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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 qtqml-syntax-objectattributes.html \title QML Object Attributes \brief Description of QML object type attributes Every QML object type has a defined set of attributes. Each instance of an object type is created with the set of attributes that have been defined for that object type. There are several different kinds of attributes which can be specified, which are described below. \section1 Attributes in Object Declarations An \l{qtqml-syntax-basics.html#object-declarations}{object declaration} in a QML document defines a new type. It also declares an object hierarchy that will be instantiated should an instance of that newly defined type be created. The set of QML object-type attribute types is as follows: \list \li the \e id attribute \li property attributes \li signal attributes \li signal handler attributes \li method attributes \li attached properties and attached signal handler attributes \li enumeration attributes \endlist These attributes are discussed in detail below. \section2 The \e id Attribute Every QML object type has exactly one \e id attribute. This attribute is provided by the language itself, and cannot be redefined or overridden by any QML object type. A value may be assigned to the \e id attribute of an object instance to allow that object to be identified and referred to by other objects. This \c id must begin with a lower-case letter or an underscore, and cannot contain characters other than letters, numbers and underscores. Below is a \l TextInput object and a \l Text object. The \l TextInput object's \c id value is set to "myTextInput". The \l Text object sets its \c text property to have the same value as the \c text property of the \l TextInput, by referring to \c myTextInput.text. Now, both items will display the same text: \qml import QtQuick 2.0 Column { width: 200; height: 200 TextInput { id: myTextInput; text: "Hello World" } Text { text: myTextInput.text } } \endqml An object can be referred to by its \c id from anywhere within the \e {component scope} in which it is declared. Therefore, an \c id value must always be unique within its component scope. See \l{qtqml-documents-scope.html}{Scope and Naming Resolution} for more information. Once an object instance is created, the value of its \e id attribute cannot be changed. While it may look like an ordinary property, the \c id attribute is \b{not} an ordinary \c property attribute, and special semantics apply to it; for example, it is not possible to access \c myTextInput.id in the above example. \section2 Property Attributes A property is an attribute of an object that can be assigned a static value or bound to a dynamic expression. A property's value can be read by other objects. Generally it can also be modified by another object, unless a particular QML type has explicitly disallowed this for a specific property. \section3 Defining Property Attributes A property may be defined for a type in C++ by registering a Q_PROPERTY of a class which is then registered with the QML type system. Alternatively, a custom property of an object type may be defined in an object declaration in a QML document with the following syntax: \code [default] [required] [readonly] property \endcode In this way an object declaration may \l {Defining Object Types from QML} {expose a particular value} to outside objects or maintain some internal state more easily. Property names must begin with a lower case letter and can only contain letters, numbers and underscores. \l {JavaScript Reserved Words} {JavaScript reserved words} are not valid property names. The \c default, \c required, and \c readonly keywords are optional, and modify the semantics of the property being declared. See the upcoming sections on \l {Default Properties}{default properties}, \l {Required Properties}{required properties} and, \l {Read-Only Properties}{read-only properties} for more information about their respective meaning. Declaring a custom property implicitly creates a value-change \l{Signal attributes}{signal} for that property, as well as an associated \l{Signal handler attributes}{signal handler} called \e onChanged, where \e is the name of the property, with the first letter capitalized. For example, the following object declaration defines a new type which derives from the Rectangle base type. It has two new properties, with a \l{Signal handler attributes}{signal handler} implemented for one of those new properties: \qml Rectangle { property color previousColor property color nextColor onNextColorChanged: console.log("The next color will be: " + nextColor.toString()) } \endqml \section4 Valid Types in Custom Property Definitions Any of the \l {QML Basic Types} aside from the \l enumeration type can be used as custom property types. For example, these are all valid property declarations: \qml Item { property int someNumber property string someString property url someUrl } \endqml (Enumeration values are simply whole number values and can be referred to with the \l int type instead.) Some basic types are provided by the \c QtQuick module and thus cannot be used as property types unless the module is imported. See the \l {QML Basic Types} documentation for more details. Note the \l var basic type is a generic placeholder type that can hold any type of value, including lists and objects: \code property var someNumber: 1.5 property var someString: "abc" property var someBool: true property var someList: [1, 2, "three", "four"] property var someObject: Rectangle { width: 100; height: 100; color: "red" } \endcode Additionally, any \l{QML Object Types}{QML object type} can be used as a property type. For example: \code property Item someItem property Rectangle someRectangle \endcode This applies to \l {Defining Object Types from QML}{custom QML types} as well. If a QML type was defined in a file named \c ColorfulButton.qml (in a