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/*!
    \page tutorials-declarative-contacts.html
    \startpage {index.html}{Qt Reference Documentation}
    \nextpage {tutorials/declarative/contacts/part1}{Chapter 1}

    \title Declarative UI Tutorial
    \ingroup howto
    \ingroup tutorials
    \brief An introduction to using Qt Declarative UI to put together a
    simple animated application.

    \omit
    At the time of writing the tutorial Declarative UI was still under
    development.  It is extremely likely that an update will be required
    prior to 4.6 release.
    \endomit

    This tutorial gives an introduction to using the Qt Declarative UI
    animation framework.

    In this process we will learn about some of the basics of using
    Declarative UI, such as

    \list
    \o Basic drawing
    \o States and Transitions
    \o Reuse of components
    \o Models and Views
    \endlist

    An existing knowledge of Qt is not required.

    The tutorial's source code is located in Qt's
    \c examples/declarative/tutorials/contacts directory.
    It is split up into a number of sub directories, and within each
    sub directory the files are numbered in an order of increasing features.

    The code in this example is not compiled, but interpreted at run time.
    This means you should use the qmlviewer application provided with
    Qt to run the examples.

    \list
    \o \l{tutorials/declarative/contacts/part1}{Drawing and Animation}
    \o \l{tutorials/declarative/contacts/part2}{Reusing QML Components}
    \o \l{tutorials/declarative/contacts/part3}{Models, Views and Delegates}
    \endlist
*/

/*!
    \page tutorials-declarative-contacts-part1.html
    \contentspage {Declarative UI Tutorial}{Contents}
    \nextpage {tutorials/declarative/contacts/part2}{Chapter 2}
    \example tutorials/declarative/contacts/part1
    \title Drawing and Animation
    \tableofcontents

    The first part of this tutorial covers basic drawing of elements on the
    screen and causing them to animate.

    \section1 Drawing

    In this first chapter we will build a button that indicates something
    can be removed and asks for confirmation.  When clicked it will expand
    from a small button with a trash can icon, to a wide button with a
    confirm icon on the left, the text "Remove" in the middle, and a
    cancel icon on the right.

    \image declarative-removebutton.gif

    Because Declarative UI is declarative, you don't pass instructions on
    what to paint in a sequential manner as you may be used to.  Instead
    elements and how they appear on the screen are declared in much the
    same was as elements on a web page are declared.  This is done using
    the Qt Markup Language which we will refer to by the abbreviation QML
    for the remainder of the tutorial.

    We will start by drawing a simple red rectangle with rounded corners.

    \image declarative-roundrect.png

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/1/RemoveButton.qml 0

    This is one of the simplest of QML components.  It describes a rectangle with
    some simple properties.  In QML all components start with a capital
    letter, and their properties with lower case letters.

    Apart from the properties all QML components share, the \l{Rectangle}{Rectangle} component has the properties

    \list
    \o color - The background color of the rectangle
    \o tintColor - The overlay color of the rectangle
    \o gradientColor - The color at the base of the rectangle to blend upwards
    \o pen - The description of how to draw the border of the rectangle
    \o radius - The corner radius used to draw rounded rectangles.
    \endlist

    There are also a number of properties all QML components shares, described
    in the \l{Item}{Item} element reference documentation.  The rectangle drawn in the
    above code uses the properties;

    \list
    \o id - An identifier of the component
    \o width - the width of the component when drawn
    \o height - the height of the component when drawn
    \endlist

    Currently we have described a rectangle with a width and height of 30 pixels, filled in with
    the color red and with rounded corners using a radius of 5.

    \section1 Layout

    The next step of the tutorial adds an image over the rectangle.  We
    will do this by adding an \l{Image}{Image} component as a child of the
    \l{Rectangle}{Rectangle} component.  All QML components have a list of children which
    are drawn in order after the parent component has been drawn.
    By having the \l{Image}{Image}
    component as a child of the \l{Rectangle}{Rectangle} component we ensure it is drawn
    over the \l{Rectangle}{Rectangle} component.  Children also are affected by the opacity
    of the parent component and calculate their position in within the bounds of
    the parent component.

    \image declarative-removebutton-close.png

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/2/RemoveButton.qml 0

    The trashIcon image is added as a child of the Rectangle.  In this case
    the children property isn't explicitly used because the default property
    of the \l{Rectangle}{Rectangle} component is its children.  Some elements often don't have children
    and use some other default component.  When this is the case its possible
    to explicitly list the sub component as a child as follows:

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/2a/RemoveButton.qml 0

    The \l{Image}{Image} element allows loading an image file for display.  The source
    specified is a URL, and in this case refers to a portable network graphics
    file in a relative directory to where the QML file was loaded from.

