Getting full control over MSIX updates with the App Installer APIs
Published May 13 2022 07:59 AM 3,954 Views
Microsoft

App Installer is a powerful technology which enables to streamline the deployment and update of applications packaged with MSIX. Thanks to App Installer, you can enable features which are typically reserved only to managed deployment platforms (like the Microsoft Store or Endpoint Manager), for instance automatic updates. By setting up the App Installer file in the proper way, you can let Windows automatically check the availability of updates and install them without any extra effort from the developer. It's enough to publish an updated version of the package on the original location (a website or a network share) to let Windows download and install it, based on the logic you have defined in the App Installer file (you can check for updates in background, when the application is launched, etc.).

This approach is great for many scenarios, especially the ones in which you don't have access to the source code (for example, you're a system administrator managing the deployment of apps for the company). However, if you're a developer who is actively building and evolving your application, you might want more control over the update process. For instance, you may want to tell the user, within the application itself, if there's an update available.

To support these scenarios, the Windows Runtime comes with a series of APIs that you can use to interact with App Installer: if your MSIX packaged application has been deployed using an App Installer file, you can leverage these APIs to perform tasks like checking if an update is available, triggering the update, etc.

Let's explore this scenario in more detail.

Checking for an available update

The heart of these APIs is the Package class, which belongs to the Windows.ApplicationModel namespace. This is a Windows Runtime namespace, so to access it you might need to make a few tweaks to your project based on the UI platform you've chosen:

  • If it's a UWP or WinUI app built using Windows App SDK, then you're good to go. Both technologies offer built-in access to Windows Runtime APIs.

  • If it's a WPF or Windows Forms application based on .NET Framework or .NET Core 3.x, you must install a dedicated NuGet package.

  • If it's a WPF or Windows Forms application based on .NET 5 or .NET 6, you must set in the project's properties one of the target frameworks dedicated to Windows 10/11, like in the following sample:

     

    <TargetFramework>net6.0-windows10.0.19041</TargetFramework>
    

Now you can use the following code snippet to check if an updated version of the package is available via App Installer:

 

public async Task CheckForUpdates()
{
    Package package = Package.Current;
    PackageUpdateAvailabilityResult result = await package.CheckUpdateAvailabilityAsync();
    switch (result.Availability)
    {
        case PackageUpdateAvailability.Available:
        case PackageUpdateAvailability.Required:
            //update is available
            break;
        case PackageUpdateAvailability.NoUpdates:
            //no updates available
            break;
        case PackageUpdateAvailability.Unknown:
        default:
            break;
    }
}

The code is simple. First, we get a reference to the current package, using the Package.Current singleton. This object will enable us to access all the properties related to the MSIX package and the identity of the application. Then we call the CheckUpdateAvailabilityAsync() method, which will return us a PackageUpdateAvailabityResult object, that includes an Availability property which is an enumerator. If we get Available or Required, it means there's an update available. As you can see, we don't have to specify the URL where to check the update availability from. The API will automatically use the App Installer URL which is linked to the application. Windows automatically stores this connection when we install a MSIX packaged application through an App Installer file.

Thanks to this code, we can implement our own logic to communicate the information to our users: we can display a pop-up or a notification, we can tell them to restart the app so that Windows will download and install the update, etc.

But what if you want to take full control of the update process as well? Let's see how we can do it!

 

Installing the update from code

The App Installer APIs enables us not just to check if an update is available, but also to install the update. This feature can be used as a companion of the automatic feature provided by App Installer or independently.

