Solution for: “Another user has already installed a packaged version of this app. An unpackaged version cannot replace this”

After resetting the data for my app locally and then deleting it I encountered the following error: “DEP0700 : Registration of the app failed. Another user has already installed a packaged version of this app. An unpackaged version cannot replace this. The conflicting package is xxx and it was published by CN=xxx.”

For some reason the app was still on the system for another user. I ended up having to run powershell as an administrator and running the following snippet to delete the app completely from the system:

get-appxpackage -all | where name -eq “” | remove-appxpackage

A numeric comparison was attempted on TargetPlatformVersion evaluated to empty string

So after upgrading to Visual Studio 2013 update 1 and upgrading my web project to MVC 5.1 I could no longer load or build the project. I keep getting an error from MSBuild stating that the TargetPlatformVersion variable evaluated to an empty string. Naturally this caused some initial headache.

After comparing the project file with a clean project and finding no major differences I moved on to looking at the solution file. It turns out the VisualStudioVersion had been bumped to “12.0.30110.0” up from the previous “12.0.21005.1”. After updating this to the newest version the project successfully loaded again.

So if you experience this issue update your solution files visual studio version and reload the solution.

Let User Clear ComboBox Selection

The built-in ComboBox for Windows 8 does not come with a way to revert the control back to an unselected state. This is an issue in the scenario where the value in the ComboBox isn’t required an thus needs to be clearable.

A simple solution is to add an extra item to the Combox without any text and a value of -1. We can then wire up the CB with an attached property and handle the SelectionChanged event. Whenever we see a value of -1 being selected we can clear the selection.

One of the pros of clearing the CB is the placeholder text. Upon clearing the selection the placeholder text reappears.

The sample attached property can be seen below

public class ComboBoxHelper : FrameworkElement

public static bool GetClearOnEmptyValueSelection(DependencyObject obj)
 return (bool)obj.GetValue(ClearOnEmptyValueSelectionProperty);

public static void SetClearOnEmptyValueSelection(DependencyObject obj, bool value)
 obj.SetValue(ClearOnEmptyValueSelectionProperty, value);

public static readonly DependencyProperty ClearOnEmptyValueSelectionProperty =
DependencyProperty.RegisterAttached("ClearOnEmptyValueSelection", typeof(bool), typeof(ComboBoxHelper), new PropertyMetadata(false, (o, args) =>
 var cb = (ComboBox)o;

 if ((bool)args.NewValue)
  cb.SelectionChanged += (sender, eventArgs) =>
   if (eventArgs.AddedItems.Count == 1)
    if (cb.SelectedValue == null || string.IsNullOrWhiteSpace(cb.SelectedValue.ToString()) || (cb.SelectedValue is int && (int)cb.SelectedValue == -1))
     cb.SelectedIndex = -1;


With the attached property at hand wiring the CB is as simple as:

<ComboBox ap:ComboBoxHelper.ClearOnSelection="true">

Portable Libraries at Campus Days 2013

I will speaking at Campus Days 2013 Wednesday at 10:15 in the Developer track.

This year I will cover Portable Class Libraries (PCL) in .NET.

The talk will briefly introduce the new features and the foundation it is built upon. The main focus of the presentation will be an exploration of the possible and most popular use cases for PCLs. This includes building a clean api, sharing api entities, sharing platform features and sharing view models (in MVVM).

It will be a light presentation. Hope to see you there.

‘The app didn’t start’ Issue

I was presented with this error message upon launching my newly upgraded 8.1 Windows Store app. In the process of upgrading I also upgraded all the related Nuget packages. What I didn’t see was that one of the packages added an App.config file to my Windows Store project.

One hour later…

apparently this App.config causes the app to crash upon activation with no additional information.

Solution: Delete the App.config file from your store project.