directory which was then imported by the client), then a property of type \c ColorfulButton would also be valid. \section3 Assigning Values to Property Attributes The value of a property of an object instance may be specified in two separate ways: \list \li a value assignment on initialization \li an imperative value assignment \endlist In either case, the value may be either a \e static value or a \e {binding expression} value. \section4 Value Assignment on Initialization The syntax for assigning a value to a property on initialization is: \code : \endcode An initialization value assignment may be combined with a property definition in an object declaration, if desired. In that case, the syntax of the property definition becomes: \code [default] property : \endcode An example of property value initialization follows: \qml import QtQuick 2.0 Rectangle { color: "red" property color nextColor: "blue" // combined property declaration and initialization } \endqml \section4 Imperative Value Assignment An imperative value assignment is where a property value (either static value or binding expression) is assigned to a property from imperative JavaScript code. The syntax of an imperative value assignment is just the JavaScript assignment operator, as shown below: \code [.] = value \endcode An example of imperative value assignment follows: \qml import QtQuick 2.0 Rectangle { id: rect Component.onCompleted: { rect.color = "red" } } \endqml \section3 Static Values and Binding Expression Values As previously noted, there are two kinds of values which may be assigned to a property: \e static values, and \e {binding expression} values. The latter are also known as \l{Property Binding}{property bindings}. \table \header \li Kind \li Semantics \row \li Static Value \li A constant value which does not depend on other properties. \row \li Binding Expression \li A JavaScript expression which describes a property's relationship with other properties. The variables in this expression are called the property's \e dependencies. The QML engine enforces the relationship between a property and its dependencies. When any of the dependencies change in value, the QML engine automatically re-evaluates the binding expression and assigns the new result to the property. \endtable Here is an example that shows both kinds of values being assigned to properties: \qml import QtQuick 2.0 Rectangle { // both of these are static value assignments on initialization width: 400 height: 200 Rectangle { // both of these are binding expression value assignments on initialization width: parent.width / 2 height: parent.height } } \endqml \note To assign a binding expression imperatively, the binding expression must be contained in a function that is passed into \l{Qt::binding()}{Qt.binding()}, and then the value returned by Qt.binding() must be assigned to the property. In contrast, Qt.binding() must not be used when assigning a binding expression upon initialization. See \l{Property Binding} for more information. \section3 Type Safety Properties are type safe. A property can only be assigned a value that matches the property type. For example, if a property is a real, and if you try to assign a string to it, you will get an error: \code property int volume: "four" // generates an error; the property's object will not be loaded \endcode Likewise if a property is assigned a value of the wrong type during run time, the new value will not be assigned, and an error will be generated. Some property types do not have a natural value representation, and for those property types the QML engine automatically performs string-to-typed-value conversion. So, for example, even though properties of the \c color type store colors and not strings, you are able to assign the string \c "red" to a color property, without an error being reported. See \l {QML Basic Types} for a list of the types of properties that are supported by default. Additionally, any available \l {QML Object Types} {QML object type} may also be used as a property type. \section3 Special Property Types \section4 Object List Property Attributes A \l list type property can be assigned a list of QML object-type values. The syntax for defining an object list value is a comma-separated list surrounded by square brackets: \code [ , , ... ] \endcode For example, the \l Item type has a \l {Item::states}{states} property that is used to hold a list of \l State type objects. The code below initializes the value of this property to a list of three \l State objects: \qml import QtQuick 2.0 Item { states: [ State { name: "loading" }, State { name: "running" }, State { name: "stopped" } ] } \endqml If the list contains a single item, the square brackets may be omitted: \qml import QtQuick 2.0 Item { states: State { name: "running" } } \endqml A \l list type property may be specified in an object declaration with the following syntax: \code [default] property list<> propertyName \endcode and, like other property declarations, a property initialization may be combined with the property declaration with the following syntax: \code [default] property list<> propertyName: \endcode An example of list property declaration follows: \qml import QtQuick 2.0 Rectangle { // declaration without initialization property list siblingRects // declaration with initialization property list childRects: [ Rectangle { color: "red" }, Rectangle { color: "blue"} ] } \endqml If you wish to declare a property to store a list of values which are not necessarily QML object-type values, you should declare a \l var property instead. \section4 Grouped Properties In some cases properties contain a logical group of sub-property attributes. These sub-property attributes can be assigned to using either the dot notation or group notation. For example, the \l Text type has a \l{Text::font.family}{font} group property. Below, the first \l Text object initializes its \c font values using dot notation, while the second