  • In the first scenario, you will light up the App Installer APIs but, at the same time, you will define update rules in the App Installer file, like in the following example:

    <?xml version="1.0" encoding="utf-8"?>
    <AppInstaller
        xmlns="http://schemas.microsoft.com/appx/appinstaller/2021"
        Version="1.0.0.0"
        Uri="http://mywebservice.azurewebsites.net/appset.appinstaller" >
    
        <MainBundle
            Name="Contoso.MainApp"
            Publisher="CN=Contoso"
            Version="2.23.12.43"
            Uri="http://mywebservice.azurewebsites.net/mainapp.msixbundle" />
    
        <UpdateSettings>
            <OnLaunch 
                HoursBetweenUpdateChecks="12"
                UpdateBlocksActivation="true"
                ShowPrompt="true" />
            <AutomaticBackgroundTask />
            <ForceUpdateFromAnyVersion>true</ForceUpdateFromAnyVersion>
        </UpdateSettings>
    
    </AppInstaller>
    

    In this scenario, you can check for updates and install them using the APIs, but Windows will try also to apply updates automatically based on the logic you have defined in the App Installer file (like when the application starts or in background).

  • In the second scenario, you won't have any UpdateSettings section in the XML file, which will simply look like this:

    <?xml version="1.0" encoding="utf-8"?>
    <AppInstaller
        xmlns="http://schemas.microsoft.com/appx/appinstaller/2021"
        Version="1.0.0.0"
        Uri="http://mywebservice.azurewebsites.net/appset.appinstaller" >
    
        <MainBundle
            Name="Contoso.MainApp"
            Publisher="CN=Contoso"
            Version="2.23.12.43"
            Uri="http://mywebservice.azurewebsites.net/mainapp.msixbundle" />
    
    </AppInstaller>
    

    Windows will never try to update the application automatically, so you're in full control of the update process.

Let's see now the code we can use to download and install the update:

 

private async Task InstallUpdate()
{
    var pm = new PackageManager();
    var result = await pm.RequestAddPackageByAppInstallerFileAsync(new Uri("http://mywebservice.azurewebsites.net/appset.appinstaller"),
                        AddPackageByAppInstallerOptions.ForceTargetAppShutdown, pm.GetDefaultPackageVolume());
            
    if (result.ExtendedErrorCode != null)
    {
        txtUpdateStatus.Text = result.ErrorText;
        logger.Error(result.ExtendedErrorCode);
    }
}

First, we create a new instance of the PackageManager class, which belongs to the Windows.Management.Deployment namespace. Then we call the RequestAddPackageByAppInstallerFileAsync() method, passing as parameters

  • The URL of your App Installer file (yep, this time we need to specify it, unlike when we were checking for updates).
  • The behavior we want to achieve when the update is downloaded. There are a few options, but unfortunately the only one which is applicable is ForceTargetAppShutdown, which means that the application will be closed so that the update can be applied.
  • The folder where to install the update. By calling the GetDefaultPackageVolume() method of the PackageManager class, we get a reference to the default folder where MSIX packages are deployed.

You get back a DeploymentResult object as a result which, however, doesn't tell you much about the operation status. Remember, in fact, that if the update is successful, the application will be downloaded and reinstalled. In case of issues, however, the object will contain an ExtendedErrorCode property which, despite the name, contains a full Exception object with all the details about what went wrong.

Pay attention that the way the update process works might be highly disruptive for the user. After calling the RequestAddPackageByAppInstallerFileAsync() method, Windows will forcibly close the application to enable the update process to complete, without any warning message. As such, before calling it, make sure to save any data that the user might be working with and provide a clear message to the user to notify him about what's going to happen.

 

Tracking the progress of the update operation

To improve the user experience, you might want to at least display to the user the download progress, especially if the update is big. For this purpose, the RequestAddPackageByAppInstallerFileAsync() method doesn't return a standard IAsyncOperation object, but an IAsyncOperationWithProgress one. This means that we can use the following code to track progress:

private async Task InstallUpdate()
{
    var pm = new PackageManager();
    var deploymentTask = pm.RequestAddPackageByAppInstallerFileAsync(new Uri("http://mywebservice.azurewebsites.net/appset.appinstaller"),
                        AddPackageByAppInstallerOptions.ForceTargetAppShutdown, pm.GetDefaultPackageVolume());
            
    deploymentTask.Progress = (task, progress) =>
    {
        logger.Info($"Progress: {progress.percentage} - Status: {task.Status}");
        Dispatcher.Invoke(() =>
        {
            txtUpdateProgress.Text = $"Progress: {progress.percentage}";
        });

