UWP 后退按钮和事件处理程序 - C++

Question

我是 Windows 10 个 UWP 应用程序的新手，目前我正在尝试应用程序中的各种导航技术。我在 UWP 应用程序中搜索了后退按钮功能，但似乎无法理解我必须将 "provided code" 放在哪里以及如何执行它。我也尝试过自己做，但它在 Visual Studio 中抛出各种关于未找到标识符的错误。

第一个代码是：

    Windows::UI::Core::SystemNavigationManager::GetForCurrentView()->
    BackRequested += ref new Windows::Foundation::EventHandler<
    Windows::UI::Core::BackRequestedEventArgs^>(
    this, &App::App_BackRequested);

第二段代码为：

    void App::App_BackRequested(
    Platform::Object^ sender, 
    Windows::UI::Core::BackRequestedEventArgs^ e)
    {
    Frame^ rootFrame = dynamic_cast<Frame^>(Window::Current->Content);
    if (rootFrame == nullptr)
    return;

    // Navigate back if possible, and if the event has not
    // already been handled.
    if (rootFrame->CanGoBack && e->Handled == false)
        {
            e->Handled = true;
            rootFrame->GoBack();
        }
    }

请帮助我解决这个问题并告诉我如何在我的 UWP 应用程序中实现此代码。谢谢

来源：https://msdn.microsoft.com/en-us/library/windows/apps/mt465734.aspx

Answer 1

我设法以某种方式把它弄对了，第一个代码放在 "OnLaunched" 事件下的 App.xaml 代码隐藏文件中。第二个代码放在上面文件的最后，它的前向声明放在头文件中。

Answer 2

应该如下所示：

这是 App.xaml.cpp 中的 OnLaunched 方法 class:

在结束之前，您应该粘贴第一个片段：

 void App::OnLaunched(Windows::ApplicationModel::Activation::LaunchActivatedEventArgs^ e)
{
#if _DEBUG
// Show graphics profiling information while debugging.
if (IsDebuggerPresent())
{
    // Display the current frame rate counters
     DebugSettings->EnableFrameRateCounter = true;
}
#endif
auto rootFrame = dynamic_cast<Frame^>(Window::Current->Content);

// Do not repeat app initialization when the Window already has content,
// just ensure that the window is active
if (rootFrame == nullptr)
{
    // Create a Frame to act as the navigation context and associate it with
    // a SuspensionManager key
    rootFrame = ref new Frame();

    rootFrame->NavigationFailed += ref new Windows::UI::Xaml::Navigation::NavigationFailedEventHandler(this, &App::OnNavigationFailed);

    if (e->PreviousExecutionState == ApplicationExecutionState::Terminated)
    {
        // TODO: Restore the saved session state only when appropriate, scheduling the
        // final launch steps after the restore is complete

    }


    if (e->PrelaunchActivated == false)
    {
        if (rootFrame->Content == nullptr)
        {
            // When the navigation stack isn't restored navigate to the first page,
            // configuring the new page by passing required information as a navigation
            // parameter
            rootFrame->Navigate(TypeName(MainPage::typeid), e->Arguments);
        }
        // Place the frame in the current Window
        Window::Current->Content = rootFrame;
        // Ensure the current window is active
        Window::Current->Activate();
    }
}
else
{
    if (e->PrelaunchActivated == false)
    {
        if (rootFrame->Content == nullptr)
        {
            // When the navigation stack isn't restored navigate to the first page,
            // configuring the new page by passing required information as a navigation
            // parameter
            rootFrame->Navigate(TypeName(MainPage::typeid), e->Arguments);
        }
        // Ensure the current window is active
        Window::Current->Activate();
    }
}

Windows::UI::Core::SystemNavigationManager::GetForCurrentView()->
    BackRequested += ref new Windows::Foundation::EventHandler<
    Windows::UI::Core::BackRequestedEventArgs^>(
        this, &App::App_BackRequested);
 }

现在请在 OnLaunched 方法下粘贴此处理程序：

void App::App_BackRequested(
Platform::Object^ sender,
Windows::UI::Core::BackRequestedEventArgs^ e)
{
Frame^ rootFrame = dynamic_cast<Frame^>(Window::Current->Content);
if (rootFrame == nullptr)
    return;

// Navigate back if possible, and if the event has not
// already been handled.
if (rootFrame->CanGoBack && e->Handled == false)
  {
    e->Handled = true;
    rootFrame->GoBack();
  }
}

您还需要将以下代码添加到 App.xaml.h:

ref class 应用密封（Visual Studio 可以自动添加）： { 受保护： virtual void OnLaunched(Windows::ApplicationModel::Activation::LaunchActivatedEventArgs^ e) override;

    void App_BackRequested(Platform::Object ^ sender, Windows::UI::Core::BackRequestedEventArgs ^ e);

internal:
    App();

private:
    void OnSuspending(Platform::Object^ sender, Windows::ApplicationModel::SuspendingEventArgs^ e);
    void OnNavigationFailed(Platform::Object ^sender, Windows::UI::Xaml::Navigation::NavigationFailedEventArgs ^e);
};

希望对您有所帮助。

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