从 c++/cx 中的回调内部调用 UI 线程上的问题

Question

这是我的回调函数：

void VideoCapturerSampleCallback(struct LmiVideoCapturer_* capturer, const LmiVideoFrame* videoFrame, LmiVoidPtr userData)
{
  //TODO will have to be on ui thread;
  Windows::ApplicationModel::Core::CoreApplication::MainView->CoreWindow->Dispatcher->RunAsync(0, ref new Windows::UI::Core::DispatchedHandler([this]()
{
    Windows::UI::Xaml::Media::Imaging::BitmapImage^ bitmapImage =
        ref new Windows::UI::Xaml::Media::Imaging::BitmapImage();
    auto uri = ref new Windows::Foundation::Uri("ms-appx:///Assets/1.jpg");
    if (first){
        first = false;
    }
    else{
        uri = ref new Windows::Foundation::Uri("ms-appx:///Assets/1.jpg");
        first = true;
    }
    bitmapImage->UriSource = uri;
    media->Source = bitmapImage;
}));
}

基本上每次调用回调都会换图片，目前我只是从Assets换了2张图片，看看能不能用。这是我在日志中得到的错误：

Error   17  error C1903: unable to recover from previous error(s); stopping compilation C:\Users\Alin Rosu\Downloads\App2\App2\MainPage.xaml.cpp    109 1   App2
Error   16  error C3482: 'this' can only be used as a lambda capture within a non-static member function    C:\Users\Alin Rosu\Downloads\App2\App2\MainPage.xaml.cpp    93  1   App2
19  IntelliSense: 'this' may only be used inside a nonstatic member function    c:\Users\Alin Rosu\Downloads\App2\App2\MainPage.xaml.cpp    93  144 App2
18  IntelliSense: function "Windows::UI::Core::CoreDispatcher::RunAsync" cannot be called with the given argument list
        argument types are: (int, Windows::UI::Core::DispatchedHandler ^)
        object type is: Windows::UI::Core::CoreDispatcher ^ c:\Users\Alin Rosu\Downloads\App2\App2\MainPage.xaml.cpp    93  84  App2

现在是否可以在回调中使用 [this] 而不会出错？我是一名 Android 开发人员，所以对我来说，对此的逻辑响应是创建一个全局变量 App2::MainPage，然后在构造函数中，将 "this" 保存在其中，这样我就可以那里的上下文，并尝试用它调用 RunAsync，但它不起作用。是否可以通过其他方式实例化 DispatchedHandler？

Answer 1

这样声明上下文：

App2::MainPage^ context;

然后在MainPage函数中设置：

MainPage::MainPage()
{
InitializeComponent();
media = this->player;
context = this;
}

然后我在 VideoCapturerSampleCallback 中这样做：

void VideoCapturerSampleCallback(struct LmiVideoCapturer_* capturer, const LmiVideoFrame* videoFrame, LmiVoidPtr userData)
{
App2::MainPage^ ctx = context;
Windows::ApplicationModel::Core::CoreApplication::MainView->CoreWindow->Dispatcher->RunAsync(Windows::UI::Core::CoreDispatcherPriority::Normal, ref new Windows::UI::Core::DispatchedHandler([ctx]()
{
    //TODO will need to set in here
    Windows::UI::Xaml::Media::Imaging::BitmapImage^ bitmapImage =
        ref new Windows::UI::Xaml::Media::Imaging::BitmapImage();
    auto uri = ref new Windows::Foundation::Uri("ms-appx:///Assets/1.jpg");
    if (first){
        XTRACE(L"===================FIIIIIIIIIIIIRST =======================\n");
        first = false;
    }
    else{
        XTRACE(L"===================FIIIIIIIIIIIIRST FAAAALSEEEEE=======================\n");
        uri = ref new Windows::Foundation::Uri("ms-appx:///Assets/2.jpg");
        first = true;
    }
    bitmapImage->UriSource = uri;
    media->Source = bitmapImage;
}));
}

这解决了我的问题，我可以修改 UI，在 UI 线程上。

从 c++/cx 中的回调内部调用 UI 线程上的问题

Issue calling something on the UI Thread from inside a callback in c++/cx

visual-studio

asynchronous

dispatcher

c++-cx

ui-thread