/****************************************************************************
**
** Copyright (C) 2017 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.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \page qtquickcontrols2-differences.html
    \title Differences between Qt Quick Controls

    Qt Quick Controls were originally developed to support desktop platforms,
    with mobile and embedded support coming shortly afterwards. They have a
    very broad scope, in that they provide a styling system flexible enough to
    allow the development of applications that have either a platform-dependent
    or platform-independent style.

    On embedded systems, where the hardware has limited resources, this approach
    can be inefficient. Qt Quick Controls 2 were designed to solve this problem,
    using
    \l {https://blog.qt.io/blog/2015/03/31/qt-quick-controls-for-embedded/}{benchmarks}
    to guide the development.

    \section2 C++ and QML

    In many cases, the internal state of a control can be more efficiently
    processed in C++. For example, handling input events in C++ makes a
    difference for controls that would otherwise need to create internal
    MouseAreas and attached Keys objects.

    \section2 Styles

    Not only does handling events and logic in C++ increase performance, but it
    allows the visual QML layer to be a simple, declarative layer on top. This
    is reflected in the structure of the controls project: all visual
    implementations sit in the \e imports folder, so that users who want to
    create their own complete style can copy the folder and start tweaking.
    Read more about implementing a style plugin
    \l {Creating a Custom Style}{here}.

    In Qt Quick Controls 2, styles no longer provide components that are
    dynamically instantiated by controls, but controls themselves consist of
    item delegates that can be replaced. In effect, this means that delegates
    are Qt Quick items that are instantiated on the spot, as properties of the
    control, and are simply parented to the control.

    \section2 Modularity and Simplicity

    When it comes to more complex controls, it is sometimes better to split
    them up into separate building blocks. As an example, the complex
    ScrollView control:

    \qml
    ScrollView {
        horizontalScrollBarPolicy: Qt.ScrollBarAlwaysOff
        Flickable {
            // ...
        }
    }
    \endqml

    Is replaced with simple ScrollBar/ScrollIndicator controls that can be
    attached to any Flickable:

    \qml
    Flickable {
        // ...
        ScrollBar.vertical: ScrollBar { }
    }
    \endqml

    The API of Qt Quick Controls 2 aims to be clean and simple. Common
    operations are easy, and more advanced ones are liberally documented with
    snippets that can be copied into your code.

    \section2 Feature Comparison Table

    \table
    \header
        \li
        \li Qt Quick Controls
        \li Qt Quick Controls 2
    \row
        \li Stylable delegates
        \li Yes
        \li Yes
    \row
        \li Pre-built native styles
        \li Yes
        \li No
    \row
        \li Runtime style/theme changes
        \li Yes \sup 1
        \li Yes \sup 2
    \row
        \li Can be used on Desktop
        \li Yes
        \li Yes
    \row
        \li Can be used on Mobile
        \li Yes \sup 3
        \li Yes
    \row
        \li Can be used on Embedded
        \li Yes \sup 3
        \li Yes
    \row
        \li Internal event handling
        \li QML
        \li C++
    \endtable

    \list 1
    \li Not officially supported, but technically possible via private APIs
    \li Only themes for specific styles can be changed at runtime, styles are fixed
    \li Performance may not be optimal
    \endlist

    \section2 Porting Qt Quick Controls Code

    The API of Qt Quick Controls 2 is very similar to Qt Quick Controls, but it
    does come with some changes necessary to facilitate the improvements. The
    majority of changes are to do with styling; all of a control's delegates
    are now accessible in the control itself, instead of in a separate style
    object.

    For example, to style a button in Qt Quick Controls:

    \badcode
    Button {
        style: ButtonStyle {
            label: Label {
                // ...
            }
        }
    }
    \endcode

    To style a button in Qt Quick Controls 2:

    \qml
    Button {
        contentItem: Label {
            // ...
        }
    }
    \endqml

    \section3 Preparing for Migration

    With this in mind, a good way to prepare for a migration to Qt Quick
    Controls 2 is to place each control that you have a custom style for in its
    own QML file. For example, the Qt Quick Controls button above could be
    moved to a file named \c Button.qml in a directory named \c controls, and
    used in the following manner:

    \badcode
    import "controls" as Controls

    Controls.Button {
        ...
    }
    \endcode

    This works with both modules, and will reduce the amount of work needed
    when the migration begins.

    \section2 Type Comparison Table

    The first column lists all types available in \l {Qt Quick Controls}
    {Qt Quick Controls 1}, \l {Qt Quick Dialogs}, and \l {Qt Quick Extras}.
    The second column documents the respective type in Qt Quick Controls 2.
    When a direct alternative is not available, the third column contains
    an alternative that provides related functionality. The last column
    contains some remarks about the differences between the types in the
    different modules.

