path: root/doc/src/qtquick/qtquick-screens.qdoc

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/*!

    \contentspage {Qt Creator Manual}
    \previouspage quick-scalable-image.html
    \page quick-screens.html
    \nextpage quick-export-to-qml.html

    \title Creating Screens

    You can use predefined QML types and your own components to create
    screens. Typically, the main qml file in a Qt Quick project specifies the
    main window of an application.

    The QML files in the project folder are displayed in \gui {QML Components}
    in the \gui Library pane.

    You can also use ready-made Qt Quick 1 Components (for Qt 4) to create
    screens with a native look and feel for a particular target platform.
    Since Qt 5.1, Qt Quick Controls, Dialogs, and Layouts are available for
    creating classic desktop-style user interfaces using Qt Quick 2.1. You can
    use the Qt Quick Controls Styles to customize Qt Quick Controls.

    \section1 Adding Components to Screens

    \list 1

        \li Drag and drop components from the \gui Library pane to the editor.

        \li Select components in the \gui Navigator pane to edit their
            properties in the \gui Properties pane.

            For example, you can anchor components to a position on the screen.

    \endlist


    \section1 Using Data Models

    You can create the following types of views to organize items provided by
    \l{Models and Views in Qt Quick}{data models}:

    \list

        \li GridView provides a grid vizualization of a model.

        \li ListView provides a list vizualization of a model.

        \li PathView visualizes the contents of a model along a path.

    \endlist

    When you add a GridView, ListView, or PathView, the ListModel and the
    delegate component that creates an instance for each item in the model are
    added automatically. You can edit item properties
    in the \gui Properties pane or
    in the code editor. You can also replace the default model and
    delegate with other, more complex models and delegates in the code editor.

    \section1 Positioning Items on Screens

    The position of an item on the canvas can be either absolute or relative
    to other items. If you are designing a static user interface,
    \l{Important Concepts In Qt Quick - Positioning#manual-positioning}
    {manual positioning} provides the most efficient form of positioning items
    on the screen. For a dynamic user interface, you can employ the following
    positioning methods provided by Qt Quick:

    \list

        \li \l{Setting Bindings}

        \li \l{Setting Anchors and Margins}

        \li \l{Using Positioners}

        \li \l{Using Layouts}

        \li \l{Using Split Views}

    \endlist

    \section2 Setting Bindings

    \l{Positioning with Bindings}
    {Property binding} is a declarative way of specifying the value of a property.
    Binding allows a property value to be expressed as a JavaScript expression
    that defines the value relative to other property values or data accessible
    in the application. The property value is automatically kept up to date if
    the other properties or data values change.

    Property bindings are created implicitly in QML whenever a property is
    assigned a JavaScript expression. To set JavaScript expressions as values of
    properties in \QMLD, click the circle icon next to a property to open a
    context menu, and select \gui {Set Binding}.

    \image qmldesigner-set-expression.png "Type properties context menu"

    To remove bindings, select \gui Reset in the context menu.

    For more information on the JavaScript environment provided by QML, see
    \l{Integrating QML and JavaScript}.

    \QMLD cannot show bindings and using them might have a negative impact on
    performance, so consider setting anchors and margins for items, instead.
    For example, instead of setting \c {parent.width} for an item, you could
    anchor the item to its sibling items on the left and the right.

    \section2 Setting Anchors and Margins

    In an \l{Important Concepts In Qt Quick - Positioning#anchors}
    {anchor-based} layout, each QML type can be thought of as having a set of
    invisible \e anchor lines: top, bottom, left, right, fill, horizontal
    center, vertical center, and baseline.

    In the \gui Layout pane you can set anchors and margins for items. To set
    the anchors of an item, click the anchor buttons. You can combine the
    top/bottom, left/right, and horizontal/vertical anchors to anchor items in
    the corners of the parent item or center them horizontally or vertically
    within the parent item.

    \image qmldesigner-anchor-buttons.png "Anchor buttons"

    Specifying the baseline anchor in \QMLD is not supported. You can specify it
    using the code editor.

