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/*!
    \page gettingstartedqml.html
    \title Getting Started Programming with QML
    \ingroup gettingStarted

    Welcome to the world of QML, the declarative UI language. In this Getting
    Started guide, we will create a simple text editor application using QML.
    After reading this guide, you should be ready to develop your own applications
    using QML and Qt C++.

    \section1 Installation

    First, we would need to install the latest version of Qt that includes \l{Qt
    Quick}, which is Qt 4.7. The \l{Installation} {installation} guide contains
    installation instructions and requirements for different platforms.

    Qt Quick includes a declarative language called
    \l{Introduction to the QML language}{QML}, the \l{Qt Declarative Module}, and
    \l{QML Viewer}.

    \section1 QML to Build User Interfaces

    The application we are building is a simple text editor that will load, save,
    and perform some text manipulation. This guide will consist of two parts. The
    first part will involve designing the application layout and behaviors using
    declarative language in QML. For the second part, file loading and saving will
    be implemented using Qt C++. Using
    \l {The Meta-Object System}{Qt's Meta-Object System}, we can expose C++ functions
    as properties that QML elements can use. Utilizing QML and Qt C++, we can
    efficiently decouple the interface logic from the application logic.

    \image qml-texteditor5_editmenu.png

    The final source code is in the \c{examples/tutorials/gettingStarted/gsQml}
    directory. You may need to compile the C++ plugin in the
    \c{examples/tutorials/gettingStarted/gsQml/} first. This will put the
    C++ plugin in a directory where the QML files may find it.

    To launch the text editor, merely provide the included \l{QML Viewer}{qmlviewer}
    tool with the QML file as the argument. The C++ portion of this tutorial assumes
    that the reader possesses basic knowledge of Qt's compilation procedures.

    Tutorial chapters:
    \list 1
        \o \l {Defining a Button and a Menu}{Defining a Button and a Menu}
        \o \l {Implementing a Menu Bar}{Implementing a Menu Bar}
        \o \l {Building a Text Editor}{Building a Text Editor}
        \o \l {Decorating the Text Editor}{Decorating the Text Editor}
        \o \l {Extending QML using Qt C++}{Extending QML using Qt C++}
    \endlist

    \section1 Defining a Button and a Menu

    \section2 Basic Component - a Button

    We start our text editor by building a button. Functionally, a button has a mouse
    sensitive area and a label. Buttons perform actions when a user presses the button.

    In QML, the basic visual item is the \l {Rectangle}{Rectangle} element. The
    \c Rectangle element has properties to control the element's appearance and location.

    \snippet examples/tutorials/gettingStarted/gsQml/parts/part0/Button.qml document

    First, the \c { import QtQuick 1.0 } allows the qmlviewer tool to import the QML elements
    we will later use. This line must exist for every QML file. Notice that the version
    of Qt modules is included in the import statement.

    This simple rectangle has a unique identifier, \c simplebutton, which is bound to the
    id property. The \c Rectangle element's properties are bound to values by listing the
    property, followed by a colon, then the value. In the code sample, the color \c grey
    is bound to the the Rectangle's \c color property. Similarly, we bind the \c width
    and \c height of the Rectangle.

    The \l {Text}{Text} element is a non-editable text field. We name this \c Text element
    \c buttonLabel. To set the string content of the Text field, we bind a value to the
    \c text property. The label is contained within the Rectangle and in order to center
    it in the middle, we assign the \c anchors of the Text element to its parent, which
    is called \c simplebutton. Anchors may bind to other items' anchors, allowing layout
    assignments simpler.

    We shall save this code as \c SimpleButton.qml. Running qmlviewer with the file as the
    argument will display the grey rectangle with a text label.

    \image qml-texteditor1_simplebutton.png

    To implement the button click functionality, we can use QML's event handling. QML's event
    handling is very similar to \l {Signals & Slots}{Qt's signal and slot} mechanism. Signals
    are emitted and the connected slot is called.

    \code
        Rectangle{
            id:simplebutton
            ...