    \table
    \header
        \li Qt Quick Controls 1
        \li Qt Quick Controls 2
        \li Alternatives
        \li Remarks
    \row
        \li \l [QML QtQuickControls] {Action}
        \li \mdash
        \li \l [QML QtQuick] {Shortcut} \br\sup {(Qt Quick)}
        \li \list
                \li \b {Qt Quick Controls 1}: \c Action is an abstract user interface
                    action that is bound to buttons and menu items, and can provide
                    shortcuts.
                \li \b {Qt Quick}: \c Shortcut provides the shortcut functionality that
                    was previously only provided by \c Action.
            \endlist
    \row
        \li \l [QML QtQuickControls] {ApplicationWindow}
        \li \l [QML QtQuickControls2] {ApplicationWindow}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {BusyIndicator}
        \li \l [QML QtQuickControls2] {BusyIndicator}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {Button}
        \li \l [QML QtQuickControls2] {Button}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {Calendar}
        \li \mdash
        \li \l [QML QtLabsCalendar] {MonthGrid},\br
            \l [QML QtLabsCalendar] {DayOfWeekRow},\br
            \l [QML QtLabsCalendar] {WeekNumberColumn} \br\sup {(Qt Labs Calendar)}
        \li \list
                \li \b {Qt Labs Calendar}: \c MonthGrid, \c DayOfWeek, and \c WeekNumberColumn
                    are \e experimental unstyled building blocks for calendar views.
            \endlist
    \row
        \li \l [QML QtQuickControls] {CheckBox}
        \li \l [QML QtQuickControls2] {CheckBox}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {ComboBox}
        \li \l [QML QtQuickControls2] {ComboBox}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {ExclusiveGroup}
        \li \mdash
        \li \l [QML QtQuickControls2] {ButtonGroup} \br\sup {(Qt Quick Controls 2)}
        \li \list
                \li \b {Qt Quick Controls 2}: \c ButtonGroup offers similar functionality.
            \endlist
    \row
        \li \l [QML QtQuickControls] {GroupBox}
        \li \l [QML QtQuickControls2] {GroupBox}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {Label}
        \li \l [QML QtQuickControls2] {Label}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {Menu}
        \li \l [QML QtQuickControls2] {Menu}
        \li \l [QML QtLabsPlatform] {Menu} \br\sup {(Qt Labs Platform)}
        \li \list
                \li \b {Qt Quick Controls 1}: \c Menu is native on platforms where an
                    implementation is available in the Qt Platform Abstraction Layer.
                    Other platforms use a QML-based top-level menu popup window. \c Menu
                    supports traditional desktop style cascading submenus, but does not
                    work on Embedded Linux because \l EGLFS does not support multiple
                    top-level windows.
                \li \b {Qt Quick Controls 2}: \c Menu is a non-native \c Item-based popup
                    that is stacked above the application content. Due to this, menu popups
                    are restricted within window boundaries. \c Menu is fully customizable
                    using QML and Qt Quick, and allows adding any \c Items. Traditional
                    desktop oriented features, such as cascading submenus and visualizing
                    keyboard shortcuts are missing.
                \li \b {Qt Labs Platform}: \c Menu is an \e experimental native menu that
                    uses Qt Widgets as a fallback on platforms where a native implementation
                    is not available in the Qt Platform Abstraction Layer.
            \endlist
    \row
        \li \l [QML QtQuickControls] {MenuBar}
        \li \mdash
        \li \l [QML QtLabsPlatform] {MenuBar} \br\sup {(Qt Labs Platform)}
        \li \list
                \li \b {Qt Quick Controls 1}: \c MenuBar is native on platforms where an
                    implementation is available in the Qt Platform Abstraction Layer. Other
                    platforms use a QML-based menubar item stacked at the top of the window.
                \li \b {Qt Labs Platform}: \c MenuBar is an \e experimental native menubar.
                    It is only available on platforms where a native implementation is available
                    in the Qt Platform Abstraction Layer.
            \endlist
    \row
        \li \l [QML QtQuickControls] {MenuItem},\br
            \l [QML QtQuickControls] {MenuSeparator}
        \li \l [QML QtQuickControls2] {MenuItem},\br
            \l [QML QtQuickControls2] {MenuSeparator}
        \li \l [QML QtLabsPlatform] {MenuItem},\br
            \l [QML QtLabsPlatform] {MenuSeparator} \br\sup {(Qt Labs Platform)}
        \li \list
                \li \b {Qt Quick Controls 1}: \c MenuItem and \c MenuSeparator are native
                    on platforms where an implementation is available in the Qt Platform
                    Abstraction Layer. Other platforms use QML-based menu items and separators.
                \li \b {Qt Quick Controls 2}: \c MenuItem and \c MenuSeparator are a non-native
                    QML-based menu items and separators that can be fully customized using QML
                    and Qt Quick.
                \li \b {Qt Labs Platform}: \c MenuItem and \c MenuSeparator are \e experimental
                    native menu items and separators.
            \endlist
    \row
        \li \l [QML QtQuickControls] {ProgressBar}
        \li \l [QML QtQuickControls2] {ProgressBar}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {RadioButton}
        \li \l [QML QtQuickControls2] {RadioButton}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {ScrollView}
        \li \l [QML QtQuickControls2] {ScrollView}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {Slider}
        \li \l [QML QtQuickControls2] {Slider}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {SpinBox}
        \li \l [QML QtQuickControls2] {SpinBox}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {SplitView}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {StackView},\br
            \l [QML QtQuickControls] {StackViewDelegate},\br
            \l [QML QtQuickControls] {Stack}
        \li \l [QML QtQuickControls2] {StackView}
        \li
        \li \list
                \li \b {Qt Quick Controls 2}: \c StackView provides customizable transitions
                    and attached properties via a single \c StackView type.
            \endlist
    \row
        \li \l [QML QtQuickControls] {StatusBar}
        \li \mdash
        \li \l [QML QtQuickControls2] {ToolBar} \br\sup {(Qt Quick Controls 2)}
        \li \list
                \li \b {Qt Quick Controls 2}: \c ApplicationWindow allows assigning any
                    item or control, such as \c ToolBar, as a header or footer.
            \endlist
    \row
        \li \l [QML QtQuickControls] {Switch}
        \li \l [QML QtQuickControls2] {Switch}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {TabView},\br
            \l [QML QtQuickControls] {Tab}
        \li \mdash
        \li \l [QML QtQuickControls2] {TabBar},\br
            \l [QML QtQuickControls2] {TabButton} \br\sup {(Qt Quick Controls 2)}
        \li \list
                \li \b {Qt Quick Controls 2}: \c TabBar and \c TabButton offer similar
                    functionality, and can be used to build tabbed views.
            \endlist
    \row
        \li \l [QML QtQuickControls] {TableView}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {TextArea}
        \li \l [QML QtQuickControls2] {TextArea}
        \li
        \li \list
                \li \b {Qt Quick Controls 1}: \c TextArea inherits \c ScrollView and is therefore
                    always a scrollable editor.
                \li \b {Qt Quick Controls 2}: \c TextArea is a simpler multi-line editor that can
                    be optionally attached to a \c Flickable to provide scrolling functionality.
                    This allows using \c TextArea in a scrollable page without having two nested
                    scrollable areas, which can be problematic and cause usability issues.
            \endlist
    \row
        \li \l [QML QtQuickControls] {TextField}
        \li \l [QML QtQuickControls2] {TextField}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {ToolBar}
        \li \l [QML QtQuickControls2] {ToolBar}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {ToolButton}
        \li \l [QML QtQuickControls2] {ToolButton}
        \li
        \li
    \row
        \li \l [QML QtQuickControls] {TreeView}
        \li \mdash
        \li
        \li

