Add valueRole API to ComboBox

This allows the user to conveniently manage data for a role associated with
the text role. A common example of this is an enum stored in a backend with
nicely formatted text displayed to the user. Before this patch, developers
would have to write code like this:

    ComboBox {
        textRole: "text"
        onActivated: backend.modifier = model[currentIndex].value
        Component.onCompleted: currentIndex = findValue(backend.modifier)
        model: [
            { value: Qt.NoModifier, text: qsTr("No modifier") },
            { value: Qt.ShiftModifier, text: qsTr("Shift") },
            { value: Qt.ControlModifier, text: qsTr("Control") }
        ]

        function findValue(value) {
            for (var i = 0; i < model.length; ++i) {
                if (model[i].value === value)
                    return i
            }
            return -1
        }
    }

With this patch, the code becomes much simpler:

    ComboBox {
        textRole: "text"
        valueRole: "value"
        onActivated: backend.modifier = currentValue
        Component.onCompleted: currentIndex = indexOfValue(backend.modifier)
        model: [
            { value: Qt.NoModifier, text: qsTr("No modifier") },
            { value: Qt.ShiftModifier, text: qsTr("Shift") },
            { value: Qt.ControlModifier, text: qsTr("Control") }
        ]
    }

[ChangeLog][Controls][ComboBox] Added valueRole, currentValue and
indexOfValue(). These allow convenient management of data for a role
associated with the text role.

Change-Id: I0ed19bd0ba9cf6b044a8113ff1a8782d43065449
Fixes: QTBUG-73491
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

6 files changed, 89 insertions, 31 deletions

diff --git a/src/imports/controls/ComboBox.qml b/src/imports/controls/ComboBox.qml
index 3bca9c02..8eefc686 100644
--- a/src/imports/controls/ComboBox.qml
+++ b/src/imports/controls/ComboBox.qml
@@ -34,11 +34,11 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import QtQuick.Controls 2.12
-import QtQuick.Controls.impl 2.12
-import QtQuick.Templates 2.12 as T
+import QtQuick 2.14
+import QtQuick.Window 2.14
+import QtQuick.Controls 2.14
+import QtQuick.Controls.impl 2.14
+import QtQuick.Templates 2.14 as T
 
 T.ComboBox {
     id: control
diff --git a/src/imports/controls/doc/snippets/qtquickcontrols2-combobox-valuerole.qml b/src/imports/controls/doc/snippets/qtquickcontrols2-combobox-valuerole.qml
new file mode 100644
index 00000000..4d7ae3d3
--- /dev/null
+++ b/src/imports/controls/doc/snippets/qtquickcontrols2-combobox-valuerole.qml
@@ -0,0 +1,58 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 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 2.14
+import QtQuick.Controls 2.14
+
+//! [file]
+ApplicationWindow {
+    width: 640
+    height: 480
+    visible: true
+
+    // Used as an example of a backend - this would usually be
+    // e.g. a C++ type exposed to QML.
+    QtObject {
+        id: backend
+        property int modifier
+    }
+
+    ComboBox {
+        textRole: "text"
+        valueRole: "value"
+        // When an item is selected, update the backend.
+        onActivated: backend.modifier = currentValue
+        // Set the initial currentIndex to the value stored in the backend.
+        Component.onCompleted: currentIndex = indexOfValue(backend.modifier)
+        model: [
+            { value: Qt.NoModifier, text: qsTr("No modifier") },
+            { value: Qt.ShiftModifier, text: qsTr("Shift") },
+            { value: Qt.ControlModifier, text: qsTr("Control") }
+        ]
+    }
+}
+//! [file]
diff --git a/src/imports/controls/fusion/ComboBox.qml b/src/imports/controls/fusion/ComboBox.qml
index 3ecb0cf2..58764809 100644
--- a/src/imports/controls/fusion/ComboBox.qml
+++ b/src/imports/controls/fusion/ComboBox.qml
@@ -34,13 +34,13 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import QtQuick.Templates 2.12 as T
-import QtQuick.Controls 2.12
-import QtQuick.Controls.impl 2.12
-import QtQuick.Controls.Fusion 2.12
-import QtQuick.Controls.Fusion.impl 2.12
+import QtQuick 2.14
+import QtQuick.Window 2.14
+import QtQuick.Templates 2.14 as T
+import QtQuick.Controls 2.14
+import QtQuick.Controls.impl 2.14
+import QtQuick.Controls.Fusion 2.14
+import QtQuick.Controls.Fusion.impl 2.14
 
 T.ComboBox {
     id: control
diff --git a/src/imports/controls/imagine/ComboBox.qml b/src/imports/controls/imagine/ComboBox.qml
index 3a3ae682..2d582e98 100644
--- a/src/imports/controls/imagine/ComboBox.qml
+++ b/src/imports/controls/imagine/ComboBox.qml
@@ -34,12 +34,12 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import QtQuick.Templates 2.12 as T
-import QtQuick.Controls 2.12
-import QtQuick.Controls.Imagine 2.12
-import QtQuick.Controls.Imagine.impl 2.12
+import QtQuick 2.14
+import QtQuick.Window 2.14
+import QtQuick.Templates 2.14 as T
+import QtQuick.Controls 2.14
+import QtQuick.Controls.Imagine 2.14
+import QtQuick.Controls.Imagine.impl 2.14
 
 T.ComboBox {
     id: control
diff --git a/src/imports/controls/material/ComboBox.qml b/src/imports/controls/material/ComboBox.qml
index 223f8fca..7d635902 100644
--- a/src/imports/controls/material/ComboBox.qml
+++ b/src/imports/controls/material/ComboBox.qml
@@ -34,13 +34,13 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import QtQuick.Controls 2.12
-import QtQuick.Controls.impl 2.12
-import QtQuick.Templates 2.12 as T
-import QtQuick.Controls.Material 2.12
-import QtQuick.Controls.Material.impl 2.12
+import QtQuick 2.14
+import QtQuick.Window 2.14
+import QtQuick.Controls 2.14
+import QtQuick.Controls.impl 2.14
+import QtQuick.Templates 2.14 as T
+import QtQuick.Controls.Material 2.14
+import QtQuick.Controls.Material.impl 2.14
 
 T.ComboBox {
     id: control
diff --git a/src/imports/controls/universal/ComboBox.qml b/src/imports/controls/universal/ComboBox.qml
index 3ec7e98b..9a4e119b 100644
--- a/src/imports/controls/universal/ComboBox.qml
+++ b/src/imports/controls/universal/ComboBox.qml
@@ -34,12 +34,12 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
-import QtQuick.Window 2.12
-import QtQuick.Controls 2.12
-import QtQuick.Controls.impl 2.12
-import QtQuick.Templates 2.12 as T
-import QtQuick.Controls.Universal 2.12
+import QtQuick 2.14
+import QtQuick.Window 2.14
+import QtQuick.Controls 2.14
+import QtQuick.Controls.impl 2.14
+import QtQuick.Templates 2.14 as T
+import QtQuick.Controls.Universal 2.14
 
 T.ComboBox {
     id: control