Usually, having price as a double value is a very bad mistake. However, in some cases this is necessary, for example when your analytic system requires it, like Amazon Mobile Analytic does. Both Android and iOS provide you with a way to get that information, but Windows (Phone) Store only gives you FormattedPrice string.

And obvious way to get price value from it is to use CurrencyFormatter class provided by Microsoft. However, things are not quite that simple. The biggest question is which locale Store used to create FormattedPrice for you. The answer is a little complicated. It pulls currency (and its symbol) from one place, but it takes formatting (including placement of currency symbol relative to value and thousands separator) from another.

If you create CurrencyFormatter with only currency identifier, it will not be able to parse FormattedPrice in all cases, when user have set different regional settings in different places (for example, if he uses USA store with USD as currency, but his price formatting is done in British style) or if he set up some custom formatting.

So instead we need to use the second constructor. It takes a list of languages, and ID of geographical region. It might not be obvious how it can help our cause, but actually specifying this information allows CurrencyFormatter to pull formatting properties set up for user’s language and use them instead of defaults. However, exactly how it does it is not clear from documentation. Our own testing showed that the last parameter (geographical region ID) does not matter – you can always pass in “US”, but the key is to pass user’s language as the second parameter. Take this with a grain of salt, please: until we know the third parameter NEVER does affect parsing, we need to be cautious about it…

The only remaining question is how to get the locale used by Store. The only answer I found works only in C++ using old WinAPI functions, so it’s only relevant for those who target desktop Windows, or Windows Phone 8.1+ and use C++ to interact with Store. Fortunately, that’s just what we do at work 🙂 So, here’s the final code to get price value from FormattedPrice in Windows Store in C++:

// Assuming we're in LoadListingInformationByProductIdsAsync handler 
// and just successfully received ListingInformation
ApplicationModel::Store::ListingInformation^ listInfo = operation->GetResults(); 

// This gets us currency ID used by store, but language settings used for formatting
Windows::Globalization::GeographicRegion^ geographicRegion 
    = ref new Windows::Globalization::GeographicRegion(listInfo->CurrentMarket); 
Platform::String^ currencyID = geographicRegion->CurrenciesInUse->GetAt(0);

// Now, some WinAPI magic: get us user's default locale, which is used by Store to format things
WCHAR wcBuffer[10];
GetUserDefaultLocaleName(wcBuffer, 10);
Platform::String^ userFormatLocale = ref new Platform::String(wcBuffer);

// Use locale returned by GetUserDefaultLocaleName to populate 
// a list of languages for CurrencyFormatter
Platform::Collections::Vector<Platform::String^>^ v 
    = ref new Platform::Collections::Vector<Platform::String^>();
v->Append(userFormatLocale);

// Create CurrencyFormatter using the second form of constructor. 
// Please note that I'm NOT sure about meaning of the 3rd parameter!
Windows::Globalization::NumberFormatting::CurrencyFormatter^ formatter 
   = ref new Windows::Globalization::NumberFormatting::CurrencyFormatter(currencyID, 
         v, ref new Platform::String(L"US"));

// Iterate over products in listInfo
for (auto iter : listInfo->ProductListings)
{
    ApplicationModel::Store::ProductListing^ store_product = iter->Value;
                
    // Use formatter to parse currency value into double. 
    // A Decimal might be preferable for anything serious, but for statistics it will have to do
    Platform::IBox<double>^ result = formatter->ParseDouble(store_product->FormattedPrice);

    // In case formatter failed to parse the price, to a check
    double price = result == nullptr ? 0.0f : result->Value;  
}

There you have it. This solution is not without magic components which may fail, but it seems to work in most cases. Please remember, that you DON’T need this most of the time – a price representation in string format should suffice for almost ANY case! But if you really, really need to parse FormattedPrice into double value – there you have it.

Since Google hates C++ developers and still haven’t finalized NDK support in Android Studio, we at Lextre call ndk-build manually, by using task( type: Exec ) in Gradle. However, we need to pass some parameters to it. For example, different build variants must use different output directories for object files, and we also need to set various flags depending on whether we are building debug or shipping configuration.

