Add anchors property to Popup to allow centering in parent/window

Currently, users must manually position their Popup using x and y
bindings:

    Popup {
        x: (parent.width - width) / 2
        y: (parent.height - height) / 2
    }

This patch adds an anchors property so that you can do this instead:

    Popup {
        anchors.centerIn: parent
    }

It's also possible to conveniently center within the window from
anywhere within the scene (106e7b63 also documents an alternative way
of doing this using Overlay):

    Window {
        id: window

        Pane {
            Popup {
                anchors.centerIn: window
            }
        }
    }

QQuickAnchors were never used with Popup, because we cannot use the
QQuickAnchors implementation as-is, as the visual QQuickItem parent
is not the actual parent item of QQuickPopupItem.

Currently just centerIn is supported, as that's the most common
use case.

[ChangeLog][Controls][Popup] Added anchors.centerIn to Popup to allow
a covenient way of centering a popup.

Task-number: QTBUG-60354
Change-Id: Ia030f812df9da646fea8f373ef6199a21205ffbd
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

1 files changed, 77 insertions, 0 deletions

diff --git a/src/quicktemplates2/qquickpopupanchors_p_p.h b/src/quicktemplates2/qquickpopupanchors_p_p.h
new file mode 100644
index 00000000..c2f577bf
--- /dev/null
+++ b/src/quicktemplates2/qquickpopupanchors_p_p.h
@@ -0,0 +1,77 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the Qt Quick Templates 2 module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL3$
+** 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 The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://www.qt.io/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 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPLv3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or later 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 2.0 requirements will be
+** met: http://www.gnu.org/licenses/gpl-2.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QQUICKPOPUPANCHORS_P_P_H
+#define QQUICKPOPUPANCHORS_P_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/private/qobject_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QQuickPopupAnchors;
+class QQuickPopupPositioner;
+
+class QQuickPopupAnchorsPrivate : public QObjectPrivate
+{
+    Q_DECLARE_PUBLIC(QQuickPopupAnchors)
+
+public:
+    QQuickPopupAnchorsPrivate(QQuickPopupPositioner *positioner);
+    ~QQuickPopupAnchorsPrivate();
+
+    static QQuickPopupAnchorsPrivate *get(QQuickPopupAnchors *popupAnchors)
+    {
+        return popupAnchors->d_func();
+    }
+
+    QQuickPopupPositioner *positioner = nullptr;
+    QQuickItem *centerIn = nullptr;
+};
+
+QT_END_NAMESPACE
+
+#endif // QQUICKPOPUPANCHORS_P_P_H