    For performance reasons, you can only anchor an item to its siblings and
    direct parent. By default, an item is anchored to its parent when you
    use the anchor buttons. Select a sibling of the item in the \gui Target
    field to anchor to it, instead.

    Arbitrary anchoring is not supported. For example, you cannot specify:
    \c {anchor.left: parent.right}. You have to specify: \c {anchor.left: parent.left}.
    When you use the anchor buttons, anchors to the parent item are always
    specified to the same side. However, anchors to sibling items are specified
    to the opposite side: \c {anchor.left: sibling.right}. This allows you to keep
    sibling items together.

    In the following image, \gui{Rectangle 2} is anchored to \gui{Rectangle 1}
    on its left and to the bottom of its parent.

    \image qmldesigner-anchors.png "Anchoring sibling items"

    The anchors for \gui{Rectangle 2} are specified as follows in code:

    \qml
    Rectangle {
        id: rectangle2
        anchors.left: rectangle1.right
        anchors.leftMargin: 15
        anchors.bottom: parent.bottom
        anchors.bottomMargin: 15
        //
    }
    \endqml

    Margins specify the amount of empty space to leave to the outside of an item.
    Margins only have meaning for anchors. They do not take any effect when using
    other layouts or absolute positioning.

    \section2 Using Positioners

    \l{Important Concepts In Qt Quick - Positioning#positioners}
    {Positioner items} are container items that manage the positions of items in
    a declarative user interface. Positioners behave in a similar way to the
    layout managers used with standard Qt widgets, except that they are also
    containers in their own right.

    You can use the following positioners to arrange items on screens:

    \list

        \li \l{Column} arranges its child items vertically.

        \li \l{Row} arranges its child items horizontally.

        \li \l{Grid}
            arranges its child items so that they are aligned in a grid and
            are not overlapping.

        \li \l{Flow}
            arranges its child items side by side, wrapping as necessary.

    \endlist

    To lay out several items in a Column, Row, Grid, or Flow, select
    the items on the canvas, and then select \gui Layout in the context
    menu.

    \section2 Using Layouts

    From Qt 5.1, you can use QML types in the \l{qtquicklayouts-index.html}
    {Qt Quick Layouts} module to arrange Qt Quick items on screens. Unlike
    positioners, they manage both the positions and sizes of items in a
    declarative interface. They are well suited for resizable user interfaces.

    You can use the following layout types to arrange items on screens:

    \list

        \li \l{Layout} provides attached properties for items pushed onto a
            \gui {Column Layout}, \gui {Row Layout}, or \gui {Grid Layout}.

        \li ColumnLayout provides a grid layout with only one column.

        \li RowLayout provides a grid layout with only one row.

        \li GridLayout provides a way of dynamically arranging items in a
            grid.

    \endlist

    To lay out several items in a \gui {Column Layout}, \gui {Row Layout}, or
    \gui {Grid Layout}, select the items on the canvas, and then select
    \gui Layout in the context menu.

    To make an item within a layout as wide as possible while respecting the
    given constraints, select the item on the canvas and then select
    \gui Layout > \gui {Fill Width} in the context menu. To make the item as
    high as possible, select \gui {Fill Height}.

    \section2 Using Split Views

    From Qt 5.1, you can use the SplitView Qt Quick Control to arrange items
    horizontally or vertically
    with a draggable splitter between each item.


    \section1 Using States

    Use states and transitions to navigate between screens.

    QML states typically describe user interface configurations, such as the UI
    controls, their properties and behavior and the available actions. For
    example, you can use states to create two screens.

    To add states, click the empty slot in the \gui States pane. Then modify the
    new state in the visual editor.

    \image qmldesigner-states.png "States pane"

    The properties that you change in a state are highlighted with blue color.
    In the code editor, you can see the changes recorded as changes to the base
    state.

    To keep the QML code clean, you should create a base state that contains all
    the types you will need in the application. You can then create states,
    in which you hide and show a set of items and modify their properties.
    This allows you to:

    \list

        \li Align items on different screens with each other.

        \li Avoid excessive property changes. If an item is invisible in the
            base state, you must define all changes to its child types as
            property changes, which leads to complicated QML code.

