// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \page qtquicklayouts-responsive.html
    \title Qt Quick Responsive Layouts
    \brief A guideline to make Qt Quick Layouts adaptive to screen size.

    Layouts are a good technique to make resizable user interfaces. However,
    this approach has its limitations as we cannot shrink and expand items
    limitless without sacrificing usability and aesthetics. At some point, it
    makes more sense to reorganize, remove or add certain elements. Adapting to
    different devices (e.g. phones and tables) and screen orientations
    (landscape or portrait) can be implemented similarly. This is what
    we usually understand as responsive layouts and \l {Qt Quick Layouts}
    provide various APIs to implement them.

    \section1 Static hierarchy, adaptive layout

    Layouts have a hierarchy, which is usually defined by the declarative QML
    code. For some simple responsive layouts, it is sufficient to keep the
    hierarchy unmodified and instead just tweak some of the properties that
    affect layouting.

    \section2 Declarative description

    The simplest approach to change layouting is to modify layout properties
    and \l {Layout} attached properties with small expressions. You can for
    instance use ternary operators in order to modify the layout depending
    on its width.
    \l {Item} properties, such as \l {Item::visible}{Item.visible},
    hiding or showing various parts of the interface, can be modified the same
    way.

    In the following snippet, this concept is used to change a two-column
    layout into a single-column layout if the window width is smaller than a
    certain value.

    \snippet layouts/responsiveDeclarative.qml document

    The resulting layouts look like this, depending on the width of the window.

    \div {class="float-right"}
    \inlineimage simpleProxy.png
                 {Narrow window with stacked layout and wide window with
                 side-by-side layout}
    \enddiv

    Various levels of layouts and items can be nested but \l {Item}{Items} can only be moved within a their \l{Item::parent}{Item.parent}.

    \section2 States

    The same result can be achieved with \l {Qt Quick States}. The upside of
    using states is that the \l {Layout} properties for a specific layout are
    collected at a single point in the QML file (at least the changing ones).
    The previously shown example can be implemented as follows and the result
    looks and behaves the exact same.

    \snippet layouts/responsiveStates.qml document

    \section2 LayoutItemProxy

    A third approach is the application of the \l {LayoutItemProxy}. The
    implementation of the previously shown minimalistic example can be found in
    the type documentation. In contrast to previously shown solutions, the
    \l {LayoutItemProxy} enables the declaration of completely separate layouts
    for various form factors. Especially with more complex layouts this might be
    useful to improve and maintain a reasonable source code structure.

    Note, that the \l{LayoutItemProxy} API is in a technology preview state and might
    be subject to change or removal in future Qt versions.

    \section1 Adaptive hierarchy, adaptive layout

    More complex reconstructions of the layout might require changes to
    the hierarchy. A small stand-alone button in a small layout might be
    combined with other buttons and put into a box of a larger layout. An item
    that is fully visible in one layout, might require a \l {Flickable} in
    another, smaller layout. In this scenario, it is best to rely on the \l {LayoutItemProxy}. The \l {LayoutItemProxy} allows to move \l{Item}{Items} across various hierarchy levels and between different \l{Item::parent}{Item.parent}.

    The \l {Qt Quick Layouts - Responsive Layout Example} shows a case where an
    item is moved between different hierarchy levels, put into a \l {Flickable}
    in one case and on the top level in another layout. The two resulting
    layouts look as follows.

    \div {class="float-right"}
    \image qtquicklayouts-example-responsivelayouts.png
           {Two windows showing numbered grid tiles in different arrangements}
    \enddiv


    \section1 Useful links: Consult your design guidelines

    Many design guidelines offer help and tips to create responsive layouts.
    Implementing the respective techniques is possible with the APIs mentioned
    above. For further information we recommend the following links:

    \list
        \li \l {https://developer.apple.com/design/human-interface-guidelines/layout}{Apple human interface guidelines}
        \li \l {https://m3.material.io/foundations/layout/applying-layout/window-size-classes}{Material3 layouts}
        \li \l {https://learn.microsoft.com/en-us/windows/apps/design/layout/responsive-design}{Microsoft Fluent responsive design techniques}
    \endlist

*/