    Also new in this code is the use of anchors.  In QML components can either
    have their position and size specified explicitly using x, y, width
    and height, or they can instead specify the size and position in relation
    to either parent or sibling elements.  The \l{Image}{Image} component uses
    a combination of both styles.  It has a fixed size, but specifies its
    position to align to the right of its parent and for its vertical center
    to align with the vertical center of its parent.  Setting a property
    by the identifier of a separate property binds them.  This means
    that if while running the example the position of the \l{Rectangle}{Rectangle} component's
    vertical center changed, so to would the vertical center of
    the \l{Image}{Image} component.

    The parent value is a special identifier that always refers to the
    parent component of a component.

    Anchors are most useful when the size of items might change based on
    the component state or contents.  However they are limited in that they
    must always refer to a parent or sibling component.  See
    \l{anchor-layout}{Anchor-based Layout} for more information on using
    anchors in QML.

    At this point the initial state of the RemoveButton is complete.  A small
    rounded rectangle with a trash icon.  Next we will design the open
    state for the button.

    \image declarative-removebutton-open.png

    This is a wider rectangle with two images and some text.  The code to
    draw this state of the button could be written as follows:

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/3/RemoveButton.qml 0

    The rectangle width is now wider by 200 pixels.  Also the trashIcon has
    been replaced.  Normally we wouldn't
    remove the trashIcon when developing an alternate state of the RemoveButton,
    however since this is a tutorial its been done so that its easier to
    understand the alternate state we are aiming for and how it relates to
    transitioning between states.

    We also introduce the \l{Text}{Text} element.
    Left and Right anchors are specified in terms of the neighboring icons
    because we want text to fill the space between the icons.  This
    means as the parent removeButton gets wider, so will the text component.
    It also means that if we animate a width change on the removeButton,
    any bindings, that is the values specified by an expression such as
    \c{parent.left} will be evaluated and animated as well.

    \section1 Defining States

    When designing a component with multiple states, it should be developed
    in the initial state and the changes that would be made specified
    as an additional state.  Its not normally possible to add new children
    to an element when changing state
    This means that all possible child components should be included
    in the initial state, and those that should not be visible in the initial
    state should have their opacity set to zero.  Thus
    for the RemoveButton we specify the starting size of the RemoveButton
    and hide any items that should not initially be visible.

    The code snippet below shows what the start of the duel state specification
    might look like.

    \code
    Rectangle {
        id: removeButton
        width: 30
        height: 30
        color: "red"
        radius: 5
        Image {
            id: trashIcon
            width: 22
            height: 22
            anchors.right: parent.right
            anchors.rightMargin: 4
            anchors.verticalCenter: parent.verticalCenter
            src: "../../shared/pics/trash.png"
            opacity: 1
        }
        Image {
            id: cancelIcon
            width: 22
            height: 22
            anchors.right: parent.right
            anchors.rightMargin: 4
            anchors.verticalCenter: parent.verticalCenter
            src: "../../shared/pics/cancel.png"
            opacity: 0
        }
    \endcode

    The code above includes components from both states of the RemoveButton,
    but by setting opacity="0" for the cancelIcon it means that the
    components of the second state won't be drawn yet.
    The base state of a component always has an empty name, however new
    states can be added that describe how a component and its children
    should be changed.  For the RemoveButton there is only one non-base state
    required.  In this tutorial we will name it the 'opened' state.

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/4/RemoveButton.qml states

    In the opened state the width of the button itself changes from the base
    width of 30 to the new width of 230.  Also the opacity of the children
    are changed so that the trash icon is now hidden and the other elements
    are now visible.

    \section1 Changing States

    To trigger the change we will react to the 'clicked' signal of a
    MouseRegion component.

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/4/RemoveButton.qml mouse region

    MouseRegion components handle mouse actions within their geometry.  This
    geometry behaves the same way as painted components, such that children
    cover their parents and later siblings will cover earlier siblings and
    all the children of the earlier sibling, should they overlap.

    When a component has a signal, such as clicked, the action for the signal
    can be specified using \c{onSignalName}, as is done above.  In this
    case when the clicked signal is emitted by the MouseRegion component,
    a function called \c{toggle()} is called.  It might also have been written

    \code
    onClicked: { removeButton.state='opened' }
    \endcode

    However in this case we are using a function because it allows multiple
    mouse regions to use the same functionality, and also makes it
    easier to specify complex behavior in response to a signal.

