Friday, January 31, 2014

No Biggie - How to Query the Available Storage Size in WinRT

Tape drive photo by P. Hollenback
The Windows Runtime (WinRT) provides a nice file IO API called Windows.Storage. Part of it are atomic operations to create files and folders, etc. It also has a KnownFolders class with static references to different library folders like documents, videos, photos, plus RemovableDevices. Additionally does ApplicationData.Current provide references to the app's temporary, local and roaming folder.
Unfortunately there's no built-in way to check for the available free storage size / free disk space at those locations, although there are scenarios where that information can be essential, especially when dealing with removable devices. But no worries, the good old Win32 has it covered with the GetFreeDiskSpaceEx  function and it can be used with Windows 8 and Windows Phone 8. In order to use it from managed code it just has to be called through P/Invoke or wrapped in a WinRT component which I prefer nowadays, therefore this post provides a short WinRT C++/Cx snippet.

I assume you know how to create a custom C++/Cx WinRT component with Visual Studio, if not go back to my previous blog post which shows just that.

How it works

  1. Open the generated precompiled header file pch.h of your WinRT component's Visual Studio project and add an include for windows.h:
    // pch.h - Header for standard system include files.
    #pragma once
    #include <windows.h>

  2. Open the header file of your component and add the method declaration of GetAvailableBytes to your WinRT component which will internally use the GetFreeDiskSpaceEx, but only takes a path as string parameter and returns a WinRT uint64 (unsigned long) type with the available free space in bytes.
    namespace MyNativeStuff
        public ref class MyStorageExtensions sealed
            uint64 GetAvailableBytes(Platform::String^ path);

  3. Add the method implementation in the source file of the component (.cpp).
    The GetDiskFreeSpaceEx function takes a pointer to an ULARGE_INTEGER which is an union from ancient times when compilers didn't support 64 bit types. Our method then returns the filled unsigned long QuadPart of it.
    #include "pch.h"
    #include "MyNativeStuff.h"
    using namespace MyNativeStuff;
    using namespace Platform;
    uint64 MyStorageExtensions::GetAvailableBytes(Platform::String^ path)
        ULARGE_INTEGER availableBytesToCaller;
        availableBytesToCaller.QuadPart = 0;
        GetDiskFreeSpaceEx(path->Data(), &availableBytesToCaller, NULL, NULL);
        return availableBytesToCaller.QuadPart;

  4. You are now ready to use the component in your managed C# code.
    var myNativeComponent = new MyNativeStuff.MyStorageExtensions();
    // Create a folder in temp folder of the app and check the available free space
    var myTempFolder = await ApplicationData.Current.TemporaryFolder.CreateFolderAsync("test", CreationCollisionOption.OpenIfExists);
    var availableSpaceTempFolder = myNativeComponent.GetAvailableBytes(myTempFolder.Path);
    // Create a folder in videos lib and check the available free space
    var myVideoFolder = await KnownFolders.VideosLibrary.CreateFolderAsync("test", 
    var availableSpaceVideoLib = myNativeComponent.GetAvailableBytes(myVideoFolder.Path);

Note, the GetFreeDiskSpaceEx works with any directory path the calling code is allowed to access.

Tuesday, January 7, 2014

Windows Phone Natives - How to Leverage Native Code on Windows Phone

With Windows Phone 8 the possibility to use native code for development was introduced to the public SDK. It's a powerful feature and it can help to improve the performance for certain heavy computing tasks, reduce the memory footprint or just to leverage certain APIs which are only available in native code. Media Foundation or Direct3D for example are native only, but it could as well be a proprietary library from another third party written in C/C++.
In order to use native code on Windows Phone one has to write a native Windows Phone Runtime Component (WinPRT). Such a WinPRT library encapsulates the native code internally and only exposes WinRT types, therefore it can be consumed through the WinMD projections also in managed C# projects.

This blog post provides an introduction with an easy sample to get started. The MSDN also provides a very good Windows Phone native code overview, a list of the available Win32 and COM APIs on Windows Phone including an index of all supported Win32 functions. It contains such important things like the native sockets API Winsock, the National Language Support (NLS) functions for all things around region, language and culture and much more native APIs.

How it works

  1. First of all you need to create a Windows Phone App 8 project with Visual Studio.

  2. Then add a new Visual C++ Windows Phone Runtime Component (WinPRT) project to the solution.

  3. Now you need to add the solution's WinPRT project as reference to the App project. Note that Visual Studio will automatically take care of adding the required ActivatableClass definition to your consuming App project. Refer to this if you ever need to add a WinRT component manually to another project.

  4. Open the generated precompiled header file pch.h and add an include for windows.h:
    // pch.h - Header for standard system include files.
    #pragma once
    #include <windows.h>

    For this sample we use the Win32 function IsProcessorFeaturePresent to query if certain processor features are supported. This function is defined in windows.h.

  5. Open the header file of your component (ProcessorInfoComponent.h) and add the method declaration of IsNeonSupported to our WinPRT component which will internally use the IsProcessorFeaturePresent, but only expose a WinRT bool type. The MSDN has a nice Quick Reference which provides a table how Standard C++ types and constructs map to C++/Cx WinRT.
    namespace ProcessorInfoComponent
        public ref class ProcessorInfoProvider sealed
           bool IsNeonSupported();

  6. Open the source file (ProcessorInfoComponent.cpp) and add the method implementation to our WinPRT component which will call IsProcessorFeaturePresent and return the result.
    The IsNeonSupported wrapper method here will provide the information if the processor supports the ARM VFP/Neon: 32 x 64bit register bank. There are many other queryable parameters available beside PF_ARM_VFP_32_REGISTERS_AVAILABLE used here. Those are defined in winnt.h and partly documented at the MSDN.
    #include "ProcessorInfoComponent.h"
    using namespace ProcessorInfoComponent;
    bool ProcessorInfoProvider::IsNeonSupported()
       return IsProcessorFeaturePresent(PF_ARM_VFP_32_REGISTERS_AVAILABLE);

  7. You are now ready to use the component in your managed C# code.
    private void Button_Click(object sender, RoutedEventArgs e)
       var infoProvider = new ProcessorInfoComponent.ProcessorInfoProvider();
       var hasNeon = infoProvider.IsNeonSupported();
       Info.Text = string.Format("Is ARM Neon supported: {0}", hasNeon);
The complete sample solution can be downloaded here.
If you run the sample in the emulator you will see IsNeonSupported() returns false, since it's running on the x86 CPU, but if you execute the sample on a device IsNeonSupported() should return true. Keep in mind you are now using native code so you have to compile a build for ARM (device) or x86 (emulator). AnyCPU won't work anymore.

The presented is just a very easy sample but it already shows how native code on Windows Phone can help you to access information not available otherwise.