Adventures through the Silverlight

imageOver the last few weeks I’ve been having a few adventures in the world of Silverlight. A bit like Alice I’ve been following white rabbits down holes and through looking glasses. What I’ve discovered is that having an IDE doesn’t always make things easier, especially when the error is occurring somewhere between the chair and the keyboard, a place which is notoriously hard to debug.

Brain don’t fail me now

One issue I have is with my brain. If you start thinking as if the development environment is going to help you, then when it doesn’t it can completely throw the processes you use to figure stuff out, if indeed you can figure it out. Strangely enough (well for me anyway) if I’m in an environment where there is little help, read ‘no intellisense’, then my brain rewires itself for self help. This can often be easier on the development as I tend to check the code more and be more robust my development methodologies (i.e. checking my environment is setup correctly for one thing). Usually I find the differences in coding for Silverlight or using Dojo to follow these patterns (I often still use VS for Dojo, but obviously get precious little help!).

With Silverlight my development is all done in Visual Studio 2008 (with some design done in Expression Blend of course). Now 2008 is quite helpful when checking the syntax of C# code, but it can come off the imagerails with the XAML syntax, so once your done in blend and are hacking around with the mark-up you can often come unstuck. Many the time I’ve spent at the top of the page.xaml tinkering with the namespaces, wondering why the code wont work when I’ve copied it straight from the ArcGIS Silverlight API samples (note: always check the breaking changes in any of the API release notes like here as the samples sometimes lag behind the releases and don’t always correspond).

Other times the IDE just goes a bit spooky on you, such as when I added a new class to the top of my page.cs file (don’t ask me why I wasn’t refactoring things into different places, I was prototyping it’s allowed). Now I figured that this wouldn’t have been a problem, I’ve often slung a class at the top of a file and had no problem (or none I can remember!), but whilst the compilation and run of the application had no problem, the actual linking up of the page.xaml and the page.cs seem to have been b0rked.

Every time I needed to add a new event handler, or to navigate to an existing handler from the XAML to the code I would get the following error:

To generate an event handler the class ‘page’ must be the first class in the file.

Now I didn’t believe what my eyes were reading at first, of course I was using Visual Studio so my brain had partially shut down, therefore using my outsourced brain (read Google) I spent a few minutes imagetrawling the interweb in the hope of finding a solution. I did find it buried deep down in the following thread, where it spelt out the reason for my ‘code fail’ to be the fact that my new class was first in the code behind file, move the class to the end and hey-presto everything was tickety-boo.

Now this serves to highlight both my initial problem of my brain expecting simple issues like this to be sorted out by the wonder that is Visual Studio 2008 and secondly highlighting the fact that whilst an order of magnitude better than Visual Studio 2005 for its integration with Silverlight, it wont be 2010 that Microsoft will have a true development environment for it. Note to self, better get installing the 2010 RC when it’s released next month to check life will be peachy.

A Dash or Two

Where Silverlight (or any RIA environment, Flash, HTML 5) really excels is in the delivery of dashboards that allow for the easy cognitive processing of information without the clutter of hardcore GIS tools that are often prevalent in some internet mapping applications.

Indeed in my opinion (not necessarily anyone else’s though) if your using Silverlight to just deliver Y.A.M.A. (Yet Another Mapping Application) then unless you really need it to be rotating on a flying cube surrounded by dancing leprechauns (however tempting it might be) then you probably need to be using a more standard HTML/JavaScript based client, such as Dojo which doesn’t have the plug-in overhead.image

The ability to present and link multiple maps together, all updating in real time, with graphs and reports can really help sell the benefit of GIS to upper management, who often don’t get excited about data formats, tile caching and the different API’s. Show them the ability to visualise all their assets and modify their assignment in real time allowing for visual modelling of costs, then you might be on to a winner, show them the common operating picture of an unfolding disaster then you almost certainly are, especially if it can save money in the long run. Sure it might use all of the cool technologies under the hood, but most people who make decisions don’t care, they want simple tools that can leverage powerful geoprocessing tasks without even noticing. With good design and the interactivity given by Silverlight (and other RIA’s) then the move of GIS from allowing people to make niche decisions to impacting throughout the business should become a whole lot easier to show and use.

imageLet me at it – hold the white rabbit

Hopefully you can see not only the wonderland that can be offered by Silverlight but also the frustration that can occur if you blindly follow white rabbits around whilst developing.  If you don’t have time to build your own Silverlight client from scratch, you can always get a head start from one of the example applications fro
m the community section of the Silverlight resource center here or some nice examples of dashboards and UI can be seen on the ESRI North East Africa site here.

Which date is it?


I have to admit it I have a problem with dates. I always seem to draw a blank when trying to remember them; I’ve outsourced much of my anniversary notification to outlook and my iPhone, or work with them in applications. It has been ironic this week as the last decade ends and the next decade begins that the first thing that stumps me is a little date problem.

A choice of dates

I’ve been doing some development using the Silverlight API and I came to the part of the project where I needed to filter data using a date range and display on the map and in graph (or chart) form. Now querying with dates with any system is always tricky, especially with dates. Getting the right format can be the difference between date success and date fail! The right positioning of brackets or hash (US pound) symbols has often been the bane of my life.

As this is the Silverlight API I’m backing onto the ESRI REST API for my heavy lifting.  So I need to know the right REST syntax in order to create a correct query for use both as the ‘where filter’ for the feature layer as well as the ‘where filter’ for the query task. Fortunately the REST API provides a nice query form with which you can enter these parameters to your heart’s content (sample server example link).

imageNow, at this point you might think my work here is done, that this form and the collective knowledge of the internet (by that I mean my Google search box, to which I have outsourced my ability to remember syntax), would be able to get me to my goal of a working filter and in some ways it did, but then I found that there was a choice.

Choices Choices

Looking at the help page for the REST API here we can see the query layer section which gives the imagepossible filters for the whereas ‘any legal SQL where clause operating on the fields in the layer is allowed’. Now in the project that I was working on the dates being queried were in two different layers, one which was being filtered and the one providing the data for plotting on the graph. Both the layers contained one or more fields of the type “esriFieldTypeDate”, so I thought the same query would work on both, wouldn’t it?

Well it turns out that the answer is no. I initially started with one layer and was provided with the date format of #2009/01/01 00:00:00# which worked fine for querying a single field.

In usage this would give a query in the format of

"FIELDNAME > #2009/01/01 00:00:00#";

But when I applied this to another layer where I was filtering data by two date fields I got the strange error of:

“Unable to perform query. Please check your parameters.”

Hmm I thought, but it worked on the other layer (which is synonymous to the cry ‘but it worked on my machine’) so doing a bit of googling I managed to turn up a link on the forums where someone had had a similar problem and a suggestion to use the following syntax in the where clause:

"FIELDNAME > DATE ‘2009/01/01 00:00:00’";

This worked for both sets of queries. Whether it will work for all databases or data sets will require more imagetesting, but hopefully if your using dates in your application then this way of formatting a query for dates will hopefully work. If I come up with any more definitive answers for which format to use and where or a list of any other date formats that might not work with all datasets then i will endeavour to update this post!

Pointless Predictions

image As the first post of the year you might be expecting a string of pointless predictions about cloud computing, three screens and maybe a slate. Unfortunately I’ve yet to obtain the job title of ‘Futurologist’ so I’ll leave that to those sort of people who probably should really be out there doing a real job, like policeman, soldier or plumber, hmm I think I might need to shut up now and slink off with my Solution Architect business cards before someone outs me as a fraud.

Anyway enough of my blathering and hope you have had a happy new year up till now and your date searches will forever be successful.