Load image from KnownFolders into BitmapImage - cocos2d-iphone

Question

auto task = create_task(Windows::Storage::KnownFolders::PicturesLibrary->GetFilesAsync(Windows::Storage::Search::CommonFileQuery::OrderBySearchRank));
task.then([&sstrpath](Windows::Foundation::Collections::IVectorView<Windows::Storage::StorageFile^>^ files)
{
CCLog("num of files detected %d",files->Size);
Platform::String^ pathstr = files->GetAt(0)->Path;
OutputDebugStringW(pathstr->Data());
auto task2 = create_task(files->GetAt(0)->OpenAsync(Windows::Storage::FileAccessMode::Read));
task2.then([](Windows::Storage::Streams::IRandomAccessStream^ filestream)
{
Windows::UI::Xaml::Media::Imaging::BitmapImage^ bmp = ref new Windows::UI::Xaml::Media::Imaging::BitmapImage();
bmp->SetSource(filestream);
}
);
}
);
This was done on a Win8 RTM with a VS express RTM in C++ (cocos2dx framework). I am trying to load an image from the Picture library and create a BitmapImage out of it. Next was to somehow use the BitmapImage for CCSprite in cococs2dx, but that's not the issue here. The program was able to run all the way into task2 but then crash at when I try to ref new the BitmmapImage. The following was in the output console
First-chance exception at 0x75004B32 in myGame.exe: Microsoft C++ exception:
Platform::WrongThreadException ^ at memory location 0x02D1D794. HRESULT:0x8001010E
First-chance exception at 0x75004B32 in myGame.exe: Microsoft C++ exception: [rethrow] at memory location 0x00000000.
First-chance exception at 0x75004B32 in myGame.exe: Microsoft C++ exception:
Platform::WrongThreadException ^ at memory location 0x02D1E5F0. HRESULT:0x8001010E
Unhandled exception at 0x622C9AD1 (msvcr110d.dll) in PixBlitz.exe: An invalid parameter was passed to a function that considers invalid parameters fatal.
I am not really sure what I have done wrong as most tutorials out there are Javascript or XAML based for Win8 app development.

Answer 1

Creating tasks like that moves code onto different threads. You're getting Platform::WrongThreadException when you access an object from the wrong thread. You have to access GUI components from the same thread every time.
I believe if you RunAsync onto the Dispatcher, that will get the threading right. Pass a delegate to RunAsync, and have that delegate include creating the BitmapImage, and whatever else you want to do with the BitmapImage.
As requested, an example.
I'm not familiar with Win8 development, though I am familiar with the WPF that it's based on. (If C++/CLI supports lambdas now, I'll have to go back and revise some old answers on the subject.)
I believe this is what you want. I may have some of the syntax slightly off on that delegate.
Stream^ filesteam = files->GetAt(0)->Open(FileAccessMode::Read); // we're already on a background thread, no need for a Task if we're not going to call 'then'.
// I'm assuming 'this' is a subclass of Windows.UI.Xaml.Window, or something similar.
this->Dispatcher->RunAsync(CoreDispatcherPriority::Low, []()
{
BitmapImage^ bmp = ref new BitmapImage();
bmp->SetSource(filestream);
}
);