This post is a slight deviation from software to talk about the very interesting topic of Fractals…

Fractals mean different things to different people and are a very useful tool used in many ways, from tie-dye shirts to Star Wars animations to geographical measurements.

What are fractals?
Fractals are a mathematical construct, depicted as a geometric form that is composed of smaller pieces of itself. Thus it is possible to construct very complex shapes from very elementary ones using duplication.
A good article of fractals can be found at: http://mathworld.wolfram.com/Fractal.html

Benoit Mandelbrot invented the term  fractal, which he depicted using self-similarity and wrote a paper to compute the length of Britain’s coastline, which he depicted as a fractal.
The concept of self-similarity was not new and was around since the 1700s, but Mandelbrot defined it mathematically.
He defined a fractal dimension (figures composed of fractions) and faced opposition from classic mathematicians who were more about lines and curves and integral dimensions (whole parts made of ones and twos and so on).
http://math.bu.edu/DYSYS/chaos-game/node6.html#SECTION00060000000000000000 has a good explanation of this.

Mandelbrot defined a fractal to have the properties of self-similarity, fractal dimension and formation by iteration.What he essentially did was to describe nature in a mathematical form, which had never been done before when math was only applicable to human-made structures like buildings.

His paper was applied by many people to create complex shapes, e.g. artificial mountains were rendered by an animator at LucasFilms, who started with a simple triangle and replicated it multiple times. This started a whole world of realistic animations of natural forms like clouds, waves, etc.
Some practical applications are:
Cell-phone antennas where surface area is maximized by using a fractal shape.
Calculating the surface area of a forest to know how much CO2 it can absorb, which in a study was found to be fractal in nature (pun intended), and has the same form as that of a tree.
Similarly, clouds or oceans can be depicted as fractals and used for predictions.
A heartbeat waveform is apparently a fractal and not a clean sine or square wave. Thus irregular heartbeats can be detected if they don’t exhibit a fractal nature.

Here is a fractal I drew called the Pythagoras Tree, that starts with 1 triangle with 2 half-size triangles at 45 degrees, and that is repeated over.

Hope this opens up the wonderful world of fractals for you…

It’s been a while since I wrote about TFS although a post I made about it 5 years ago is still the most popular post on my blog (weird!), and I’d like to give a plug for a plug-in for TFS called Urban Turtle, that provides SCRUM tools for Agile development. 
The name seems like a play on Tortoise, which provides integration for SVN (a source-control system), and I have this vision of a turtle walking in a city with shades on and a boom-box on it’s shoulder.

The Urban Turtle website is at http://urbanturtle.com/, and it has all the info and videos for you to get started.
Brian Harry of the TFS team has a good post about it here: http://blogs.msdn.com/b/bharry/archive/2011/01/05/urban-turtle-for-scrum-and-tfs.aspx

I am still exploring it, but it seems to have all the features you’d require in a SCRUM tool.

The SCRUM features are available in the Project Portal (website on SharePoint), for easy web-access to all team-members (including clients)

Creating Sprints, for example.

image

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At work, we use TFS for source control and JIRA for SCRUM, but I don’t like the Printing possibilities of our JIRA setup, and assigning a Task to someone is not easy (because of a clunky interface with the name list).

Let’s see how things are in Urban Turtle land, and I’ll report back if I end up trying it.

We are currently developing an LOB application and one of the screens in Silverlight shows about 20,000 records. When the (Silverlight) client made the domain service call it got back no data. This was because the database calls took a long time and returned many records. This led to problems with RIA services on 2 levels viz. timeouts (the time the call takes to return) and the number of objects returned.
To resolve this, I did the following:

Setting the timeout

To work around the default timeout of 30 secs for RIA services, we need to over-ride the the timeout of the binding for the endpoint at run-time.
This is a simple concept but tricky to implement. The idea is to create a partial class that will complement the DomainContext class auto-generated for the Silverlight client.

To get a handle on this, open the auto-generated file by RIA services during compilation, named [your project].g.cs in a hidden Generate Code folder. To view this, click the Project for your Silverlight client as specified in the RIA services link.

image

Click on the “Show All files” button icon in VS2010 and you will see it.

This file will contain the proxy Domain Context class generated for calling your Domain Service, amongst many other namespaces and classes in that file. Ensure you have the right namespace for this class (it could be confusing) which is essentially the namespace of your Domain Service.

