WinRT/C++使用UIViewSettings检测平板模式时GetForCurrentView报错

我们有一个纯Win32/C++应用，需要检测Windows 10的平板模式。现有一段可用的WRL代码，通过访问Windows.UI.ViewManagement.UIViewSettings.UserInteractionMode属性实现检测：

WRL::ComPtr<IUIViewSettingsInterop> interop;
if (SUCCEEDED(Windows::Foundation::GetActivationFactory(WRL::Wrappers::HStringReference(
    RuntimeClass_Windows_UI_ViewManagement_UIViewSettings).Get(),
    &interop)) && interop)
{
    WRL::ComPtr<vm::IUIViewSettings> pViewSettings;
    if (SUCCEEDED(interop->GetForWindow(hWnd, IID_PPV_ARGS(&pViewSettings))) && pViewSettings)
    {
        vm::UserInteractionMode currentMode;
        if (SUCCEEDED(pViewSettings->get_UserInteractionMode(&currentMode)))
            return currentMode == vm::UserInteractionMode::UserInteractionMode_Touch;
    }
}

但我们希望改用WinRT实现，尝试了以下代码，虽然编译正常，但调用GetForCurrentView()时会抛出HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND)异常：

auto uiSettings = winrt::Windows::UI::ViewManagement::UIViewSettings::GetForCurrentView();
return uiSettings.UserInteractionMode() == winrt::Windows::UI::ViewManagement::UserInteractionMode::Touch;

问题根源在于，纯Win32应用没有自动关联WinRT的视图上下文，GetForCurrentView()找不到对应的视图，必须像WRL代码那样显式传入窗口句柄来绑定。

解决方案 #

在WinRT中，我们需要借助interop接口来实现窗口句柄到UIViewSettings对象的绑定，具体步骤如下：

1. 获取IUIViewSettingsInterop接口的激活工厂
2. 调用其GetForWindow方法，传入Win32窗口句柄，获取对应的UIViewSettings实例
3. 读取UserInteractionMode属性判断是否处于平板模式

完整WinRT代码示例 #

#include <winrt/Windows.UI.ViewManagement.h>
#include <windows.ui.viewmanagement.interop.h>

bool IsTabletMode(HWND hWnd)
{
    // 获取IUIViewSettingsInterop接口
    winrt::com_ptr<IUIViewSettingsInterop> uiViewSettingsInterop;
    winrt::check_hresult(
        ::Windows::Foundation::GetActivationFactory(
            winrt::hstring{L"Windows.UI.ViewManagement.UIViewSettings"},
            uiViewSettingsInterop.put()
        )
    );

    // 通过窗口句柄获取UIViewSettings对象
    winrt::Windows::UI::ViewManagement::UIViewSettings uiSettings;
    winrt::check_hresult(
        uiViewSettingsInterop->GetForWindow(
            hWnd,
            winrt::guid_of<winrt::Windows::UI::ViewManagement::IUIViewSettings>(),
            winrt::put_abi(uiSettings)
        )
    );

    // 判断是否为触摸交互模式（平板模式）
    return uiSettings.UserInteractionMode() == winrt::Windows::UI::ViewManagement::UserInteractionMode::Touch;
}

代码说明 #

• 使用winrt::com_ptr作为WinRT原生智能指针，替代WRL的ComPtr
• winrt::check_hresult会自动将失败的HRESULT转换为异常，也可以根据需求改为手动检查返回值
• winrt::guid_of用于获取WinRT接口的GUID，替代WRL中的IID_PPV_ARGS
• winrt::put_abi用来获取WinRT对象的底层COM指针地址，供interop方法调用

内容的提问来源于stack exchange，提问作者Jonathan Potter