In general, it seems to be useful to know how to parametrize tasks based on chosen build variant (which is a combination of build configuration and product flavor).

The obvious solution – to create some variables in build.gradle and use them in task’s body – won’t work, because variables are computed and substituted during configuration step, while we only know the chosen build variant in build step.

The second obvious solution is to use project properties, which you can specify via -P key when running Gradle from command line. However, this is very inconvenient: we already specify build variant, which should tell Gradle everything it needs to know. Also, it would make building from Android Studio harder, if no impossible.

The problem is that the task’s configuration is immutable after the configuration step is complete. So, the solution is to have a different task for every build variant, each with its own configuration! Of course, to write them all by hand is a thing no sane person should do, especially as the number of build variants grow very fast with each added configuration or product flavor. Therefore, we need to automate task creation.

Gradle has a mechanism for that: Rules. Unfortunately, I haven’t managed to get it working. On the other hand, it looks pretty much the same as the solution I finally devised.

So, instead of Rules, I do this: Gradle allows you to iterate over the set of already-present tasks. I use this feature to find all tasks that compile a concrete build variant, and create a new task with an unique name and configuration, than make the old task depend on the new one. Without further delays, here’s the code:

tasks.withType(JavaCompile) {
        compileTask -> 
              // NDK task name
            def ndkBuildTaskName = "ndkBuild_" + compileTask.name
            
              // NDK task parameters
            def obj_dir = "../../build/ndk/";
            def debug = 0;
            def shipping = 0;
            def km = 0;
            
              // Parse build configuration. If it's an umbrella task (which includes several configurations), skip it
            if ( compileTask.name.contains("Debug") )
            {
                obj_dir += "obj_debug";
                debug = 1;
            }
            else if ( compileTask.name.contains("Release") )
                obj_dir += "obj_release";
            else if ( compileTask.name.contains("Shipping") )
            {
                obj_dir += "obj_shipping";
                shipping = 1;
            }
            else
                return;
            
              // Parse product flavor. If there isn't one, skip this task
            if ( compileTask.name.contains("Google") )
                obj_dir += "_google";
            else if ( compileTask.name.contains("Amazon") )
                obj_dir += "_amazon";
            else if ( compileTask.name.contains("Km") )
            {
                obj_dir += "_km";
                km = 1;
            }
            else
                return;
            
              // Create a new NDK task with specified name
            tasks.create( ndkBuildTaskName, Exec ) {
                  // Set parameters to be used in Android.mk
                if ( shipping == 1 )
                    environment( "SHIPPING", "-DSHIPPING" );
                if ( debug == 1 )
                    environment( "DEBUG", "1" );
                if ( km == 1 )
                    environment( "PS_RU", "-DPS_RU" );

                  // Enable maximum safe number of cores for parallel builds
                int cores = Runtime.getRuntime().availableProcessors();
                int ndkThreads = cores > 1 ? cores - 1 : 1;
                if ( project.hasProperty('NDK_THREADS') ) {
                    ndkThreads = Integer.parseInt(NDK_THREADS)
                }
                
                  // Find ndk-build command
                def ndkRun = 'ndk-build'
                if ( project.hasProperty('NDK_RUN') ) {
                    assert file(NDK_RUN).exists()
                    ndkRun = NDK_RUN
                } else if (Os.isFamily(Os.FAMILY_WINDOWS)) {
                    ndkRun += '.cmd'
                }

                  // Run ndk-build. We have our .mk files in src/main/jni, but you may have them in some other location
                  // NDK_OUT specifies directory for object files. If not specified, it will always be 'obj' 
                  // and it will break debug/release/shipping switch
                commandLine ndkRun, '--jobs', ndkThreads, '-C', file('src/main').absolutePath, "NDK_OUT=$obj_dir"
            }
            
              // Make java compilation task depend on newly created task
            compileTask.dependsOn ndkBuildTaskName
    }

I’ll be the first to admit that this might not be the most elegant solution, but still, it works and it’s flexible enough. If you know a better way to solve this problem, I urge you to share it in comments, because I searched Google in vain for one before, and haven’t found anything.