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, 110 insertions, 0 deletions

diff --git a/src/quick/items/qquickwindowattached.cpp b/src/quick/items/qquickwindowattached.cpp
new file mode 100644
index 0000000000..666b21f6cd
--- /dev/null
+++ b/src/quick/items/qquickwindowattached.cpp
@@ -0,0 +1,110 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtQuick module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qquickwindow.h"
+#include "qquickitem.h"
+#include "qquickwindowattached_p.h"
+
+QT_BEGIN_NAMESPACE
+
+// QDoc comments must go in qquickwindow.cpp to avoid overwriting the Window docs
+
+QQuickWindowAttached::QQuickWindowAttached(QObject* attachee)
+    : QObject(attachee)
+    , m_window(NULL)
+{
+    m_attachee = qobject_cast<QQuickItem*>(attachee);
+    if (m_attachee && m_attachee->window()) // It might not be in a window yet
+        windowChanged(m_attachee->window());
+    if (m_attachee)
+        connect(m_attachee, &QQuickItem::windowChanged, this, &QQuickWindowAttached::windowChanged);
+}
+
+QWindow::Visibility QQuickWindowAttached::visibility() const
+{
+    return (m_window ? m_window->visibility() : QWindow::Hidden);
+}
+
+bool QQuickWindowAttached::isActive() const
+{
+    return (m_window ? m_window->isActive() : false);
+}
+
+QQuickItem *QQuickWindowAttached::activeFocusItem() const
+{
+    return (m_window ? m_window->activeFocusItem() : Q_NULLPTR);
+}
+
+void QQuickWindowAttached::windowChanged(QQuickWindow *window)
+{
+    if (window != m_window) {
+        QQuickWindow* oldWindow = m_window;
+        m_window = window;
+
+        if (oldWindow)
+            oldWindow->disconnect(this);
+
+        if (!window)
+            return; // No values to get, therefore nothing to emit
+
+        if (!oldWindow || window->visibility() != oldWindow->visibility())
+            emit visibilityChanged();
+        if (!oldWindow || window->isActive() != oldWindow->isActive())
+            emit activeChanged();
+        if (!oldWindow || window->activeFocusItem() != oldWindow->activeFocusItem())
+            emit activeFocusItemChanged();
+
+        // QQuickWindowQmlImpl::visibilityChanged also exists, and window might even
+        // be QQuickWindowQmlImpl, but that's not what we are connecting to.
+        // So this is actual window state rather than a buffered or as-requested one.
+        // If we used the metaobject connect syntax there would be a warning:
+        // QMetaObjectPrivate::indexOfSignalRelative - QMetaObject::indexOfSignal:
+        // signal visibilityChanged(QWindow::Visibility) from QQuickWindow redefined in QQuickWindowQmlImpl
+        connect(window, &QQuickWindow::visibilityChanged,
+                this, &QQuickWindowAttached::visibilityChanged);
+        connect(window, &QQuickWindow::activeChanged,
+                this, &QQuickWindowAttached::activeChanged);
+        connect(window, &QQuickWindow::activeFocusItemChanged,
+                this, &QQuickWindowAttached::activeFocusItemChanged);
+    }
+}
+
+QT_END_NAMESPACE