improve documentation of DragHandler

Change-Id: Ifde67ba567b447da948b79d32676458fd0628ec5
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

4 files changed, 210 insertions, 2 deletions

diff --git a/src/quick/doc/snippets/pointerHandlers/dragHandler.qml b/src/quick/doc/snippets/pointerHandlers/dragHandler.qml
new file mode 100644
index 0000000000..349cdcb95f
--- /dev/null
+++ b/src/quick/doc/snippets/pointerHandlers/dragHandler.qml
@@ -0,0 +1,50 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the documentation 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."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick 2.10
+import Qt.labs.handlers 1.0
+
+Rectangle {
+    width: 100
+    height: 100
+    color: "lightsteelblue"
+    DragHandler { }
+}
+//![0]
diff --git a/src/quick/doc/snippets/pointerHandlers/dragHandlerDifferentTarget.qml b/src/quick/doc/snippets/pointerHandlers/dragHandlerDifferentTarget.qml
new file mode 100644
index 0000000000..e8f2a04e6a
--- /dev/null
+++ b/src/quick/doc/snippets/pointerHandlers/dragHandlerDifferentTarget.qml
@@ -0,0 +1,62 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the documentation 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."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick 2.10
+import Qt.labs.handlers 1.0
+
+Item {
+    width: 640
+    height: 480
+
+    Rectangle {
+        id: feedback
+        border.color: "red"
+        width: Math.max(10, handler.point.ellipseDiameters.width)
+        height: Math.max(10, handler.point.ellipseDiameters.height)
+        radius: Math.max(width, height) / 2
+        visible: handler.active
+    }
+
+    DragHandler {
+        id: handler
+        target: feedback
+    }
+}
+//![0]
diff --git a/src/quick/doc/snippets/pointerHandlers/dragHandlerNullTarget.qml b/src/quick/doc/snippets/pointerHandlers/dragHandlerNullTarget.qml
new file mode 100644
index 0000000000..e210ce0952
--- /dev/null
+++ b/src/quick/doc/snippets/pointerHandlers/dragHandlerNullTarget.qml
@@ -0,0 +1,60 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the documentation 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."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick 2.10
+import Qt.labs.handlers 1.0
+
+Item {
+    width: 640
+    height: 480
+
+    DragHandler {
+        id: handler
+        target: null
+    }
+
+    Text {
+        color: handler.active ? "darkgreen" : "black"
+        text: handler.point.position.x.toFixed(1) + "," + handler.point.position.y.toFixed(1)
+        x: handler.point.position.x - width / 2
+        y: handler.point.position.y - height
+    }
+}
+//![0]
diff --git a/src/quick/handlers/qquickdraghandler.cpp b/src/quick/handlers/qquickdraghandler.cpp
index 5e7b6a4962..12f1a29bca 100644
--- a/src/quick/handlers/qquickdraghandler.cpp
+++ b/src/quick/handlers/qquickdraghandler.cpp
@@ -46,11 +46,29 @@ QT_BEGIN_NAMESPACE
 /*!
     \qmltype DragHandler
     \instantiates QQuickDragHandler
-    \inqmlmodule QtQuick
+    \inherits SinglePointHandler
+    \inqmlmodule Qt.labs.handlers
     \ingroup qtquick-handlers
     \brief Handler for dragging
 
     DragHandler is a handler that is used to interactively move an Item.
+    Like other Pointer Handlers, by default it is fully functional, and
+    manipulates its \l target.
+
+    \snippet pointerHandlers/dragHandler.qml 0
+
+    It has properties to restrict the range of dragging.
+
+    If it is declared within one Item but is assigned a different \l target,
+    then it handles events within the bounds of the \l parent Item but
+    manipulates the \c target Item instead:
+
+    \snippet pointerHandlers/dragHandlerDifferentTarget.qml 0
+
+    A third way to use it is to set \l target to \c null and react to property
+    changes in some other way:
+
+    \snippet pointerHandlers/dragHandlerNullTarget.qml 0
 
     At this time, drag-and-drop is not yet supported.
 
@@ -172,7 +190,25 @@ void QQuickDragHandler::setTranslation(const QVector2D &trans)
     emit translationChanged();
 }
 
-
+/*!
+    \qmlpropertygroup QtQuick::DragHandler::xAxis
+    \qmlpropertygroup QtQuick::DragHandler::yAxis
+    \qmlproperty real QtQuick::DragHandler::DragAxis::minimum
+    \qmlproperty real QtQuick::DragHandler::DragAxis::maximum
+    \qmlproperty real QtQuick::DragHandler::DragAxis::enabled
+
+    \c xAxis and yAxis control the constraints for horizontal and vertical
+    dragging, respectively.
+
+    \value minimum
+        The minimum acceptable value of \l {Item::x}{x} or \l {Item::y}{y}
+        to be applied to the \l target
+    \value maximum
+        The maximum acceptable value of \l {Item::x}{x} or \l {Item::y}{y}
+        to be applied to the \l target
+    \value enabled
+        Whether dragging in this direction is allowed at all
+*/
 QQuickDragAxis::QQuickDragAxis()
   : m_minimum(-DBL_MAX)
   , m_maximum(DBL_MAX)