All posts by Jeremy

Learn Model-View-ViewModel, LOB WPF/Silverlight application

WPF, ,

I’ve been waiting for a long time for this, and Karl Shifflet finally did it !

Karl is a WPF guru, and he just started a new series of articles on Model-View-ViewModel. Here is his own introduction: “My goal is to provide an introduction, several simple examples and progress to a series of WPF LOB scenarios where M-V-VM is used.  Scenarios like, dialog box, simple form, master – detail, complex master detail with several embedded ViewModels, etc.”

I’m sure this series will very soon become the reference to learn MVVM. His first article is about validating the user input in a concise and agile way. Right now, I can’t give more details because I just start to read the article, but I’ll try to give my feedback as soon as possible.

TransitionPresenter control from FluidKit

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By looking at Worpress statistics for my blog, I realized that many people were coming here by searching keywords like “animation”, “transition”, etc. A couple of month ago, I wrote an article about a control that I created: the ContentSlider control. The article described a control that could be used to create an animation when switching from one page to another, but it was very basic.

If you’re looking for a more complete solution, I recommend you to take a look at the FluidKit library created by Paven Podila. The FluidKit library contains very powerful control, the most known is probably the ElementFlow control that is similar to Apple’s famous CoverFlow functionality:

FluidKit also contains a TransitionPresenter control that is an extended and more powerful version of my ContentSlider control. The TransitionPresenter control comes with 4 transitions that you can easily use in your application (Cube, Flip, Slide, Genie):

Pavan really did a great job with the FluidKit library. Go ahead a grab the source to play with it and learn very cool stuff about WPF !

How insert Separator in a databound ComboBox

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As you might already know, I’m a big fan of the Model-View-ViewModel pattern. I’m using it extensively on the current I’m working on at work. Today I had to face a simple problem that was tricky to solve.

In the application I’m building, I have a “Library panel”. This panel contains a set of items that are used in my application. Because the number of items can be very large, I decided to add a filter capability. Filtering to a collection is very straightforward once you get familiar with the ICollectionView interface. If you want more details about it, check out Marlon’s blog post about it.

To give the user the possibility to filter the items, I added a ComboBox control. Of course, because I’m using the MVVM pattern, I’m not creating the ComboBoxItem myself, the databinding mechanism of WPF handle this (to be precise, the databinding handles collecting the item, and the ComboBox handles the creation of the ComboBoxItem to wrap them…).

The problem

In my ViewModel, I create a ObservableCollection<string> property that I called “Categories”.Then, in my view (XAML), I databound the ComboBox’s ItemsSource property to this “Categories”. Ok, it works fine and took me about 10min to do it.

Now, I want to add separator between some ComboBoxItem… Hmmm, how should I do that… I cannot do combobox.Items.Add(something) anymore because the ItemsSource property is databound… Well, I could as something in my ViewModel, but what ?

My solution

I wanted to keep the logical information about where Separator are in the ViewModel. This is typically an example of something that should stays in the ViewModel. I decided to add an empty items in my ObservableCollection for every Separator I wanter to have in the view.

In the view, I set up an ItemContainerStyle for my ComboBoxItem. The tricky part is, how could I replace my ComboBoxItem with a Separator… Well actually, we can’t. But what we can do is to change the entire template of the ComboBoxItem when the content is empty:

And voila ! It works fine and keeps the logic in the ViewModel. If you have any other idea about how we can solve this issue, please feel free to comment 🙂