            MouseArea{
                id: buttonMouseArea

                anchors.fill: parent //anchor all sides of the mouse area to the rectangle's anchors
                        //onClicked handles valid mouse button clicks
                onClicked: console.log(buttonLabel.text + " clicked" )
            }
        }
    \endcode

    We include a \l{MouseArea} element in our simplebutton. \c MouseArea elements describe
    the interactive area where mouse movements are detected. For our button, we anchor the
    whole MouseArea to its parent, which is \c simplebutton. The \c anchors.fill syntax is
    one way of accessing a specific property called \c fill inside a group of properties
    called \c anchors. QML uses \l {Anchor-based Layout in QML}{anchor based layouts} where
    items can anchor to another item, creating robust layouts.

    The \c MouseArea has many signal handlers that are called during mouse movements within
    the specified \c MouseArea boundaries. One of them is \c onClicked and it is called
    whenever the acceptable mouse button is clicked, the left click being the default. We
    can bind actions to the onClicked handler. In our example, \c console.log() outputs text
    whenever the mouse area is clicked. The function \c console.log() is a useful tool for
    debugging purposes and for outputting text.

    The code in \c SimpleButton.qml is sufficient to display a button on the screen and
    output text whenever it is clicked with a mouse.

    \code
        Rectangle {
            id: button
            ...

            property color buttonColor: "lightblue"
            property color onHoverColor: "gold"
            property color borderColor: "white"

            signal buttonClick()
            onButtonClick: {
                console.log(buttonLabel.text + " clicked" )
            }

            MouseArea{
                onClicked: buttonClick()
                hoverEnabled: true
                onEntered: parent.border.color = onHoverColor
                onExited:  parent.border.color = borderColor
            }

            //determines the color of the button by using the conditional operator
            color: buttonMouseArea.pressed ? Qt.darker(buttonColor, 1.5) : buttonColor
        }
    \endcode

    A fully functioning button is in \c Button.qml. The code snippets in this article
    have some code omitted, denoted by ellipses because they were either introduced
    earlier in the previous sections or irrelevant to the current code discussion.

    Custom properties are declared using the \c {property type name} syntax. In the
    code, the property \c buttonColor, of type \c color, is declared and bound to
    the value \c{"lightblue"}. The \c buttonColor is later used in a conditional
    operation to determine the buttons's fill color. Note that property value
    assignment is possible using the \c= equals sign, in addition to value binding
    using the \c : colon character. Custom properties allow internal items to be
    accessible outside of the Rectangle's scope. There are basic
    \l{QML Basic Types}{QML types} such as \c int, \c string, \c real, as well as
    a type called \c variant.

    By binding the \c onEntered and \c onExited signal handlers to colors, the
    button's border will turn yellow when the mouse hovers above the button and
    reverts the color when the mouse exits the mouse area.

    A \c buttonClick() signal is declared in \c Button.qml by placing the \c signal
    keyword in front of the signal name. All signals have their handlers automatically
    created, their names starting with \c on. As a result, the \c onButtonClick is
    \c buttonClick's handler. The \c onButtonClick is then assigned an action to
    perform. In our button example, the \c onClicked mouse handler will simply call
    \c onButtonClick, which displays a text. The \c onButtonClick enables outside
    objects to access the \c {Button}'s mouse area easily. For example, items may
    have more than one \c MouseArea declarations and a \c buttonClick signal can
    make the distinction between the several \c MouseArea signal handlers better.

    We now have the basic knowledge to implement items in QML that can handle
    basic mouse movements. We created a \c Text label inside a \c Rectangle,
    customized its properties, and implemented behaviors that respond to mouse
    movements. This idea of creating elements within elements is repeated
    throughout the text editor application.

    This button is not useful unless used as a component to perform an action.
    In the next section, we will soon create a menu containing several of these
    buttons.

    \image qml-texteditor1_button.png

    \section2 Creating a Menu Page

    Up to this stage, we covered how to create elements and assign behaviors inside
    a single QML file. In this section, we will cover how to import QML elements and how
    to reuse some of the created components to build other components.

    Menus display the contents of a list, each item having the ability to perform an action.
    In QML, we can create a menu in several ways. First, we will create a menu containing
    buttons which will eventually perform different actions. The menu code is in
    \c FileMenu.qml.

    \code
        import QtQuick 1.0                \\import the main Qt QML module
        import "folderName"            \\import the contents of the folder
        import "script.js" as Script        \\import a Javascript file and name it as Script
    \endcode

    The syntax shown above shows how to use the \c import keyword. This is required to
    use JavaScript files, or QML files that are not within the same directory. Since
    \c Button.qml is in the same directory as \c FileMenu.qml, we do not need to import
    the \c Button.qml file to use it. We can directly create a \c Button element by declaring
    \c Button{}, similar to a \c Rectangle{} declaration.