    \header
        \li Qt Quick Dialogs
        \li Qt Quick Controls 2
        \li Alternatives
        \li Remarks
    \row
        \li \l [QML QtQuickDialogs] {Dialog}
        \li \mdash
        \li \l [QML QtQuickControls2] {Dialog}
        \li \list
                \li \b {Qt Quick Dialogs}: \c Dialog is either a top-level window or an \c Item-based popup
                    depending on whether the underlying platform supports multiple top-level windows.
                \li \b {Qt Quick Controls 2}: \c Dialog is not a top-level window, but an \c Item-based
                    popup that is stacked above the application content. Due to this, dialogs are restricted
                    within window boundaries.
            \endlist
    \row
        \li \l [QML QtQuickDialogs] {ColorDialog},\br
            \l [QML QtQuickDialogs] {FileDialog},\br
            \l [QML QtQuickDialogs] {FontDialog},\br
            \l [QML QtQuickDialogs] {MessageDialog}
        \li \mdash
        \li \l [QML QtLabsPlatform] {ColorDialog},\br
            \l [QML QtLabsPlatform] {FileDialog},\br
            \l [QML QtLabsPlatform] {FolderDialog},\br
            \l [QML QtLabsPlatform] {FontDialog},\br
            \l [QML QtLabsPlatform] {MessageDialog} \br\sup {(Qt Labs Platform)}
        \li \list
                \li \b {Qt Quick Dialogs}: Dialogs are native on platforms where an implementation
                    is available in the Qt Platform Abstraction Layer. Other platforms use either
                    Qt Widgets or QML-based dialogs depending on whether the underlying platform
                    supports multiple top-level windows.
                \li \b {Qt Labs Platform}: \e Experimental native dialogs that use Qt Widgets as
                    a fallback on platforms where a native implementation is not available in the
                    Qt Platform Abstraction Layer.
            \endlist

