, a brief look at the Ovserver (listener) pattern shows the right way to do this. I don’t know why it is so strange.
• multithreading. Here I still don’t get things quite well – I read that Flex is single-threaded, and there is no way of manipulating threads. What a shame – especially if the flash player supports multithreading. In fact Flex maybe supports some kind of multithreading, with which it serves asynchronous requests, but are these mechanisms accessible for the developer? Actually, my recent experience hints towards the hypothesis that Flex has 2 threads – one for UI and one for the alleged asynchronous requests. So only one async request at a time. I might be wrong, of course.
• dynamically typed AS3. Completely no problem with this, but something bothered me. When I referenced an objecet by its interface, the compiler did not know it is an Object, and so I couldn’t call its Object mehtods (toString()). So I need to cast it to Object (or whatever I want). And where did the dynamic typing go..?
• event dispatching. This might well go to the section above, but here I don’t mean the machanisms, but some strange implementation details. I have exactly two examples – the Event.COMPLETE is dispatched by an Image before the Image object has marked itself as completed. And this caused problems. Also, the Click event is not dispatched if MouseDown is.
• now on to some very specific things. Starting with the file upload. Something very basic and regularly needed. Prior to Flex 3.2 (and I’m using 3.1), there is not getBytes, or similar methods for a file. So the only option to send the file is via a Http request (instead of some remoting that I would prefer). But ok – I created a servlet which would parse the request, check the size, type, dimensions of the image, and return whether it is allowed to be uploaded or not. But much to my surprise, as far as I understand (please, anyone correct me if I’m wrong), there was no way of getting feedback from the server. So I had to think of a way. I thought of a solution, which I’m ashamed of – I used the HttpStatusError, and I mapped an arbitrary Http status code to a certain error (type not supported, size too big, etc.)
• fonts cannot be loading dynamically – they must be precompiled. Which is my case made me write an java image creation servlet, but I suppose that in the common case it would be sufficient.
• hibernate support – I only took a glimpse of the examples of a hibernate support, saw some re-definitions of collection mappings (<one-to-many ..), and ran away screaming.

So, from these points I dare to conclude that Flex is still immature. Version 5 might be really good. But not now, and not until some serious considerations and rafactoring.

That’s why I’m likely to propose GWT as a RIA solution for forthcoming projects.