    \code
    In FileMenu.qml:

        Row{
            anchors.centerIn: parent
            spacing: parent.width/6

            Button{
                id: loadButton
                buttonColor: "lightgrey"
                label: "Load"
            }
            Button{
                buttonColor: "grey"
                id: saveButton
                label: "Save"
            }
            Button{
                id: exitButton
                label: "Exit"
                buttonColor: "darkgrey"

                onButtonClick: Qt.quit()
            }
        }
    \endcode

    In \c FileMenu.qml, we declare three \c Button elements. They are declared
    inside a \l {Row}{Row} element, a positioner that will position its children
    along a vertical row. The \c Button declaration resides in Button.qml,
    which is the same as the \c Button.qml we used in the previous section.
    New property bindings can be declared within the newly created buttons,
    effectively overwriting the properties set in \c Button.qml. The button
    called \c exitButton will quit and close the window when it is clicked.
    Note that the signal handler \c onButtonClick in \c Button.qml will be
    called in addition to the \c onButtonClick handler in \c exitButton.

    \image qml-texteditor1_filemenu.png

    The \c Row declaration is declared in a \c Rectangle, creating a rectangle
    container for the row of buttons. This additional rectangle creates an indirect
    way of organizing the row of buttons inside a menu.

    The declaration of the edit menu is very similar at this stage. The menu has
    buttons that have the labels: \c Copy, \c Paste, and \c {Select All}.

    \image qml-texteditor1_editmenu.png

    Armed with our knowledge of importing and customizing previously made
    components, we may now combine these menu pages to create a menu bar,
    consisting of buttons to select the menu, and look at how we may structure
    data using QML.

    \section1 Implementing a Menu Bar

    Our text editor application will need a way to display menus using a menu bar.
    The menu bar will switch the different menus and the user can choose which menu
    to display. Menu switching implies that the menus need more structure than
    merely displaying them in a row. QML uses models and views to structure data
    and display the structured data.

    \section2  Using Data Models and Views

    QML has different \l{QML Data Models}{data views} that display
    \l{QML Data Models}{data models}. Our menu bar will display the menus in a list,
    with a header that displays a row of menu names. The list of menus are declared
    inside a \c VisualItemModel. The \l{VisualItemModel}{\c VisualItemModel}
    element contains items that already have views such as \c Rectangle elements
    and imported UI elements. Other model types such as the \l{ListModel}{\c ListModel}
    element need a delegate to display their data.

    We declare two visual items in the \c menuListModel, the \c FileMenu and the
    \c EditMenu. We customize the two menus and display them using a
    \l {ListView}{ListView}. The \c MenuBar.qml file contains the QML declarations
    and a simple edit menu is defined in \c EditMenu.qml.

    \code
        VisualItemModel{
            id: menuListModel
            FileMenu{
                width: menuListView.width
                height: menuBar.height
                color: fileColor
            }
            EditMenu{
                color: editColor
                width:  menuListView.width
                height: menuBar.height
            }
        }
    \endcode

    The \l {ListView}{ListView} element will display a model according to a delegate.
    The delegate may declare the model items to display in a \c Row element or display
    the items in a grid. Our \c menuListModel already has visible items, therefore,
    we do not need to declare a delegate.

    \code
        ListView{
            id: menuListView

            //Anchors are set to react to window anchors
            anchors.fill:parent
            anchors.bottom: parent.bottom
            width:parent.width
            height: parent.height

            //the model contains the data
            model: menuListModel

            //control the movement of the menu switching
            snapMode: ListView.SnapOneItem
            orientation: ListView.Horizontal
            boundsBehavior: Flickable.StopAtBounds
            flickDeceleration: 5000
            highlightFollowsCurrentItem: true
            highlightMoveDuration:240
            highlightRangeMode: ListView.StrictlyEnforceRange
        }
    \endcode

    Additionally, \c ListView inherits from \l{Flickable}{\c Flickable}, making
    the list respond to mouse drags and other gestures. The last portion of the
    code above sets \c Flickable properties to create the desired flicking movement
    to our view. In particular,the property \c highlightMoveDuration changes the
    duration of the flick transition. A higher \c highlightMoveDuration value
    results in slower menu switching.