    };

    var result = await deploymentTask;
    
    if (result.ExtendedErrorCode != null)
    {
        txtUpdateStatus.Text = result.ErrorText;
        logger.Error(result.ExtendedErrorCode);
    }
}

The first key difference is that we have removed the await keyword before calling the RequestAddPackageByAppInstallerFileAsync() method. This means that we aren't immediately starting the operation, but we are simply storing a reference to the asynchronous operation we want to execute. Then we subscribe to the Progress event, which is triggered every time the status of the download changes. We can use the progress parameter to determine the status of the operation, through the percentage property. Once we have defined the handler, we can start the operation, by invoking the task again, this time with the await prefix.

There's a catch, however. The API doesn't return an update in real time, but only after a certain amount of time. As such, if the size of the update isn't big enough, you might not see any actual progress being returned. You will see the Progress event being triggered only at the beginning and at the end. This can be a common scenario when you use MSIX as a packaging technology. Remember, in fact, that MSIX supports differential updates, so even if the updated package is big, Windows will download only the files which changed.

If you want to provide a better user experience, there's a nice workaround that you can adopt and that was suggested by one of my customers during an engagement: downloading and launching the update App Installer file. This way, you'll continue to use the App Installer APIs to check for available updates, but the update process will be managed by Windows with the traditional App Installer UI, like in the following image:

 

external-appinstaller.png

 

This is how you can change the code to support this scenario:

private async void OnInstallUpdate(object sender, RoutedEventArgs e)
{
    HttpClient client = new HttpClient();
    using (var stream = await client.GetStreamAsync("http://mywebservice.azurewebsites.net/appset.appinstaller"))
    {
        using (var fileStream = new FileStream(@"C:\Temp\app.appinstaller", FileMode.CreateNew))
        {
            await stream.CopyToAsync(fileStream);
        }
    }

    try
    {
        var ps = new ProcessStartInfo(@"C:\Temp\app.appinstaller")
        {
            UseShellExecute = true
        };
        Process.Start(ps);
    }
    catch (Exception exc)
    {
        logger.Error(exc);
    }
}

First, using the HttpClient class, we download the most recent version of the App Installer file from our server, and we store it on the computer. Then, by using the Process.Start() API in .NET, we launch the file we have just downloaded, which will trigger the App Installer UI to show up and start the update.

The suggestions I shared with you before still apply, however. The UX will be indeed more polished, but the application will continue to be terminated once the update process is completed. As such, make sure to save all the data and notify the user about what's going to happen.

 

Updating an application without changing the code

What if you are interested in using the App Installer APIs to have more control over updates, but you don't want to change the code of your main application? This is a common scenario when you still need to distribute your app with a traditional installer technology, and you don't want to make code changes which are specific for MSIX deployment. In this case, you can leverage the fact that, inside a MSIX package, you can have multiple executables, which all share the same identity. Using the Windows Application Packaging Project, you can reference two different projects:

  • Your main application, which won't have any code change.
  • An updater application, which will use the APIs we have seen so far.

This is how the solution looks like in Visual Studio:

 

solution-explorer.png

 

Since both applications are packaged together, the App Installer API will work regardless of if they are called by the updater application or by the main application. Being another process, it's up to you how you want to invoke it. You might have a "Check for updates" option in the app that will invoke the updater application. Or you might have the updater application set as startup and check for updates every time the application starts. If no updates are found, the updater will close itself and launch the main application; otherwise, it will propose to the user to update the whole package.

The sample I've published on GitHub follows the second approach.

Wrapping up

In this article, we have seen how App Installer isn't just a technology for easily enable deployment and updates of Windows apps through a website or a network share, but also a set of APIs that we can use in our applications to get the best of both worlds: the benefits of MSIX and App Installer (like differential updates or the ability to manage dependencies) and the flexibility of having full control over the update process.

Happy coding!

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