        \li Minimize the differences between the base state and the other states
            to keep the QML code short and readable and to improve performance.

        \li Avoid problems when using transitions and animation when changing
            states.

    \endlist

    To create screens for an application by using states:

    \list 1

        \li In the base state, add all items you will need in the
            application (1).
            While you work on one screen, you can click the
            \inlineimage qmldesigner-show-hide-icon.png
            icon to hide items on the canvas that are not part of a screen.

        \li In the \gui States pane, click the empty slot to create a new state
            and give it a name. For example, \c Normal.

        \li In the \gui Properties pane (2), deselect the \gui Visibility check box
            or set \gui Opacity to 0 for each item that is not needed in this
            view. If you specify the setting for the parent item, all child
            items inherit it and are also hidden.

            \image qmldesigner-screen-design.png "Designing screens"

        \li Create additional states for each screen and set the visibility
            or opacity of the items in the screen.

        \li To determine which view opens when the application starts, use the
            code editor to set the state of the root item of the .qml file, as
            specified by the following code snippet:

            \qml
            Item {
                state: "Normal"
            }
            \endqml

        \endlist

    \section1 Animating Screens

    To make movement between states smooth, you can specify transitions. You can
    use different types of animated transitions. For example, you can animate
    changes to property values and colors. You can use rotation animation to
    control the direction of rotation. For more information, see
    \l{Animation and Transitions in Qt Quick}.

    You can use the \c ParallelAnimation type to start several animations at
    the same time. Or use the \c SequentialAnimation type to run them one
    after another.

    You can use the code editor to specify transitions. For more information,
    see \l{Transition}.

    \section1 Adding User Interaction Methods

    You can use the following QML types to add basic interaction methods to
    screens:

    \list

        \li \l{Flickable}
            items can be flicked horizontally or vertically.

        \li FocusScope
            assists in keyboard focus handling when building reusable QML
            components.

        \li MouseArea enables simple mouse handling.

    \endlist

    From Qt 5.1, you can also use the following
    \l{Qt Quick Controls} to present or receive input from the user:

    \list

        \li \l{Button} provides a push button that you can associate with an
            action.

        \li CheckBox provides an option button that can be toggled on
            (checked) or off (unchecked).

        \li ComboBox provides a drop-down list. Add items to the combo box by
            assigning it a ListModel, or a list of strings to the model
            property.

        \li GroupBox provides a frame, a title on top, and place for various
            other controls inside the frame.

        \li \l{Label} provides a text label that follows the font and color scheme
            of the system.

        \li ProgressBar indicates the progress of an operation.

        \li RadioButton provides an option button that can be switched on
            (checked) or off (unchecked).

        \li \l{Slider}
            {Slider (Horizontal) and Slider (Vertical)} enable the user to move
            a slider handle along a horizontal or vertical groove and translate
            the handle's position into a value within the specified range.

        \li SpinBox enables the user to specify a value by clicking the up or
            down buttons, by pressing up or down on the keyboard, or by entering
            a value in the box.

        \omit
        Not visible in the item library in 3.2.
        \li StatusBar contains status information in your application. It
            does not provide a layout of its own, but requires you to position
            its contents, for instance by creating a \gui {Row Layout}.
        \endomit

        \li TextArea displays multiple lines of editable formatted text.

        \li TextField displays a single line of editable plain text.

        \omit
        Not visible in the item library in 3.2.
        \li ToolBar provides styling for ToolButton as well as other controls
            that it can contain. However, it does not provide a layout of its
            own, but requires you to position its contents, for instance by
            creating a \gui {Row Layout}.
        \endomit

        \li ToolButton provides a button that is functionally similar to
            \gui Button, but that looks more suitable on a \gui {Tool Bar}.

    \endlist


    \section1 Implementing Application Logic

    A user interface is only a part of an application, and not really useful by itself.
    You can use Qt or JavaScript to implement the application logic. For more information on
    using JavaScript, see \l{Integrating QML and JavaScript}.

    For an example of how to use JavaScript to develop a game, see the
    \l{QML Advanced Tutorial}.

*/