Thursday, August 19, 2010

Microsoft introduces LightSwitch: Game changer or gadget showoff?

On VSLive 2010 Microsoft announced Visual Studio LightSwitch. In this article I want to take a short look at what it is, based on the information provided by Microsoft so far. Then I’ll share some of my thoughts on this with you about how this might affect us as developers.

So what is this LightSwitch thingy about?

Well, basically it is a new edition of Visual Studio 2010 that enables people to quickly build data oriented applications (are there any other types?). ‘Oh,’ I hear you say, ‘another Oracle Forms clone. That’s not going to be any good.’ Well, first of all I’d say go and take a look at the VSLive 2010 Keynote. Also there is a great introduction video here. And for more of a deep dive you can check out this video.

‘Ok, so it’s just the next Microsoft Access?’, I hear you ask. Well, not quite either. The big difference with the previously mentioned platforms is the fact that you get an application with a multi-tier architecture and you get to choose what your client is and what your data source is. You can even have multiple data sources and link them together. And if you need to take your application to the next level, there are all kinds of extensibility points in both the underlying framework and the IDE itself.

On the UI end they have figured a way to do better as well. In the IDE you don’t have a WYSIWYG editor, but a sort of a tree view so you can better see and understand what you’re doing. The generated UI is also based on templates, so you can easily update the look and feel of your application at one point. And then when you do want a WYSIWYG editor you just start up your application, click a button and your on your way.

All in all it seems that Microsoft has succeeded in building a tool attempted and failed by a lot of companies.

The holy grail of database oriented systems?

For decades a lot of companies have attempted to build a system where you would simply define a data model, press a button and presto, there is your new software. Most companies failed and some partly succeeded, but no one was able to build a system that would actually work in a broad spectrum of cases and still provide enough customizability to implement the very specific features needed in very specific applications.

Most of the time failure occurred because the software would be to generic and the resulting applications would not meet enough of the users needs. And when teams would attempt to implement code to satisfy these needs, they would either become to specific or to expensive.

But is it really that simple? I don’t think so. Most database oriented systems I’ve worked on/with always have some form of extra processing, connect to external systems in special ways or need some very specific UI. In practice I think that most application that professional developers work on will not be built with LightSwitch all of a sudden. There may be some, but not many. There will be many reasons not to build an application in LightSwitch, but the main reason will be that developers feel they might not have enough control to actually build was is required. Another important reason is that you don’t get to choose what technology is used to build your application.

‘So it’s not the holy grail, then? It must fail miserably’ I hear you say. Well, no.

LightSwitch as a game changer

LightSwitch will be a game changer. We will see less complicated systems being build in LightSwitch all over the place. For Microsoft I guess it is all about getting the smaller companies to go with them, instead of going open source. And they do give them an important advantage in allowing them to cheaply and easily build their own software and still keep that software scalable. So in that respect it is a game changer.

Another effect will not be seen until we have moved on a couple of years. Right now we see a lot of applications build in Microsoft Access, which have reached their limits and need a ‘professional’ rebuild. Usually that means bringing in a team of developers to get the job done. Changes are these applications will not be rebuild in LightSwitch. However, what will happen with the LightSwitch applications in a couple of years, when they have reached their limits? Exactly, developers will need to be extending those systems. Mind you, I do think this will greatly reduce the number of rebuilds of applications, as I expect Microsoft to come up with a good upgrade strategy for future versions of LightSwitch, making sure they are always running on the latest and greatest technology.

And finally I think we will be seeing more and more ‘secondary’ applications. What I mean by that is applications which are used to fill in some gaps in our current processes. For example, if you are building a LOB application and you have some tables in your databases, that your company needs to maintain for your customers, why would you not build the UI for that in LightSwitch? Or if you need to collect metadata for generating code, why not do that in LightSwitch? And there will be many other uses like this for LightSwitch where it can add to existing systems as well.


As with a lot of the new technologies that we’ve seen in the past decade, LightSwitch does provide us with another useful tool in our toolbox. It again takes away some of the repeating work we as developers do, so we can focus on what makes our software unique. This again will be a game changer, just not as a lot of people expect.

So what are your thoughts on LightSwitch? Let us know by leaving a comment.

Friday, August 6, 2010

Adventures while building a Silverlight Enterprise application part #35

In this post we’ll look into something I ran into while doing rework on our framework. It involves the order in which code gets executed when using events and such.

The situation

We’re currently in the process of getting our first deliverable out the door on time. One of the things that needed to be addressed before we can actually start testing this code properly, is to get a backlog of issues out of the way. I decided to do that myself as it gives me a better feel for what are common problems and what is the quality of work we as a team put out. Also I realized that issues may had arisen because of wrinkles in the framework architecture, where we’ve had to take shortcuts to get to our first deliverable and I wanted to be able to address these as needed.

