30 September 2016 UWP, WPF, DesktopAppConverter, Centennial Robert Muehsig

Project Centennial - running desktop apps in the UWP world

Last year Microsoft revealed the plans to run and distribute desktop apps (basically all apps ever written for Windows) in the Universal-Windows-Platform “universe”. The project titel was “Project Centennial” and a year later the tooling seems to be ok-ish. So, let’s try something simple and convert a simple WPF app to UWP.

Limitations with this approach

Be aware that even if you can “convert” your WPF app this way you will get a UWP-ish app. The executable will only run on a normal Windows Desktop System. The app will not work on a Windows Phone, Xbox or HoloLens - at least not now.

Also keep in mind that certain operations might fail and that the outcome of some operations might suprise you. The app itself will run in a kind of sandbox. Calls to the file system or registry will be faked. Details can be found here.

As far as I know from a couple of hours playing around:

  • Changes to the Registry will not leak out of the sandbox, but for the app it will be seen as ok and is persistent
  • Changes to Well-Known-Folders (e.g. %AppData%) will not leak out of the sandbox, but for the app it will be seen as ok and is persistent
  • Some operation can leak out to the actual desktop, e.g. start another programm.

The Desktop App Converter

If you have an existing installer or setup you might want to take a look at the [desktop app converter](https://msdn.microsoft.com/en-us/windows/uwp/porting/desktop-to-uwp-run-desktop-app-converter. This utility will convert the installer to a UWP package.

A quick walk through can be found on Mike Taultys blog.

Step by Step - from WPF source to UWP app

The important steps from the WPF app to a UWP app are also documented in the MSDN.

But let’s start with a simple WPF app (running on .NET 4.6.1) - this is the MainWindow.xaml

<Window x:Class="WpfToUwpTestApp.MainWindow"
        Title="MainWindow - WpfToUwpTestApp" Height="350" Width="525">
        <Button Height="100" Width="100" Click="Button_Click1">Write in Registry</Button>
        <Button Height="100" Width="100" Click="Button_Click2">Write in AppData</Button>
        <Button Height="100" Width="100" Click="Button_Click3">Open HTTP Address</Button>


The code behind:

public partial class MainWindow : Window
    public MainWindow()

    private void Button_Click1(object sender, RoutedEventArgs e)
        RegistryKey key = Registry.CurrentUser.OpenSubKey("Software", true);

        key = key.OpenSubKey("WpfToUwpTestApp", true);

        key = key.OpenSubKey("ItWorks", true);

        key.SetValue("ItWorks", "true");

    private void Button_Click2(object sender, RoutedEventArgs e)
        string roaming = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);

        string appFolder = System.IO.Path.Combine(roaming, "WpfToUwpTestApp");

        string file = System.IO.Path.Combine(appFolder, "Test.txt");

        if (Directory.Exists(appFolder) == false)

        File.WriteAllText(file, "Hello World!");

    private void Button_Click3(object sender, RoutedEventArgs e)

Pretty simple, right? Those three operations came just to my mind. In general I wouldn’t use the Registry at all, but I had a use case in mind where I need to access the Registry.

I also added a couple of dummy store images (from the default UWP app project template) - my solution looks like this:


When we build the .csproj the output should look like this:

  • WpfToUwpTestApp.exe
  • appxmanifest.xml
  • Assets/StoreLogo.png
  • Assets/Square150x150Logo.scale-200.png
  • Assets/Square44x44Logo.scale-200.png

The appmanifest.xml

The next step is to create the appmanifest.xml - on the MSDN there is a handy template. The Desktop App Converter does the same thing and tries to create this file automatically, but it’s not that hard to set it by hand:

<?xml version="1.0" encoding="utf-8"?>
  <Identity Name="WpfToUwpTestApp"
    Version="" />
    <Description>No description entered</Description>
    <Resource Language="en-us" />
    <TargetDeviceFamily Name="Windows.Desktop" MinVersion="10.0.14316.0" MaxVersionTested="10.0.14316.0" />
    <rescap:Capability Name="runFullTrust"/>
    <Application Id="Test" Executable="WpfToUwpTestApp.exe" EntryPoint="Windows.FullTrustApplication">
       Description="WpfUwpWriteInRegistry - Desc" />

Create the App.appx package

Now we are ready to create the appx package. You need the Windows 10 SDK to do this.

To simplify things, I copied the needed files from the build output to a folder called _App.

To create the package, invoke the following command:

"C:\Program Files (x86)\Windows Kits\10\bin\x64\makeappx.exe" pack -d "%~dp0_App" -p "%~dp0App.appx"

The result is a unsigned appx package called “App”.

Create a valid pfx (one time only)

In the following step we need a valid pfx to sign the package. For development you can use this command to create a pfx:

"C:\Program Files (x86)\Windows Kits\10\bin\x64\makecert.exe" -r -h 0 -n "CN=Robert" -eku -pe -sv App.pvk App.cer 

"C:\Program Files (x86)\Windows Kits\10\bin\x64\pvk2pfx.exe" -pvk App.pvk -spc App.cer -pfx App.pfx -po apptest

After this you should see a “App.pfx” in the folder. I’m not 100% sure if this step is really needed, but I needed to do it, otherwise I couldn’t install the app:

Now click on the pfx and enter the password “apptest” and import it in the “Trusted Root CAs”:


Sign App.appx

Now we need to sign the package and we are done:

"C:\Program Files (x86)\Windows Kits\10\bin\x64\signtool.exe" sign /f "App.pfx" -fd SHA256 /p apptest "App.appx"

Install the App!

Now you can double click on the appx package and the installer will show up:


Running the App

And there is our beauty:


Exploring the sandbox:

Remember our 3 methods? The results of those three calls are:

  • Write to the Registry: Seems to work for the app, but (as expected) the registry value will not leak out of the “sandbox”
  • Write to %appdata%: Seems to work for the app, but the data value will not leak out of the “sandbox”
  • Open a browser: The default browser will be invoked for a HTTP url.

It was my first try to convert a (simple) WPF app to UWP and the result is interesting.

Hope my first steps in this world might help you!

The code and a handy readme.txt is available on GitHub.

From the comments: Fun with registy.dat files:

James Hancock/John Galt discovered a nice registy trick. His goal was to “fake” a given registry key, so that the converted UWP app can see a “virtual” registry key. This can be done with a file named “registry.dat”.

The registry.dat seems to be the source and target of all write actions inside the app:

“The virtual registery is always the registry.dat. if you don’t provide a default version then one is created on first use for you.

But if you do, then yes you can deploy whatever entries you want as a starting point for your app otherwise the starting point is whatever that computer currently has in the real registry.”

You can create such registry.dat files via RegEdit & export it as registry hive. Be aware, that my test run wasn’t successful, but I hope to get working sample. Until that I hope James comments will be helpful.

Written by Robert Muehsig

Software Developer - from Dresden, Germany, now living & working in Switzerland. Microsoft MVP & Web Geek.
Other Projects: ExpensiveMeeting | EinKofferVollerReisen.de

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