Add SplitView

SplitView is an important tool for desktop applications that do not
want to use a dock widget-style approach for their user interface.
It allows users to have some degree of control over the sizing of
elements in the UI, as well as the ability to conveniently serialize
those sizes so that they're remembered across sessions.

The main differences between this and the SplitView in
Qt Quick Controls 1 are:

- Has its own SplitView attached properties, rather than relying on
  the Layout attached properties (which required an additional import).
- Uses the attached preferredWidth and preferredHeight properties
  as well as Item's implicitWidth/implicitHeight properties
  for the preferred size of items, rather than using the width and
  height properties.
- Inherits from Container, so supports most of its API (though some
  parts of the API, like the currentIndex-related stuff, make no
  sense for SplitView).
- Uses attached SplitHandle properties for the handle delegate to
  visualize hovered/pressed effects.
- Offers convenience API for serializing the user's preferred sizes.

[ChangeLog][Controls][SplitView] Introduced SplitView, a control that
lays out items horizontally or vertically with a draggable splitter
between each item.

Task-number: QTBUG-56318
Change-Id: I3da91643ab312eb9ef5b0567da4e758f17747192
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

3 files changed, 66 insertions, 0 deletions

diff --git a/src/imports/controls/doc/images/qtquickcontrols2-splitview-custom.png b/src/imports/controls/doc/images/qtquickcontrols2-splitview-custom.png
new file mode 100644
index 00000000..7afd3ff8
--- /dev/null
+++ b/src/imports/controls/doc/images/qtquickcontrols2-splitview-custom.png
diff --git a/src/imports/controls/doc/snippets/qtquickcontrols2-splitview-custom.qml b/src/imports/controls/doc/snippets/qtquickcontrols2-splitview-custom.qml
new file mode 100644
index 00000000..e202e836
--- /dev/null
+++ b/src/imports/controls/doc/snippets/qtquickcontrols2-splitview-custom.qml
@@ -0,0 +1,57 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** 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 https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file. Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.12
+import QtQuick.Controls 2.5
+
+Item {
+    width: 200
+    height: 100
+
+    //! [1]
+    SplitView {
+        id: splitView
+        anchors.fill: parent
+
+        handle: Rectangle {
+            implicitWidth: 4
+            implicitHeight: 4
+            color: SplitHandle.pressed ? "#81e889"
+                : (SplitHandle.hovered ? Qt.lighter("#c2f4c6", 1.1) : "#c2f4c6")
+        }
+
+        Rectangle {
+            implicitWidth: 150
+            color: "#444"
+        }
+        Rectangle {
+            implicitWidth: 50
+            color: "#666"
+        }
+    }
+    //! [1]
+}
diff --git a/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc b/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc
index cabeb528..de13be9d 100644
--- a/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc
+++ b/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc
@@ -736,6 +736,15 @@
         \snippet qtquickcontrols2-spinbox-custom.qml file
 
 
+    \section2 Customizing SplitView
+
+        SplitView consists of a visual \l {SplitView::handle}{handle} delegate.
+
+        \image qtquickcontrols2-splitview-custom.png
+
+        \snippet qtquickcontrols2-splitview-custom.qml 1
+
+
     \section2 Customizing StackView
 
         StackView can have a visual \l {Control::background}{background}