Wednesday, December 29, 2010


Reusing the ViewModel in MVVM for WP7

Edit: There turned out to be a way to do this without having to deal with the warning message that appears from WP7 using a Silverlight Class Library. The altertive way retains the write once ViewModel, but compiles the ViewModel seperately in each project it's used in:

I am creating a game for the WP7 that I decided I wanted to be a pay to play game. One important step that became evident is the need for a trail version. I wanted the trail version to stay up to date with minimal effort as I update the rest of the game. To do this I decided to make use of the MVVM model, using a single ViewModel for both the View of the paid version and the View of the trail version.

I thought this seperation would be a daunting task as I had little experience creating multi-project solutions. However, this is surprisingly simple. The extreme simplicity of it explains why I was unable to find much information while searching the internet. Following are the steps I took.

  1. Install MVVM Light V3 Binaries and Templates for your flavor of Visual Studio

  2. Install the WP7 RTM hotfix

  3. If you did not unblock the MVVM binaries .Zip file before you installed you can either unblock that .Zip file now and reinstall (the recommend method) or individually unblock all of the installed MVVM Light binaries for WP7 and Silverlight 3.

    Location of the to Unblock button in a files properties

  4. Create a new MvvmLight (WP7) project with any name, I named if after a game I want to create called BouncyLasersMvvm.

    Creating a new MvvmLight (WP7) solution

  5. Add a Silverlight Class Library named “ViewModel” that is targeted to Silverlight Version 3. I choose Silverlight 3 because it is the CLR that WP7 uses.

    Add Silverlight Class Library project

  6. Click and drag the ViewModel Folder into the ViewModel Project to create a copy.

    Copy the ViewModel folder from the View project into the ViewModel project

  7. In the ViewModel Project Add a reference to all 3 GalaSoft MVVM libraries; "System.Windows.Interactivity.dll" "GalaSoft.MvvmLight.dll" and "GalaSoft.MvvmLight.Extras.dll"

    Add all of the MVVM Light libraries

  8. Delete the Model and ViewModel folders from the MVVM project and add a reference to the ViewModel project.

    Delete ViewModel data from the View Project

  9. In the App.xaml of the View project, change the value of xmlns:vm to
    [your solution name].ViewModel;assembly=ViewModel

  10. In the codebehind for the App.xaml, App.xaml.cs, change the last using statement, that should now have a red line beneath it, to use the same namespace you referenced in the App.xaml in step 9. In this example it would be using BouncyLasersMvvm.ViewModel

That’s it. If you’d like to create more Views add new MVVM Light projects. Then repeat steps 8 and 10. You can now make Views for trail versions or Views for demos to put on a website using silverlight.

When you modify the text used for the Welcome property inside of ViewModel/MainViewModel.cs and swap the project that is run using “Set as startup project” you will see that all the Views you create now use the same ViewModel.

Edit: Limitations of a Silverlight 3 ViewModel for WP7 (from
"You can reuse a Silverlight 3 Class Library between a web and WP7 project without any problems as long as you follow the following guidelines:

It's not as limiting as it sounds, in fact the entire Silverlight Toolkit is binary compatible between the web and WP7"

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Tuesday, December 28, 2010


Getting MVVM Light to work with WP7

I ran into several issues while getting MVVM Light V3 ( to work with VS 2010 ver 10.0.30319.1 and the first Release version of WP7 Tools.
The major difference is the Navigation namespace is now inside the Microsoft.Phone.Controls namespace.

Following are the steps I took to add an MVVM Light WP7 project to run.

Changes to Project References
Add reference to

remove refrence to

Changes to WMAppManifest.xml
the "L" in silverlight is no longer a capital letter, Change case of RuntimeType value to

remove instance of
PlaceHolderString="Default task"

Changes to Permissions on .dll's
Error messages may pop up saying .dll's are flagged from being downloaded from the web.
-Navigate to the files in explore
-right click an offending file
-select properties
-on the "General" tab click "Unblock" near the bottom.

Changes to App.xaml
remove from App.xaml

Source="/MainPage.xaml" />

Add to App.xaml.cs
the usings
using Microsoft.Phone.Controls;
using System.Windows.Navigation;

public App()
...keep code already in there and add lines below
// Phone-specific initialization
#region Phone application initialization
/// Provides easy access to the root frame of the Phone Application.

/// The root frame of the Phone Application.
public PhoneApplicationFrame RootFrame { get; private set; }

// Avoid double-initialization
private bool phoneApplicationInitialized = false;

// Do not add any additional code to this method
private void InitializePhoneApplication()
if (phoneApplicationInitialized)

// Create the frame but don't set it as RootVisual yet; this allows the splash
// screen to remain active until the application is ready to render.
RootFrame = new PhoneApplicationFrame();
RootFrame.Navigated += CompleteInitializePhoneApplication;

// Handle navigation failures
RootFrame.NavigationFailed += RootFrame_NavigationFailed;

// Ensure we don't initialize again
phoneApplicationInitialized = true;

// Do not add any additional code to this method
private void CompleteInitializePhoneApplication(object sender, NavigationEventArgs e)
// Set the root visual to allow the application to render
if (RootVisual != RootFrame)
RootVisual = RootFrame;

// Remove this handler since it is no longer needed
RootFrame.Navigated -= CompleteInitializePhoneApplication;

// Code to execute if a navigation fails
private void RootFrame_NavigationFailed(object sender, NavigationFailedEventArgs e)
if (System.Diagnostics.Debugger.IsAttached)
// A navigation has failed; break into the debugger

Changes to MainPage.xaml


change phoneNavigation:PhoneApplicationPage to phone:PhoneApplicationPage on both the top of the page and the bottom

Edit: This didn't fix everything, there are issues such as the ListViewItem being replaced by the ListBoxItem. I recommend following the link Laurent Bugnion commented below, where he's already done all the work for us. If you're really curious of all the changes do a diff between the templates.

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Thursday, December 09, 2010


Multiple-Key down: 3 keys held down, 2 show up

When holding down multiple keyboard keys some keys may not register. You can test your keyboard by doing the following.

1. Open up a text editor (MS Word, Notepad or vi)
2. Hold the UP ARROW
3. Hold the LEFT ARROW
4. Keep those held and now press the SPACEBAR

If you did happen to see a space show up, your keyboard likely cost a pretty penny. Most people, however, use the cheapest keyboard they can get. This "No Space shows up" error is called "Masking" or "Ghosting" and is explained throughly here:

Some keyboard manufacturers worked around this by moving where the Masking happens. For example, some keyboards don't show a space bar press if you're already holding down S and D.

The best work around for this issue when developing software that utilizes multiple keys(such as games) is to either allow the user to assign keys or map two sets of keys to each software event. For example, allow them to use WASD instead of the Arrow keys.

Original source: http://www.­tage7.­net/­devblog/­2010/­01/­17/­the-­multiple-­key-­down-­problem/­ google cached

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