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);
    }
    );
}
);

这是在Win8 RTM上用C ++中的VS express RTM（cocos2dx框架）完成的。我正在尝试从图片库加载图像并从中创建一个BitmapImage。接下来是以某种方式在cococs2dx中使用Cmapprite的BitmapImage，但这不是问题。该程序能够一直运行到task2，但在我尝试引入BitmmapImage时崩溃。以下是在输出控制台

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.

我不确定我做错了什么，因为大多数教程都是基于Win8应用程序开发的Javascript或XAML。

Answer 1

创建类似的任务将代码移动到不同的线程上。当您从错误的线程访问对象时，您将获得Platform :: WrongThreadException。您必须每次都从同一个线程访问GUI组件。

我相信如果您将RunAsync运行到Dispatcher，那么线程就会正确。将委托传递给RunAsync，并让该委托包括创建BitmapImage，以及您想要对BitmapImage做什么。

根据要求，举个例子。

我不熟悉Win8开发，虽然我熟悉它所基于的WPF。（如果C ++ / CLI现在支持lambdas，我将不得不回过头来修改一些关于这个主题的旧答案。）

我相信这就是你想要的。我可能会在该委托上稍微关闭一些语法。

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);
}
);

将图像从KnownFolders加载到BitmapImage中

1 个答案: