Abstracting the LicenseInformation Class

The downloadable sample code includes a custom ILicenseService interface, which contains a single property called Trial, indicating the trial state of the app. There are two implementations of this interface: one for testing and one for production.

The production implementation named LicensingService wraps a LicenseInformation instance, as shown in the following excerpt:

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public class LicensingService : ILicensingService
{
    public bool Trial
    {
        get
        {
            LicenseInformation licenseInformation
                                    = new LicenseInformation();
            return licenseInformation.IsTrial();
        }
    }
}

During development and testing, the LicensingService class is replaced by a MockLicensingService class, which allows you to change the value of its Trial property. See the following excerpt:

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public class MockLicensingService : ILicensingService
{
    bool trial = true;

    public bool Trial
    {
        get
        {
            return trial;
        }
        set
        {
            trial = value;
        }
    }
}

The particular implementation that is used depends on the type association within the IoC container. When the project is built using a release configuration, LicensingService is used; otherwise, the MockLicensingService is used.

Within the ChatClientView page is a button whose visibility depends on a viewmodel property called BuyOptionVisible. See the following excerpt:

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bool buyOptionVisible;

public bool BuyOptionVisible
{
    get
    {
        return buyOptionVisible;
    }
    private set
    {
        Assign(ref buyOptionVisible, value);
    }
}

In the viewmodel constructor, the value of the buyOptionVisible field is determined using the ILicensingService, which is resolved via the static Dependency method called Resolve:

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var licensingService = Dependency.Resolve<ILicensingService>();
buyOptionVisible = licensingService.IsTrial;

An AppBarMenuItem is bound to the BuyOptionVisible property, as shown:

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<u:AppBar.MenuItems>
    <u:AppBarMenuItem Text="Buy"
        Command="{Binding BuyCommand}"
        Visibility="{Binding BuyOptionVisible,
        Converter={StaticResource BooleanToVisibilityConverter}}" />
</u:AppBar.MenuItems>

A value converter is used to convert the Boolean value to a Visibility enum value.

When the user taps the button, the BuyCommand is executed. In the next section you see how the BuyCommand uses an abstracted MarketPlaceDetailTask to launch the built-in marketplace application on the phone.