Create a partial class for this Context.
Make a new file and add code similar to the following to it
(replace myns and MyDomainContext with yours, and the required timeout value which I have as 5 minutes)

namespace myns
{
    public sealed partial class MyDomainContext
    {
        partial void OnCreated()
        {
            if (!DesignerProperties.IsInDesignTool)
            {
                ((WebDomainClient<MyDomainContext.IMyDomainServiceContract>)this.DomainClient)
                    .ChannelFactory.Endpoint.Binding.SendTimeout = new TimeSpan(0, 5, 0);
            }
        }
    }
}

 

Add a reference to the web client of Domain Services

image

If the class you added does not compile, check the namespace and the Interface name (from the hidden file for that domain context constructor) and the reference.

Changing the number of objects returned

RIA Services limits the number of objects that can be returned, and this limit can be over-ridden by modifying the service behavior (not the client). This is done by modifying the web.config file to first specify a behavior node

The existence of the behavior node is specified in the services section

<services>
  <service name="myNS.myDomainService" behaviorConfiguration="myDomainService" />
</services>
The actual behavior node is specified in the behaviors node in the system.serviceModel section. Minimize the number of objects returned to suit your needs
<behaviors>
<serviceBehaviors>    
<behavior name="myDomainService">
  <serviceMetadata httpGetEnabled="true" />
    <serviceDebug includeExceptionDetailInFaults="true" />
     <dataContractSerializer maxItemsInObjectGraph="2147483647"/>
</behavior>
</serviceBehaviors>
</behaviors>
The above changes should hopefully work for you as well.

While developing Win Phone apps, there are a few options for having a timer. Here are 2 possibilities which provide precision vs. blocking/overhead:

1. Dispatch timer
This is basically a timer that runs on the UI thread and so is precise but can block the UI for any refreshes and activity when it executes, so be careful how/when you use it.

It can be declared and created as:

System.Windows.Threading.DispatcherTimer _predictionTimer = new System.Windows.Threading.DispatcherTimer();

It is set up as: (Do this in the Page loaded event, for the Page)

_predictionTimer.Interval = new TimeSpan(0, 0, TIMER_INTERVAL_SECONDS);
_predictionTimer.Tick += new EventHandler(PredictionTimerEvent);
_predictionTimer.Start();

Note: If you type in the += after the second statement, hitting Tab twice will also generate a callback stub in code (like the one below) for you.

The method to call for the timer event is written as:

void PredictionTimerEvent(object sender, EventArgs e)
{
   …do something…}

2. IDisposible timer

This timer is not very precise, but runs on its own thread and not the UI thread  and so does not block the UI. It does need to switch contexts to do anything with the UI/display. So, you need to get a handle to the UI thread to do anything with the display. I use the MVVM Light Messenger and subscribe to a message that I then send in the timer so I don’t need to do any switching myself.

It is declared as:

        IDisposable _timer;

It is created as: (Do this in the Page loaded event)

if (_timer== null)

{

        IScheduler scheduler = Scheduler.Dispatcher;

    _timer = scheduler.Schedule

                              (new Action<Action<TimeSpan>>TimerInterrupt), 
                    TimeSpan.FromSeconds(TIMER_INTERVAL_SECONDS));

}

The timer event handler is written as:

        void TimerInterrupt(Action<TimeSpan> action)         {             …do something…             action(TimeSpan.FromSeconds(TIMER_INTERVAL_SECONDS));         }

To kill the timer (while navigating away, for e.g.)

_timer.Dispose();  //kill timer

Both of the above essentially do the same thing, but there are different reasons to use either.
Hope that helps.

It is a common scenario to navigate to another URI on a button click. If you have MVVM fully wired up, this command in your View will likely connect to a method in your ViewModel. But the View is the one that can navigate via the NavigationService.

So, this means the ViewModel will need to tell the View to do so. One way to do this is by using the Messaging framework in MVVM Light toolkit.

For e.g. Let’s say your About button needs to go to to the About Uri. The following are the various steps involved.

1. View – Register the Message (to receive) in the source View.
Let’s say we want to look for a Uri and a token of “Navigate”. When it is received, we want to invoke the Navigation. This can be elegantly done with a delegate as follows

Messenger.Default.Register<Uri>(this, "Navigate", 
        (uri) => NavigationService.Navigate(uri));

2. ViewModel – Send this Message from a ViewModel, and MVVM Light will deliver it to the View

private void About(object param)
{
    Uri uri = new Uri("/View/About.xaml", UriKind.Relative);
    Messenger.Default.Send<Uri>(uri, "Navigate"); 
}

This ensures there is no tight coupling between the ViewModel and the View, as the pattern requires.

You can use this pattern even between 2 Views if you need.

Here is a presentation about MVVM and implementing the design pattern with MVVM Light toolkit, that I made to the San Francisco Silverlight User group.

