Improve visibility into Positioner positioning from QML

Add a forceLayout function, similar to the views, as well
as a signal that indicates when positioning has completed.

Change-Id: Ice01ea0840c707e403fdd4ea59d92a89e2ed8e4b
Task-number: QTBUG-44762
Task-number: QTBUG-32114
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

4 files changed, 175 insertions, 0 deletions

diff --git a/src/quick/items/qquickitemsmodule.cpp b/src/quick/items/qquickitemsmodule.cpp
index 0b325d7fa8..5bba52ed73 100644
--- a/src/quick/items/qquickitemsmodule.cpp
+++ b/src/quick/items/qquickitemsmodule.cpp
@@ -380,6 +380,10 @@ static void qt_quickitems_defineModule(const char *uri, int major, int minor)
     qmlRegisterType<QQuickTouchPoint>(uri, 2, 9, "TouchPoint");
     qRegisterMetaType<QPointingDeviceUniqueId>("QPointingDeviceUniqueId");
     qmlRegisterUncreatableType<QPointingDeviceUniqueId>(uri, 2, 9, "PointingDeviceUniqueId", QQuickTouchPoint::tr("PointingDeviceUniqueId is only available via read-only properties"));
+#if QT_CONFIG(quick_positioners)
+    qmlRegisterUncreatableType<QQuickBasePositioner, 9>(uri, 2, 9, "Positioner",
+                                                  QStringLiteral("Positioner is an abstract type that is only available as an attached property."));
+#endif
 }
 
 static void initResources()
diff --git a/src/quick/items/qquickpositioners.cpp b/src/quick/items/qquickpositioners.cpp
index 0287fdd45c..05d3ae0191 100644
--- a/src/quick/items/qquickpositioners.cpp
+++ b/src/quick/items/qquickpositioners.cpp
@@ -290,6 +290,11 @@ void QQuickBasePositioner::itemChange(ItemChange change, const ItemChangeData &v
     QQuickItem::itemChange(change, value);
 }
 
+void QQuickBasePositioner::forceLayout()
+{
+    updatePolish();
+}
+
 void QQuickBasePositioner::prePositioning()
 {
     Q_D(QQuickBasePositioner);
@@ -401,6 +406,8 @@ void QQuickBasePositioner::prePositioning()
 
     //Set implicit size to the size of its children
     setImplicitSize(contentSize.width(), contentSize.height());
+
+    emit positioningComplete();
 }
 
 void QQuickBasePositioner::positionItem(qreal x, qreal y, PositionedItem *target)
@@ -910,6 +917,28 @@ void QQuickPositionerAttached::setIsLastItem(bool isLastItem)
 
   \sa Grid::spacing
 */
+/*!
+    \qmlmethod QtQuick::Column::forceLayout()
+    \since 5.9
+
+    Column typically positions its children once per frame. This means that
+    inside script blocks it is possible for the underlying children to have changed,
+    but the Column to have not yet been updated accordingly.
+
+    This method forces the Column to immediately respond to any outstanding
+    changes in its children.
+
+    \b Note: methods in general should only be called after the Component has completed.
+*/
+/*!
+    \qmlsignal QtQuick::Column::positioningComplete()
+    \since 5.9
+
+    This signal is emitted when positioning has been completed.
+
+    The corresponding handler is \c onPositioningComplete.
+*/
+
 QQuickColumn::QQuickColumn(QQuickItem *parent)
 : QQuickBasePositioner(Vertical, parent)
 {
@@ -1077,6 +1106,27 @@ void QQuickColumn::reportConflictingAnchors()
 
   \sa Grid::spacing
 */
+/*!
+    \qmlmethod QtQuick::Row::forceLayout()
+    \since 5.9
+
+    Row typically positions its children once per frame. This means that
+    inside script blocks it is possible for the underlying children to have changed,
+    but the Row to have not yet been updated accordingly.
+
+    This method forces the Row to immediately respond to any outstanding
+    changes in its children.
+
+    \b Note: methods in general should only be called after the Component has completed.
+*/
+/*!
+    \qmlsignal QtQuick::Row::positioningComplete()
+    \since 5.9
+
+    This signal is emitted when positioning has been completed.
+
+    The corresponding handler is \c onPositioningComplete.
+*/
 
 class QQuickRowPrivate : public QQuickBasePositionerPrivate
 {
@@ -1355,6 +1405,27 @@ void QQuickRow::reportConflictingAnchors()
 