uses group notation: \code Text { //dot notation font.pixelSize: 12 font.b: true } Text { //group notation font { pixelSize: 12; b: true } } \endcode Grouped property types are basic types which have subproperties. Some of these basic types are provided by the QML language, while others may only be used if the Qt Quick module is imported. See the documentation about \l{QML Basic Types} for more information. \section3 Property Aliases Property aliases are properties which hold a reference to another property. Unlike an ordinary property definition, which allocates a new, unique storage space for the property, a property alias connects the newly declared property (called the aliasing property) as a direct reference to an existing property (the aliased property). A property alias declaration looks like an ordinary property definition, except that it requires the \c alias keyword instead of a property type, and the right-hand-side of the property declaration must be a valid alias reference: \code [default] property alias : \endcode Unlike an ordinary property, an alias has the following restrictions: \list \li It can only refer to an object, or the property of an object, that is within the scope of the \l{QML Object Types} {type} within which the alias is declared. \li It cannot contain arbitrary JavaScript expressions \li It cannot refer to objects declared outside of the scope of its type. \li The \e {alias reference} is not optional, unlike the optional default value for an ordinary property; the alias reference must be provided when the alias is first declared. \li It cannot refer to \l {Attached Properties and Attached Signal Handlers} {attached properties}. \li It cannot refer to properties inside a hierarchy with depth 3 or greater. The following code will not work: \code property alias color: myItem.myRect.border.color Item { id: myItem property Rectangle myRect } \endcode However, aliases to properties that are up to two levels deep will work. \code property alias color: rectangle.border.color Rectangle { id: rectangle } \endcode \endlist For example, below is a \c Button type with a \c buttonText aliased property which is connected to the \c text object of the \l Text child: \qml // Button.qml import QtQuick 2.0 Rectangle { property alias buttonText: textItem.text width: 100; height: 30; color: "yellow" Text { id: textItem } } \endqml The following code would create a \c Button with a defined text string for the child \l Text object: \qml Button { buttonText: "Click Me" } \endqml Here, modifying \c buttonText directly modifies the textItem.text value; it does not change some other value that then updates textItem.text. If \c buttonText was not an alias, changing its value would not actually change the displayed text at all, as property bindings are not bi-directional: the \c buttonText value would have changed if textItem.text was changed, but not the other way around. \section4 Considerations for Property Aliases Aliases are only activated once a component has been fully initialized. An error is generated when an uninitialized alias is referenced. Likewise, aliasing an aliasing property will also result in an error. \snippet qml/properties.qml alias complete When importing a \l{QML Object Types}{QML object type} with a property alias in the root object, however, the property appear as a regular Qt property and consequently can be used in alias references. It is possible for an aliasing property to have the same name as an existing property, effectively overwriting the existing property. For example, the following QML type has a \c color alias property, named the same as the built-in \l {Rectangle::color} property: \snippet qml/properties.qml alias overwrite Any object that use this type and refer to its \c color property will be referring to the alias rather than the ordinary \l {Rectangle::color} property. Internally, however, the rectangle can correctly set its \c color property and refer to the actual defined property rather than the alias. \section4 Property Aliases and Types Property aliases cannot have explicit type specifications. The type of a property alias is the \e declared type of the property or object it refers to. Therefore, if you create an alias to an object referenced via id with extra properties declared inline, the extra properties won't be accessible through the alias: \qml // MyItem.qml Item { property alias inner: innerItem Item { id: innerItem property int extraProperty } } \endqml You cannot initialize \a inner.extraProperty from outside of this component, as inner is only an \a Item: \qml // main.qml MyItem { inner.extraProperty: 5 // fails } \endqml However, if you extract the inner object into a separate component with a dedicated .qml file, you can instantiate that component instead and have all its properties available through the alias: \qml // MainItem.qml Item { // Now you can access inner.extraProperty, as inner is now an ExtraItem property alias inner: innerItem ExtraItem { id: innerItem } } // ExtraItem.qml Item { property int extraProperty } \endqml \section3 Default Properties An object definition can have a single \e default property. A default property is the property to which a value is assigned if an object is declared within another object's definition without declaring it as a value for a particular property. Declaring a property with the optional \c default keyword marks it as the default property. For example, say there is a file MyLabel.qml with a default property \c someText: \qml // MyLabel.qml import QtQuick 2.0 Text { default property var someText text: "Hello, " + someText.text } \endqml The \c someText value could be assigned to in a \c MyLabel object definition, like this: \qml MyLabel { Text { text: "world!" } } \endqml This has exactly the same effect as the following: \qml MyLabel { someText: Text { text: "world!" } } \endqml However, since the \c someText property has been marked as the default