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, 25 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickwindow/data/windowattached.qml b/tests/auto/quick/qquickwindow/data/windowattached.qml
new file mode 100644
index 0000000000..e000d5c6fd
--- /dev/null
+++ b/tests/auto/quick/qquickwindow/data/windowattached.qml
@@ -0,0 +1,25 @@
+import QtQuick 2.4
+import QtQuick.Window 2.2
+
+Rectangle {
+    id: root
+    width: 100
+    height: 100
+    property bool windowActive: root.Window.active
+    Text {
+        objectName: "rectangleWindowText"
+        anchors.centerIn: parent
+        text: (windowActive ? "active" : "inactive") + "\nvisibility: " + root.Window.visibility
+    }
+
+    property Window extraWindow: Window {
+        objectName: "extraWindow"
+        title: "extra window"
+        visible: true
+        Text {
+            objectName: "extraWindowText"
+            anchors.centerIn: parent
+            text: (extraWindow.active ? "active" : "inactive") + "\nvisibility: " + Window.visibility
+        }
+    }
+}