Windows Phone: Handle back-button press

When the back button is pressed, send an immediate key event to the
topmost window (or the application if there is no window). If it is
accepted, mark the native event as accepted and send a key release event.
This way, the application may call accept() on the KeyPress event for
Qt::Key_Back in order to create backstepping behaviors within the app.

This is in line with Android, which quits the app when the event is
ignored. On Windows Phone, the default behavior occurs when the event is
ignored, which is to back out of the application and leave it running
in the background.

Task-number: QTBUG-35951
Change-Id: I46d15478f441f73d3660370370689b2f9fa11f25
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>

2 files changed, 50 insertions, 0 deletions

diff --git a/src/plugins/platforms/winrt/qwinrtscreen.cpp b/src/plugins/platforms/winrt/qwinrtscreen.cpp
index d3ede89865..2e38f81499 100644
--- a/src/plugins/platforms/winrt/qwinrtscreen.cpp
+++ b/src/plugins/platforms/winrt/qwinrtscreen.cpp
@@ -63,6 +63,9 @@
 #include <windows.ui.viewmanagement.h>
 #include <windows.graphics.display.h>
 #include <windows.foundation.h>
+#ifdef Q_OS_WINPHONE
+#include <windows.phone.ui.input.h>
+#endif
 
 using namespace Microsoft::WRL;
 using namespace Microsoft::WRL::Wrappers;
@@ -75,6 +78,9 @@ using namespace ABI::Windows::UI::Input;
 using namespace ABI::Windows::UI::ViewManagement;
 using namespace ABI::Windows::Devices::Input;
 using namespace ABI::Windows::Graphics::Display;
+#ifdef Q_OS_WINPHONE
+using namespace ABI::Windows::Phone::UI::Input;
+#endif
 
 typedef IEventHandler<IInspectable*> ResumeHandler;
 typedef IEventHandler<SuspendingEventArgs*> SuspendHandler;
@@ -87,6 +93,9 @@ typedef ITypedEventHandler<CoreWindow*, PointerEventArgs*> PointerHandler;
 typedef ITypedEventHandler<CoreWindow*, WindowSizeChangedEventArgs*> SizeChangedHandler;
 typedef ITypedEventHandler<CoreWindow*, VisibilityChangedEventArgs*> VisibilityChangedHandler;
 typedef ITypedEventHandler<CoreWindow*, AutomationProviderRequestedEventArgs*> AutomationProviderRequestedHandler;
+#ifdef Q_OS_WINPHONE
+typedef IEventHandler<BackPressedEventArgs*> BackPressedHandler;
+#endif
 
 QT_BEGIN_NAMESPACE
 
@@ -465,6 +474,11 @@ QWinRTScreen::QWinRTScreen(ICoreWindow *window)
     m_coreWindow->add_PointerReleased(Callback<PointerHandler>(this, &QWinRTScreen::onPointerUpdated).Get(), &m_tokens[QEvent::MouseButtonRelease]);
     m_coreWindow->add_PointerWheelChanged(Callback<PointerHandler>(this, &QWinRTScreen::onPointerUpdated).Get(), &m_tokens[QEvent::Wheel]);
     m_coreWindow->add_SizeChanged(Callback<SizeChangedHandler>(this, &QWinRTScreen::onSizeChanged).Get(), &m_tokens[QEvent::Resize]);
+#ifdef Q_OS_WINPHONE
+    ComPtr<IHardwareButtonsStatics> hardwareButtons;
+    if (SUCCEEDED(GetActivationFactory(HString::MakeReference(RuntimeClass_Windows_Phone_UI_Input_HardwareButtons).Get(), &hardwareButtons)))
+        hardwareButtons->add_BackPressed(Callback<BackPressedHandler>(this, &QWinRTScreen::onBackButtonPressed).Get(), &m_tokens[QEvent::User]);
+#endif // Q_OS_WINPHONE
 
     // Window event handlers
     m_coreWindow->add_Activated(Callback<ActivatedHandler>(this, &QWinRTScreen::onActivated).Get(), &m_tokens[QEvent::WindowActivate]);
@@ -1002,4 +1016,27 @@ HRESULT QWinRTScreen::onOrientationChanged(IInspectable *)
     return S_OK;
 }
 
+#ifdef Q_OS_WINPHONE
+HRESULT QWinRTScreen::onBackButtonPressed(IInspectable *, IBackPressedEventArgs *args)
+{
+    QKeyEvent backPress(QEvent::KeyPress, Qt::Key_Back, Qt::NoModifier);
+    backPress.setAccepted(false);
+
+    QObject *receiver = m_visibleWindows.isEmpty()
+            ? static_cast<QObject *>(QGuiApplication::instance())
+            : static_cast<QObject *>(m_visibleWindows.first());
+
+    // If the event is ignored, the app will suspend
+    QGuiApplication::sendEvent(receiver, &backPress);
+    if (backPress.isAccepted()) {
+        args->put_Handled(true);
+        // If the app accepts the event, send the release for symmetry
+        QKeyEvent backRelease(QEvent::KeyRelease, Qt::Key_Back, Qt::NoModifier);
+        QGuiApplication::sendEvent(receiver, &backRelease);
+    }
+
+    return S_OK;
+}
+#endif // Q_OS_WINPHONE
+
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/winrt/qwinrtscreen.h b/src/plugins/platforms/winrt/qwinrtscreen.h
index 3131f879b5..c6511e9446 100644
--- a/src/plugins/platforms/winrt/qwinrtscreen.h
+++ b/src/plugins/platforms/winrt/qwinrtscreen.h
@@ -80,6 +80,15 @@ namespace ABI {
                 struct IDisplayPropertiesStatics;
             }
         }
+#ifdef Q_OS_WINPHONE
+        namespace Phone {
+            namespace UI {
+                namespace Input {
+                    struct IBackPressedEventArgs;
+                }
+            }
+        }
+#endif
     }
 }
 struct IInspectable;
@@ -149,6 +158,10 @@ private:
 
     HRESULT onOrientationChanged(IInspectable *);
 
+#ifdef Q_OS_WINPHONE
+    HRESULT onBackButtonPressed(IInspectable *, ABI::Windows::Phone::UI::Input::IBackPressedEventArgs *args);
+#endif
+
     ABI::Windows::UI::Core::ICoreWindow *m_coreWindow;
     ABI::Windows::UI::ViewManagement::IApplicationViewStatics *m_applicationView;
     ABI::Windows::ApplicationModel::Core::ICoreApplication *m_application;