    An alternative would be to explicitly state the connection:

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/4a/RemoveButton.qml mouse region

    This will connect to the \c{clicked()} signal of the trashMouseRegion component
    and execute the associated script.

    The \c{toggle()} function is a new function specified as part of the remove
    button element.

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/4/RemoveButton.qml script

    Any QML component can have a set of resources specified.  One of those
    resources is any Script that might be needed.   See the
    \l{QtScript Module} for more information on how to write
    script code in Qt.

    It is possible to refer to identified QML components
    within the script.  Hence the function for our RemoveButton will check
    if the state is already open to determine what the new state should be.

    \section1 Animation

    Currently the RemoveButton is functional, but snaps between our two states.
    Fortunately making the transition between states smooth is very simple.
    We only need one more bit of code at the end of our removeButton component.

    \snippet declarative/tutorials/contacts/1_Drawing_and_Animation/5/RemoveButton.qml transition

    All QML components have a transitions property.  This describes how
    properties of items within the component should change.  In this case
    we specify that if the x, width or opacity of the removeButton or its
    children change due to a change in state, that they should take 200ms
    to complete their transition.

    \omit
        TODO More on types of animation, e.g. ColorAnimation, Behaviors.
    \endomit

    In the next chapter we will show how we can use the remove button in
    other QML components.
*/

/*!
    \page tutorials-declarative-contacts-part2.html
    \contentspage {Declarative UI Tutorial}{Contents}
    \previouspage {tutorials/declarative/contacts/part1}{Chapter 1}
    \nextpage {tutorials/declarative/contacts/part3}{Chapter 3}
    \example tutorials/declarative/contacts/part2
    \title Reusing QML Components
    \tableofcontents

    The second part of this tutorial covers how to reuse QML components and
    have them interact with each other.  The RemoveButton developed in the
    previous chapter is intended to be part of a more complex control for
    editing a field of our contact.  This ContactField in turn is intended
    to be used in a contact editing control.

    \image declarative-reuse-3.png

    \section1 Loading QML Components

    Reusing the RemoveButton itself is very simple.  When parsing a QML file
    if a Component is referred to that isn't already in the system, Qt
    will try to load it from a file of the same name with the ".qml" extension.

    \snippet declarative/tutorials/contacts/2_Reuse/1/ContactField.qml load

    The above QML code will attempt to load the RemoveButton component from
    a file with the name "RemoveButton.qml" from the following search paths.

    \list
    \o Any imported directories. These are listed at the start of the file using
        \c { import "path" }.
    \o the directory of the QML code file
    \endlist

    All the properties of the button are
    accessible and can be overridden from defaults.  The loaded component
    can also refer to elements further up in the tree, so that code within
    RemoveButton.qml could refer to the contactField component.
    Only properties of the top level element in RemoveButton.qml are visible to
    the contact field.

    There are also two other ways to reuse components in QML.  A component
    can be reused from within the same QML file using Component and ComponentInstance
    elements.  The next code snippet produces three red rounded rectangles
    within a large blue rectangle.

    \image declarative-reuse-bluerect.png

    \snippet declarative/tutorials/contacts/2_Reuse/1b/BlueRect.qml all

    This can be useful when the component is not complex enough to justify its
    own file.  The third way to reuse components allows for delaying loading
    of the QML until some later event.  \l{Loader}{Loader} includes
    a special child, item, which has its definition provided by the
    contents of the source property of the loader.

    \snippet declarative/tutorials/contacts/2_Reuse/1a/ContactField.qml load

    This last method is useful if the contents of a item need to change at
    run time or if the initial complexity of the loaded QML needs to be
    reduced in order to improve the time it takes to start the application. In
    chapter three this method is used to improve performance of
    scrolling through very large numbers of items.

    Because of its simplicity, the first method is the recommended in most
    cases and will be the focus of the remainder of this chapter.

    \section1 Properties and Signals

    The next task is to be able to control aspects of the RemoveButton from
    the components that use it.  In particular controlling how far it
    expands and how it reacts when the user clicks on the confirm icon
    of the remove button.  When reusing a component in a separate QML file
    only the attributes of the root element are visible.  To allow controlling
    attributes of child elements within an imported component we need to define
    some properties and signals for the RemoveButton.

    \snippet declarative/tutorials/contacts/2_Reuse/2/RemoveButton.qml define properties and signals

    The children of the remove button can use these properties and signals.  The
    opened state can now bind the expanded width to the expandedWidth property.

    \snippet declarative/tutorials/contacts/2_Reuse/2/RemoveButton.qml use width

    Also when the confirm icon is clicked, as well as toggling the state it will
    emit the confirmed signal of the RemoveButton component.