   \sa rows, columns
 */
+/*!
+    \qmlmethod QtQuick::Grid::forceLayout()
+    \since 5.9
+
+    Grid typically positions its children once per frame. This means that
+    inside script blocks it is possible for the underlying children to have changed,
+    but the Grid to have not yet been updated accordingly.
+
+    This method forces the Grid to immediately respond to any outstanding
+    changes in its children.
+
+    \b Note: methods in general should only be called after the Component has completed.
+*/
+/*!
+    \qmlsignal QtQuick::Grid::positioningComplete()
+    \since 5.9
+
+    This signal is emitted when positioning has been completed.
+
+    The corresponding handler is \c onPositioningComplete.
+*/
 
 class QQuickGridPrivate : public QQuickBasePositionerPrivate
 {
@@ -1920,6 +1991,28 @@ void QQuickGrid::reportConflictingAnchors()
 
   \sa Grid::spacing
 */
+/*!
+    \qmlmethod QtQuick::Flow::forceLayout()
+    \since 5.9
+
+    Flow typically positions its children once per frame. This means that
+    inside script blocks it is possible for the underlying children to have changed,
+    but the Flow to have not yet been updated accordingly.
+
+    This method forces the Flow to immediately respond to any outstanding
+    changes in its children.
+
+
+    \b Note: methods in general should only be called after the Component has completed.
+*/
+/*!
+    \qmlsignal QtQuick::Flow::positioningComplete()
+    \since 5.9
+
+    This signal is emitted when positioning has been completed.
+
+    The corresponding handler is \c onPositioningComplete.
+*/
 
 class QQuickFlowPrivate : public QQuickBasePositionerPrivate
 {
diff --git a/src/quick/items/qquickpositioners_p.h b/src/quick/items/qquickpositioners_p.h
index c25ecd6dbc..ae6e795794 100644
--- a/src/quick/items/qquickpositioners_p.h
+++ b/src/quick/items/qquickpositioners_p.h
@@ -155,6 +155,8 @@ public:
     void setBottomPadding(qreal padding);
     void resetBottomPadding();
 
+    Q_REVISION(9) Q_INVOKABLE void forceLayout();
+
 protected:
     QQuickBasePositioner(QQuickBasePositionerPrivate &dd, PositionerType at, QQuickItem *parent);
     void componentComplete() Q_DECL_OVERRIDE;
@@ -172,6 +174,7 @@ Q_SIGNALS:
     Q_REVISION(6) void leftPaddingChanged();
     Q_REVISION(6) void rightPaddingChanged();
     Q_REVISION(6) void bottomPaddingChanged();
+    Q_REVISION(9) void positioningComplete();
 
 protected Q_SLOTS:
     void prePositioning();
diff --git a/tests/auto/qmltest/positioners/tst_positioners.qml b/tests/auto/qmltest/positioners/tst_positioners.qml
new file mode 100644
index 0000000000..03a0e13225
--- /dev/null
+++ b/tests/auto/qmltest/positioners/tst_positioners.qml
@@ -0,0 +1,75 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.9
+import QtTest 1.1
+
+Item {
+    Column {
+        id: column
+        Repeater {
+            id: repeater
+            model: 2
+            Rectangle {
+                width: 100
+                height: 30
+                border.width: 1
+            }
+        }
+    }
+
+    SignalSpy {
+        id: spy
+        target: column
+        signalName: "positioningComplete"
+    }
+
+    TestCase {
+        function test_forceLayout() {
+            compare(column.height, 60)
+            repeater.model = 4
+            column.forceLayout()
+            compare(column.height, 120)
+
+            // initial positioning and our forced layout
+            compare(spy.count, 2)
+        }
+    }
+}