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/qquickwindowmodule.cpp b/src/quick/items/qquickwindowmodule.cpp
index 51053ea801..f472d5b867 100644
--- a/src/quick/items/qquickwindowmodule.cpp
+++ b/src/quick/items/qquickwindowmodule.cpp
@@ -40,6 +40,7 @@
 ****************************************************************************/
 
 #include "qquickwindowmodule_p.h"
+#include "qquickwindowattached_p.h"
 #include "qquickscreen_p.h"
 #include "qquickview_p.h"
 #include <QtQuick/QQuickWindow>
@@ -173,6 +174,10 @@ void QQuickWindowModule::defineModule()
 {
     const char uri[] = "QtQuick.Window";
 
+    // Since Window is both an attached property and a createable type,
+    // the attached property declaration must come first so that it can
+    // be overridden below.
+    qmlRegisterUncreatableType<QQuickWindow>(uri, 2, 2, "Window", QQuickWindow::tr("Window is available via attached properties"));
     qmlRegisterType<QQuickWindow>(uri, 2, 0, "Window");
     qmlRegisterRevision<QWindow,1>(uri, 2, 1);
     qmlRegisterRevision<QWindow,2>(uri, 2, 2);