    \snippet declarative/tutorials/contacts/2_Reuse/2/RemoveButton.qml use signal

    These properties and signals can also be accessed from the contact field the same
    way standard system component properties and signals are accessed.

    \snippet declarative/tutorials/contacts/2_Reuse/2/ContactField.qml use properties and signals

    Now when the remove button is expanded, it will expand to the width of the
    contact field.  Also when the user confirms the remove action, the
    text section of the contact field will be cleared.

    \section1 States

    Its also possible to access the state of included components.  The FieldText
    component we will use in this tutorial is also been written specifically
    for our contacts application.  In
    this case we want it to expand when editing.  One way to do this would
    be to anchor the field text component to the center of its parent and
    then let its own width change push the remove button away, however that
    would make it difficult to have the remove button also push the field
    text to the left when the remove button expands.  Instead we will anchor
    the right edge of the field text to the left edge of the remove button
    and use a state change in the contact field itself to move the
    remove button and the field icon out of
    view.

    \snippet declarative/tutorials/contacts/2_Reuse/3/ContactField.qml all

    Apart from accessing the fieldText.state, the above code also uses the when
    attribute of its own editingText state.  This is an alternative to using
    a signal to change state.  When the value of the expression for the
    when attribute changes, Qt will detect if the contactField needs to enter
    that state.  In the FieldText element a similar approach is used to fade
    out the label of the FieldText when the user enters some text of their own.

    \snippet declarative/tutorials/contacts/2_Reuse/3/FieldText.qml behavior

    \c{fieldText} is the enclosing component and \c{textEdit} is a TextEdit element
    provided by Qt.  In the QML code above, the opacity of the textLabel is
    only 1 if the text for the textEdit is empty.  This is a form of
    short cut to using states for an element, useful if only one property
    is changing as it is for the textLabel.  To animate a property change is
    similar to animating a state change.  Using the Behavior element we can
    specify how the property changes if it does change state, allowing for
    a smooth transition.

    \section1 Key and Mouse Focus

    Setting focus to true on a component does not always mean
    that the component has focus.  This is due to the declarative nature
    of QML, and can be affected by multiple components both indicating
    focus to be true.  At the time of writing this tutorial both key and mouse
    focus handling are still being improved.  Hence we will only lightly cover
    the topic.

    For an item to have key focus in QML it is required that:

    \list
    \o If there is a FocusScope ancestor of the component that it has focus as well.
    \o That it is the most recent component within the focus realms descendent's
        to receive focus
    \endlist

    The read-only property activeFocus can be used to determine whether a
    component will receive key input.  Any un-handled keys will be passed to
    the components parent, which in turn will pass keys it doesn't handle up to its
    own ancestors.

    Some components such as ListView components are also FocusScope components, as they
    handle focus among the child list items.

    At this stage of the tutorial it is sufficient to use the setting of 'focus'
    as we only have a list of line edits and only one should be active at any given time.

    Currently if multiple contact fields were put into our contact editor,
    any of the FieldText components could be clicked and opened, and
    any of the RemoveButton components could be clicked and opened, all
    at the same time.  This leads to situations where the users actions
    are ambiguous

    \image declarative-reuse-focus.png

    To counteract this we will add a property of the root element to indicate
    when an element has 'grabbed' mouse interaction, preventing other
    clickable elements from reacting.

    \snippet declarative/tutorials/contacts/2_Reuse/4/Contact.qml grab property

    The code that we want to disable then simply needs to check this property before
    acting.

    \snippet declarative/tutorials/contacts/2_Reuse/4/RemoveButton.qml grab

    \note Handling Key and Mouse focus in QML is quite likely to change before
    the Qt 4.6 release.
*/

/*!
    \page tutorials-declarative-contacts-part3.html
    \contentspage {Declarative UI Tutorial}{Contents}
    \previouspage {tutorials/declarative/contacts/part2}{Chapter 2}
    \example tutorials/declarative/contacts/part3
    \title Models, Views and Delegates
    \tableofcontents

    In the previous chapters we designed a component to display and
    edit a contact.  The next step is to display a list of those contacts
    and allow the user to expand individual contacts for editing.

    As the previous elements will not be changed in this section, they have
    been moved to a lib directory for this tutorial and the relevant
    import path has been used.

    \section1 Simple List View

    Displaying lists requires three components.  A model that holds the
    data displayed, a delegate to indicate how elements are drawn and
    a view to arrange the elements.

    \image declarative-tutorial-list.gif

    For the purposes of this tutorial we will be using an SQL query as our
    data model.  This can be declared in the resources section of
    the parent item.