Some architecture insight

For you to make sense of what I did to solve one of the problems I encountered, it is important to have some understanding of how our application works (at least at the client side). We host several ‘applications’ insight our Silverlight client. In the end we will have probably about six of these applications. Each application follows the same design. On the left there is navigation, consisting of a ‘menu’ and some UI to select records. Depending on the type of record the user selects and whatever authorization the user has we load modules to work with the data.

To create new records, we use a concept we call a task. This is basically a wizard like UI, which runs as a popup on top of the other UI. It consists of some of the same modules as used when the user navigates to a record, only in a different visual state. This makes for some interesting scenario’s as it is likely that there are two instances of the same module using and updating resources that only have a single instance.

One of these scenario’s is updating the navigation after creating a record through a task. As the task does not have any knowledge on what the module does, it is the modules responsibility to update navigation after creating a new record. To do that, it updates something we named ViewState, which in turn updates both the navigation and the modules that are needed to present this new record to the user.

However, creating the record is usually done in the first module of the task, before other modules can save their data (because they might need to create a relationship with the new record). This means that whenever the modules get the signal to load new data, that most of them can’t because the data is not there yet. It has everything to do with the order in which things are executed, especially because we use events to directly update our modules.

A design oversight

The fix is actually simple once you realize we had a design oversight in our ViewState. Why should you update navigation and load data into modules, when you have a popup presented to the user and the user can’t interact with the newly loaded data? It doesn’t make any sense. So the fix was to get the ViewState to hold any updates to the rest of the application if a popup is being presented and trigger the events once the popup is closed.

The first step to do that was to create a generic way to trigger the events in the ViewState. This is what I came up with:

   1: private void InvokeEvent<T>(MulticastDelegate target, T args) where T:EventArgs

   2: {

   3:     if (target != null)

   4:     {

   5:         if (PopupBridge.Bridge.IsPopupOpen)

   6:         {

   7:             EventHandlerQueueItem<EventArgs> queueItem = new EventHandlerQueueItem<EventArgs>();

   8:             queueItem.EventHandler = target;

   9:             queueItem.EventHandlerArguments = args;

  10:             _eventQueue.Enqueue(queueItem);

  11:         }

  12:         else

  13:         {

  14:             target.DynamicInvoke(new object[] { this, args });

  15:         }

  16:     }

  17: }

The InvokeEvent<T> method takes a MulticastDelegate (which represents the actual event instance) and an args argument based on T where T should always be an EventArgs or derive from it. To make this as easy to use as possible I first check to see if there is actually a valid target (which is null if no handlers are available). Next I check to see if there is any popup open. In our case there is a PopupBridge that has that information for us. Now if there is no poup open I simply call DynamicInvoke on the target and pass in a reference to the ViewState and the args argument.

If there is a popup open, though, I create a EventHandlerQueueItem. This is how that struct looks:

   1: internal struct EventHandlerQueueItem<T> where T:EventArgs

   2: {

   3:     public MulticastDelegate EventHandler;

   4:     public T EventHandlerArguments;

   5: }

As you can see it is a simple struct that has both a MulticastDelegate and can contain arguments to pass off to any handlers. Once we had that, we could now declare a Queue<T> to hold these instances. As we can’t write something like Queue<EventHandlerQueueItem<T>> I decided to use covariance and go with Queue<EventHandlerQueueItem<EventArgs>>.

Now all that remains is to trigger the events once the popup is closed. In our case the PopupBridge knows about this and triggers an event for it. The handler looks like this:

   1: void Bridge_PopupClosing(object sender, PopupClosingEventArgs e)

   2: {

   3:     if (!PopupBridge.Bridge.IsPopupOpen)

   4:     {

   5:         while (_eventQueue.Count > 0)

   6:         {

   7:             EventHandlerQueueItem<EventArgs> item = _eventQueue.Dequeue();

   8:             if (item.EventHandler != null)

   9:             {

  10:                 item.EventHandler.DynamicInvoke(new object[] { this, item.EventHandlerArguments });

  11:             }

  12:         }

  13:     }

  14: }

As there can be multiple popups open I still need to check if there is a popup open at that point. If they are all closed, we can just keep calling Dequeue and invoke the handlers until the queue is empty.

Now that we have solved this design oversight, modules that need to load data that was created in a task, will always be able to get that data from the server and everything works as expected.

I hope you find these pieces of code useful. If you have any questions or comments, please leave them below.