Add Window attached property on Item

An Item sometimes needs to know a few things about the window
in which it is being displayed; this attached property can expose
them without needing to go up the heirarchy to find the window.
Instead of adding the QQuickWindow pointer as a property on Item
as in 8f49f50a169db85401eb37daf4fe3a0fc3280603, having an attached
property means that it will not be found by introspection; and
it solves the problem that Window is in the QtQuick.Window module:
you must import the module to use the attached property, instead
of having access to a pointer whose type might not be defined
if you didn't import it.  The Window attached property is created
on-demand (so the memory cost adds up if you use it in too many
places); the tradeoff is that it can exist even when the item
is not yet being shown in a window, so bindings at startup work.
The API is purposely incomplete compared to that in QQuickWindow
so that we can introduce what is needed in a controlled fasion
over time.  For now we know of use cases for visibility, active
and activeFocusItem.

[ChangeLog][QtQuick][Window] Added Item.Window attached property

Change-Id: I649404cbd1383326678aa2144f790b2f2542dbbc
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/quick/items/qquickwindow.h b/src/quick/items/qquickwindow.h
index 6353f6a30c..04a89b1d3d 100644
--- a/src/quick/items/qquickwindow.h
+++ b/src/quick/items/qquickwindow.h
@@ -47,6 +47,7 @@
 #include <QtGui/qopengl.h>
 #include <QtGui/qwindow.h>
 #include <QtGui/qevent.h>
+#include <qqml.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -55,6 +56,7 @@ class QQuickItem;
 class QSGTexture;
 class QInputMethodEvent;
 class QQuickWindowPrivate;
+class QQuickWindowAttached;
 class QOpenGLFramebufferObject;
 class QQmlIncubationController;
 class QInputMethodEvent;
@@ -156,6 +158,8 @@ public:
 
     void scheduleRenderJob(QRunnable *job, RenderStage schedule);
 
+    static QQuickWindowAttached *qmlAttachedProperties(QObject *object);
+
 Q_SIGNALS:
     void frameSwapped();
     Q_REVISION(2) void openglContextCreated(QOpenGLContext *context);
@@ -220,6 +224,7 @@ private:
 QT_END_NAMESPACE
 
 Q_DECLARE_METATYPE(QQuickWindow *)
+QML_DECLARE_TYPEINFO(QQuickWindow, QML_HAS_ATTACHED_PROPERTIES)
 
 #endif // QQUICKWINDOW_H