    The \c ListView maintains the model items through an \c index and each visual
    item in the model is accessible through the \c index, in the order of the
    declaration. Changing the \c currentIndex effectively changes the highlighted
    item in the \c ListView. The header of our menu bar exemplify this effect.
    There are two buttons in a row, both changing the current menu when clicked.
    The \c fileButton changes the current menu to the file menu when clicked,
    the \c index being \c 0 because \c FileMenu is declared first in the
    \c menuListModel. Similarly, the \c editButton will change the current
    menu to the \c EditMenu when clicked.

    The \c labelList rectangle has \c z value of \c 1, denoting that it is displayed
    at the front of the menu bar. Items with higher \c z values are displayed in front
    of items with lower \c z values. The default \c z value is \c 0.

    \code
        Rectangle{
            id: labelList
            ...
            z: 1
            Row{
                anchors.centerIn: parent
                spacing:40
                Button{
                    label: "File"
                    id: fileButton
                    ...
                    onButtonClick: menuListView.currentIndex = 0
                }
                Button{
                    id: editButton
                    label: "Edit"
                    ...
                    onButtonClick:    menuListView.currentIndex = 1
                }
            }
        }
    \endcode

    The menu bar we just created can be flicked to access the menus or by clicking
    on the menu names at the top. Switching menu screens feel intuitive and responsive.

    \image qml-texteditor2_menubar.png

    \section1 Building a Text Editor

    \section2 Declaring a TextArea

    Our text editor is not a text editor if it didn't contain an editable text area.
    QML's \l {TextEdit}{TextEdit} element allows the declaration of a multi-line
    editable text area. \l {TextEdit}{TextEdit} is different from a \l {Text}{Text}
    element, which doesn't allow the user to directly edit the text.

    \code
        TextEdit{
            id: textEditor
            anchors.fill:parent
            width:parent.width; height:parent.height
            color:"midnightblue"
            focus: true

            wrapMode: TextEdit.Wrap

            onCursorRectangleChanged: flickArea.ensureVisible(cursorRectangle)
        }
    \endcode

    The editor has its font color property set and set to wrap the text. The
    \c TextEdit area is inside a flickable area that will scroll the text if the
    text cursor is outside the visible area. The function \c ensureVisible() will
    check if the cursor rectangle is outside the visible boundaries and move the
    text area accordingly. QML uses Javascript syntax for its scripts, and as previously
    mentioned, Javascript files can be imported and used within a QML file.

    \code
        function ensureVisible(r){
            if (contentX >= r.x)
                contentX = r.x;
            else if (contentX+width <= r.x+r.width)
                contentX = r.x+r.width-width;
            if (contentY >= r.y)
                contentY = r.y;
            else if (contentY+height <= r.y+r.height)
                contentY = r.y+r.height-height;
        }
    \endcode

    \section2 Combining Components for the Text Editor

    We are now ready to create the layout of our text editor using QML. The text
    editor has two components, the menu bar we created and the text area. QML allows
    us to reuse components, therefore making our code simpler, by importing components
    and customizing when necessary. Our text editor splits the window into two;
    one-third of the screen is dedicated to the menu bar and two-thirds of the screen
    displays the text area. The menu bar is displayed in front of any other elements.

    \code
        Rectangle{

            id: screen
            width: 1000; height: 1000

            //the screen is partitioned into the MenuBar and TextArea. 1/3 of the screen is assigned to the MenuBar
            property int partition: height/3

            MenuBar{
                id:menuBar
                height: partition
                width:parent.width
                z: 1
            }

            TextArea{
                id:textArea
                anchors.bottom:parent.bottom
                y: partition
                color: "white"
                height: partition*2
                width:parent.width
            }
        }
    \endcode

    By importing reusable components, our \c TextEditor code looks much simpler.
    We can then customize the main application, without worrying about properties
    that already have defined behaviors. Using this approach, application layouts
    and UI components can be created easily.

    \image qml-texteditor3_texteditor.png

    \section1 Decorating the Text Editor
    \section2 Implementing a Drawer Interface

    Our text editor looks simple and we need to decorate it. Using QML, we can declare
    transitions and animate our text editor. Our menu bar is occupying one-third of the
    screen and it would be nice to have it only appear when we want it.