iOS: Disable three-finger-tap editing interaction menu when there's no focus object

A typical Qt application, such as a QML application, is a single full
screen QUIView, containing all of the granular controls of the UI.

The view accepts first responder status, so that we can pass on text
input to a possible text field inside the UI. That however triggers iOS
to bring up the editing interaction menu whenever the user taps with
three fingers, as iOS can't know that only parts of our view is suitable
for interaction.

To mitigate that we override the editingInteractionConfiguration getter
of the view, as documented, and dynamically report the correct enablement
based on whether we have an active focus object that accepts input.

This works because iOS queries the getter from the three finger tap
gesture recognizer, before showing the menu.

Change-Id: I0874340c42e437e1d7251896993f2eafe122f09e
Fixes: QTBUG-89735
Pick-to: 6.0 6.1 5.15
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/plugins/platforms/ios/quiview.mm

@@ -45,6 +45,7 @@
 #include "qiostextresponder.h"
 #include "qiosscreen.h"
 #include "qioswindow.h"
+#include "qiosinputcontext.h"
 #ifndef Q_OS_TVOS
 #include "qiosmenu.h"
 #endif
@@ -682,6 +683,18 @@ Q_LOGGING_CATEGORY(lcQpaTablet, "qt.qpa.input.tablet")
     [super addInteraction:interaction];
 }
 
+- (UIEditingInteractionConfiguration)editingInteractionConfiguration
+{
+    // We only want the three-finger-tap edit menu to be available when there's
+    // actually something to edit. Otherwise the OS will cause a slight delay
+    // before delivering the release of three finger touch input. Note that we
+    // do not do any hit testing here to check that the focus object is the one
+    // being tapped, as the behavior of native iOS apps is to trigger the menu
+    // regardless of where the gesture is being made.
+    return QIOSInputContext::instance()->inputMethodAccepted() ?
+        UIEditingInteractionConfigurationDefault : UIEditingInteractionConfigurationNone;
+}
+
 @end
 
 @implementation UIView (QtHelpers)