    \snippet declarative/tutorials/contacts/3_Collections/1/ContactView.qml model

    The SqlConnection component describes how to connect to the database in
    much the same ways as the QSqlDatabase::addDatabase() function is used.
    In this case an SQLite database is used as it can be connected to as a
    file, reducing complexity in setting up a database server or credentials.

    The SqlQuery component allows various forms of queries to be described.
    When the query is a select statement, the component also acts as a model
    allowing it to provide data to a ListView component.  The query above
    retrieves the fields recid, label, email and phone from a contacts table,
    and orders the results by the label of the contact first, and then by
    the recid for any contacts with equivalent labels.

    The ListView component is suitable for displaying models and is declared
    much like any other QML component.  The ListView component also has
    a delegate property that defines how to construct components for items in the list.

    \snippet declarative/tutorials/contacts/3_Collections/1/ContactView.qml delegate

    Unlike a child element, this describes a template on how to build the component
    for each element, much in the same way that components are loaded from
    files such as RemoveButton.qml.  The are constructed or destroyed as items
    scroll into our out of the visible area of the list.

    The entire view component will look like:

    \snippet declarative/tutorials/contacts/3_Collections/1/ContactView.qml view

    This gives us a list of contacts that the user can flick through.

    \section1 Animating Delegates

    The next step is to allow the user to click on a contact to edit the
    contact.  We will take advantage of QML to open a Contact component
    in the list rather than as a new dialog or view.  This is very
    similar to how the contents of the FieldText and RemoveButton components
    are swapped in and out.

    \image declarative-tutorial-list-open.gif

    \snippet declarative/tutorials/contacts/3_Collections/2/ContactView.qml components

    The first step is to have two children of our delegate component that can
    be swapped between.  The plain Text component and the Contact component built
    in the previous chapters.  We also add a MouseRegion that can be clicked upon
    to change the state of the delegate component.

    \snippet declarative/tutorials/contacts/3_Collections/2/ContactView.qml states

    This defines the open state of the delegate.  It changes the height of the delegate
    component to that of the whole list view, pushing the other items off each end of
    the list.  It sets the listview's scroll viewportY of the ListView to the
    y value of the delegate so that the top of the delegate matches the top of the list view.
    The next step is to lock the list view.  This prevents the user being able to flick
    the list view. The final to properties that are set should
    be familiar from previous chapters, setting the opacity of the items such
    that the new item is visible and the old item hidden.

    We then add a transition so that this becomes animated:

    \snippet declarative/tutorials/contacts/3_Collections/2/ContactView.qml transitions

    This allows the user to click on an item to enter the open state.  Elsewhere on our
    contact view we add a button so that the user can leave the detailed view of the contact.

    \snippet declarative/tutorials/contacts/3_Collections/2/ContactView.qml button

    And connect it's clicked value to some script to set the state of the delegate
    back to its default state.

    \snippet declarative/tutorials/contacts/3_Collections/2/ContactView.qml connections

    Something worth noting at this point is that every delegate created has this connection.
    It is important to check whether the delegate is the one in the open state, and
    taking some effort to ensure only one is, before acting on the signal from the button.

    \section1 Performance Considerations

    We have now made a contact application that can view a list of contacts, open one,
    and close it again.  Its now time to take a moment and consider the implications
    of a list view delegate.  It is created for each and every item in the list,
    and while the list cleans up after itself and only has delegate components constructed
    for visible items and any single point of animation, the list can scroll very quickly.
    This means potentially thousands of delegate components will be constructed and
    destroyed when the user is flicking through the list.

    Its important then to try and minimize the complexity of the delegate.  This
    can be done by delaying the loading of the component.  By using the qml property
    of the \l{Item}{Item} component, we can delay building the Contact.qml item until the user
    attempts to open the list.

    \snippet declarative/tutorials/contacts/3_Collections/3/ContactView.qml setting qml

    \l{Loader}{Loader} has a source property that represents the filename for the contents of
    a special item child of the \l{Loader}{Loader}.  By setting the source property of the Details
    component on clicking the mouse region, the more complex component isn't loaded
    until needed.  The down side about this though is the properties of Contact
    cannot be set until the item is loaded.  This requires using the Bind element.


    \snippet declarative/tutorials/contacts/3_Collections/3/ContactView.qml binding

    Unlike binding a value to the property of a component directly, the Bind element
    allows both the target and the property set to themselves be to dynamic values.
    This means that when the source property is set, it will change the
    item property of the Details component.  This in turn triggers the Bind
    elements to set the required properties of the item, which is now
    an instance of the Contact component.
*/