Windows 8 C# code sample that asks for a review of the app after 5 launches per app version

example.cs

// -------------------------------------------------------------------
// Ask for a review after 5 starts of a new version of the Application
// -------------------------------------------------------------------

// Variable to hold the number of time the app started
int startedCount = 0;
// Variable to hold if the user actually accepted to rate the application
bool reviewedBefore = false;
// Variables to hold the current and the last version number that was started in a string
string currentVersion = string.Format("{0} - {1} - {2} - {3}", Package.Current.Id.Version.Major,
    Package.Current.Id.Version.Minor, Package.Current.Id.Version.Build, Package.Current.Id.Version.Revision);
string lastVersionStarted = currentVersion;

// Check if the variables were stored in the Roaming Settings before loading them
if (Windows.Storage.ApplicationData.Current.RoamingSettings.Values.ContainsKey("startedCount"))
{
    // If so, read it in the variable
    startedCount = (int)Windows.Storage.ApplicationData.Current.RoamingSettings.Values["startedCount"];
}
if (Windows.Storage.ApplicationData.Current.RoamingSettings.Values.ContainsKey("reviewedBefore"))
{
    // If so, read it in the variable
    reviewedBefore = (bool)Windows.Storage.ApplicationData.Current.RoamingSettings.Values["reviewedBefore"];
}
if (Windows.Storage.ApplicationData.Current.RoamingSettings.Values.ContainsKey("lastVersionStarted"))
{
    // If so, read it in the variable
    lastVersionStarted = (string)Windows.Storage.ApplicationData.Current.RoamingSettings.Values["lastVersionStarted"];
}

// If the current version is equal to the last version started
if (currentVersion.Equals(lastVersionStarted))
    // Increment the started count by 1
    startedCount++;
else
    // Reset the count because the new version might have fixed some problems or be better
    startedCount = 0;

// And then save the variables in the Roaming Settings. Note that if the value pair was not
// created before, the method will create it automatically
Windows.Storage.ApplicationData.Current.RoamingSettings.Values["startedCount"] = startedCount;
Windows.Storage.ApplicationData.Current.RoamingSettings.Values["lastVersionStarted"] = currentVersion;

// If the app was started 5 times
if (startedCount == 5)
{
    // Change the msg based on the fact that the application was reviewed before or not.
    string msg;
    if (!reviewedBefore)
        msg = "Thank you for using [App Name] for a while now, would you like to review this app?";
    else
        msg = "Thank you for your ongoing use of [App Name]. We made changes since the last time you were asked to review it. Would you mind telling us what you think again?";

    // Create a MessageDialog requesting a review
    var md = new Windows.UI.Popups.MessageDialog(msg, "Please review my app");
                
    // Build the 3 potential responses using the Commands collection
    // If they say yes, send them to the store
    md.Commands.Add(new Windows.UI.Popups.UICommand(
        "Yes", 
        new Windows.UI.Popups.UICommandInvokedHandler(async (cmd) => {
                // Find the FamilyName of the app package
            string familyName = Package.Current.Id.FamilyName;
            // Navigate to the store Review Page for the Application
            // *** Note that the next line will launch the store app but will not find your app until
            // *** it is published.
            await Windows.System.Launcher.LaunchUriAsync(new Uri(string.Format("ms-windows-store:REVIEW?PFN={0}", familyName)));

            // Change the status to track the fact that they agreed to a review
            reviewedBefore = true;                   
            // Store the reviewedBefore variable in local storage
            Windows.Storage.ApplicationData.Current.RoamingSettings.Values["reviewedBefore"] = reviewedBefore;
        })));
    // If they say no, just close the dialog box
    md.Commands.Add(new Windows.UI.Popups.UICommand(
        "No",
        new Windows.UI.Popups.UICommandInvokedHandler((cmd) => { })));
    // If they say ask later, reset the count to 0 giving a grace period of 5 again
    md.Commands.Add(new Windows.UI.Popups.UICommand(
        "Ask Later",
        new Windows.UI.Popups.UICommandInvokedHandler((cmd) => {
            startedCount = 0;
            Windows.Storage.ApplicationData.Current.RoamingSettings.Values["startedCount"] = startedCount;
        })));

    // Display the MessageBox asyncronously. ** Note that you may have to add the async keyword to
    // the OnLaunched event definition above
    await md.ShowAsync();
}