Feel free to use this as you may please.

As part of developing for WP7, I came across a few issues that I’d like to share with you, and maybe help you avoid some pitfalls I faced…

1. WebClient requests are cached by emulator
If you use the WebClient class to download information from the web, be aware that the web requests are cached by the emulator (and the actual phone?) and this can be quite confusing, especially for real-time data from the web. There is no straight-forward workaround, and the only way for me to get this working was to tag on a GUID in my query string. Something like:

downloadUrl = url + “&guid=” + Guid.NewGuid()

This, of course is a hack which might work with most websites because they only pick out params they care about and ignore the rest. Watch out for some strict sites that check for a fixed number of params and I have nothing around that at the moment.

2. Fiddler with WP7

As part of troubleshooting my first problem, I tried to use Fiddler which will not track WP7 web requests out of the box, but can be made to do so with the following steps:

  1. Start Fiddler (ensure you have the latest version).
  2. Click Tools > Fiddler Options.
  3. Open the Connections tab and tick the Allow remote computers to connect box. Click OK.
  4. In the QuickExec box (shown in red) under the session list, type prefs set fiddler.network.proxy.registrationhostname [HostName] where HostName is the name of your desktop computer.

image

   5. Close and restart Fiddler and the Windows Phone 7 Emulator.

Now you should  be able to track requests from the Emulator in Fiddler.

I referred to Eric’s blog post and the Phone 7 blog for this issue.

3. Application Icon and Splash Screen don’t show up in app
I replaced my ApplicationIcon.png and SplashScreenImage.jpg but was scratching my head when they did not show up at run-time. A little looking into showed that when I replaced the original files, I lost their Properties and these files need to marked as Content Resources, like this:

image

4. WP7 toolkit installation problems

I had a few headaches getting the toolkit to install, and it kept failing for some reason and I think they were related to not having VS Express (or whatever the free version is).
I don’t remember what I did exactly, but there are people who have workarounds and a few retries worked for me, for installing the XMA framework for example.

If you’re having an installation problem, look for the toolkit iso and shut down and even reboot and try again. If not, ask in the WP7 forum at create.msdn.com and hopefully you will get some help.

5. Consider the LongListSelector control for nested lists

I had a situation whereby I had a kind-of master-detail view shown together where the master items are shown with their details items next to them, for eg.

Master 1
      detail 1.1
      detail 1.2

Master 2
     detail 2.1

Master 3
    detail 3.1
    detail 3.2
    detail 3.3
    detail 3.4

I started with nested Listboxes but then realized that the ItemsControl is also a possibility since I did not need Listbox behavior like selection of items, etc.
Think of ItemsControl as the insides of a ListBox.

But then scrolling became an issue because I wanted all items to be visible at once and not need to scroll the detail list for item 3 for example.

Fyi, you can make the ItemsControl scrollable by adding a View Template, like so:

<ItemsControl x:Name="myItems">
 <ItemsControl.Template>
  <ControlTemplate TargetType="ItemsControl">
    <StackPanel>
      <ScrollViewer VerticalScrollBarVisibility="Auto" Margin="0,0,0,0">
	<ItemsPresenter />
      </ScrollViewer>
    </StackPanel>
  </ControlTemplate>
 </ItemsControl.Template>
</ItemsControl>
There are many nice posts about ItemsControl which you can look at to tweak and use them well.
Unfortunately, they couldn’t work easily for me, since I needed to autosize the nested details so that either 1 or 4 items could be shown without scrolling.
I say easily because I am sure sure some WPF gurus can do almost anything with ListBoxes, but not me.
I am now working to adapt the LongListSelector control from the toolkit. It was mainly made for virtualizing the View and the data to give you a fast scrolling and grouped list.
The Contacts list on the phone is a good example of it.
So, if you want to use nested lists and want the children to autosize, etc., look at the LongListSelector sample in the toolkit.
This mini-series by WindowsPhoneGeek helped me understand it better.

6. Re-entrancy problems are possible with MVVM Light
I am using the MVVM Light framework which is quite handy for locating ViewModels, but you also need to be careful about manipulating collections while in a loop.
This is more an issue of bad implementation than the framework itself, but iterating over static ViewModel is enticing and a common mistake and should be done with caution.
If you change any item in the List will throw an Exception. I forget now exactly, but I think I was getting a NullReferenceException.
So, my advice while manipulating a ViewModel List, is to create a new List and iterate over the static ViewModel List and copy it’s contents and then set the ViewModel list to your new local List.
Hope these points saved some of your time…

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