    \header
        \li Qt Quick Extras
        \li Qt Quick Controls 2
        \li Alternatives
        \li Remarks
    \row
        \li \l [QML QtQuickExtras] {CircularGauge}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {DelayButton}
        \li \l [QML QtQuickControls2] {DelayButton}
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {Dial}
        \li \l [QML QtQuickControls2] {Dial}
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {Gauge}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {Picture}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {PieMenu}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {StatusIndicator}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {ToggleButton}
        \li \mdash
        \li
        \li
    \row
        \li \l [QML QtQuickExtras] {Tumbler},\br
            \l [QML QtQuickExtras] {TumblerColumn}
        \li \l [QML QtQuickControls2] {Tumbler}
        \li
        \li \list
                \li \b {Qt Quick Extras}: \c Tumbler can consist of multiple columns.
                \li \b {Qt Quick Controls 2}: \c Tumbler presents a single spinnable wheel.
                    Multiple columns can be created by placing multiple \c Tumblers next
                    to each other.
            \endlist

    \header
        \li No Predecessor
        \li Qt Quick Controls 2
        \li Alternatives
        \li Remarks
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {AbstractButton}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {ButtonGroup}
        \li \l [QML QtQuickControls] {ExclusiveGroup} \br\sup {(Qt Quick Controls 1)}
        \li \list
                \li \b {Qt Quick Controls 1}: \c ExclusiveGroup offers similar functionality.
            \endlist
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {CheckDelegate}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {Container}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {Control}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {Drawer}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {Frame}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {ItemDelegate}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {Page}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {PageIndicator}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {Pane}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {Popup}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {RadioDelegate}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {RangeSlider}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {RoundButton}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {ScrollBar},\br
            \l [QML QtQuickControls2] {ScrollIndicator}
        \li \l [QML QtQuickControls] {ScrollView} \br\sup {(Qt Quick Controls 1)}
        \li \list
                \li \b {Qt Quick Controls 1}: \c ScrollView offers similar functionality.
                    It combines horizontal and vertical scrollbars, and the background and
                    frame around the scrollable view.
            \endlist
    \row
        \li \mdash
        \li \mdash
        \li \l [QML QtLabsPlatform] {StandardPaths} \br\sup {(Qt Labs Platform)}
        \li \list
                \li \b {Qt Quick Dialogs}: \c FileDialog offers a shortcut property that can be used
                    to access the most common standard paths.
                \li \b {Qt Labs Platform}: \c StandardPaths offers a separate type to give full access
                    to the standard paths.
            \endlist
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {SwipeDelegate}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {SwipeView}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {SwitchDelegate}
        \li
        \li
    \row
        \li \mdash
        \li \mdash
        \li \l [QML QtLabsPlatform] {SystemTrayIcon} \br\sup {(Qt Labs Platform)}
        \li \list
                \li \b {Qt Labs Platform}: \c SystemTrayIcon is an \e experimental native
                    system tray icon that uses Qt Widgets as a fallback on platforms where
                    a native implementation is not available in the Qt Platform Abstraction
                    Layer.
            \endlist
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {TabBar},\br
            \l [QML QtQuickControls2] {TabButton}
        \li \l [QML QtQuickControls] {TabView} \br\sup {(Qt Quick Controls 1)}
        \li \list
                \li \b {Qt Quick Controls 1}: \c TabView offers similar functionality.
                    It combines the tab bar, background and frame around the tabs.
            \endlist
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {ToolSeparator}
        \li
        \li
    \row
        \li \mdash
        \li \l [QML QtQuickControls2] {ToolTip}
        \li
        \li \list
                \li \b {Qt Quick Controls 1}: \c Button and \c Action have built-in
                    Qt Widgets-based tooltips.
                \li \b {Qt Quick Controls 2}: \c ToolTip can be attached to any \c Item.
            \endlist
    \endtable

    \section1 Related Information

    \list
      \li \l{Qt Quick}
      \li \l{Qt Quick Controls 2 QML Types}
      \li \l{Qt Quick Controls QML Types}
      \li \l{Qt Quick Extras QML Types}
      \li \l{Qt Labs Calendar QML Types}
      \li \l{Qt Labs Platform QML Types}
    \endlist
*/