property, it is not necessary to explicitly assign the \l Text object to this property. You will notice that child objects can be added to any \l {Item}-based type without explicitly adding them to the \l {Item::children}{children} property. This is because the default property of \l Item is its \c data property, and any items added to this list for an \l Item are automatically added to its list of \l {Item::children}{children}. Default properties can be useful for reassigning the children of an item. See the \l{TabWidget Example}, which uses a default property to automatically reassign children of the TabWidget as children of an inner ListView. See also \l {Extending QML}. \section3 Required Properties An object declaration may define a property as required, using the \c required keyword. The syntax is \code required property \endcode As the name suggests, required properties must be set when an instance of the object is created. Violation of this rule will result in QML applications not starting if it can be detected statically. In case of dynamically instantiated QML components (for instance via \l {QtQml::Qt::createComponent()}{Qt.createComponent()}), violating this rule results in a warning and a null return value. It's possible to make an existing property required with \code required \endcode The following example shows how to create a custom Rectangle component, in which the color property always needs to be specified. \qml // ColorRectangle.qml Rectangle { required color } \endqml \note You can't assign an initial value to a required property from QML, as that would go directly against the intended usage of required properties. Required properties play a special role in model-view-delegate code: If the delegate of a view has required properties whose names match with the role names of the view's model, then those properties will be initialized with the model's corresponding values. For more information, visit the \l{Models and Views in Qt Quick} page. \sa {QQmlComponent::createWithInitialProperties}, {QQmlApplicationEngine::setInitialProperties} and {QQuickView::setInitialProperties} for ways to initialize required properties from C++. \section3 Read-Only Properties An object declaration may define a read-only property using the \c readonly keyword, with the following syntax: \code readonly property : \endcode Read-only properties must be assigned a value on initialization. After a read-only property is initialized, it no longer possible to give it a value, whether from imperative code or otherwise. For example, the code in the \c Component.onCompleted block below is invalid: \qml Item { readonly property int someNumber: 10 Component.onCompleted: someNumber = 20 // doesn't work, causes an error } \endqml \note A read-only property cannot also be a \l{Default Properties}{default} property. \section3 Property Modifier Objects Properties can have \l{qtqml-cppintegration-definetypes.html#property-modifier-types} {property value modifier objects} associated with them. The syntax for declaring an instance of a property modifier type associated with a particular property is as follows: \code on { // attributes of the object instance } \endcode It is important to note that the above syntax is in fact an \l{qtqml-syntax-basics.html#object-declarations}{object declaration} which will instantiate an object which acts on a pre-existing property. Certain property modifier types may only be applicable to specific property types, however this is not enforced by the language. For example, the \c NumberAnimation type provided by \c QtQuick will only animate numeric-type (such as \c int or \c real) properties. Attempting to use a \c NumberAnimation with non-numeric property will not result in an error, however the non-numeric property will not be animated. The behavior of a property modifier type when associated with a particular property type is defined by its implementation. \section2 Signal Attributes A signal is a notification from an object that some event has occurred: for example, a property has changed, an animation has started or stopped, or when an image has been downloaded. The \l MouseArea type, for example, has a \l {MouseArea::}{clicked} signal that is emitted when the user clicks within the mouse area. An object can be notified through a \l{Signal handler attributes} {signal handler} whenever a particular signal is emitted. A signal handler is declared with the syntax \e on where \e is the name of the signal, with the first letter capitalized. The signal handler must be declared within the definition of the object that emits the signal, and the handler should contain the block of JavaScript code to be executed when the signal handler is invoked. For example, the \e onClicked signal handler below is declared within the \l MouseArea object definition, and is invoked when the \l MouseArea is clicked, causing a console message to be printed: \qml import QtQuick 2.0 Item { width: 100; height: 100 MouseArea { anchors.fill: parent onClicked: { console.log("Click!") } } } \endqml \section3 Defining Signal Attributes A signal may be defined for a type in C++ by registering a Q_SIGNAL of a class which is then registered with the QML type system. Alternatively, a custom signal for an object type may be defined in an object declaration in a QML document with the following syntax: \code signal [([ [, ...]])] \endcode Attempting to declare two signals or methods with the same name in the same type block is an error. However, a new signal may reuse the name of an existing signal on the type. (This should be done with caution, as the existing signal may be hidden and become inaccessible.) Here are three examples of signal declarations: \qml import QtQuick 2.0 Item { signal clicked signal hovered() signal actionPerformed(string action, var actionResult) } \endqml If the signal has no parameters, the "()" brackets are optional. If parameters are used, the parameter types must be declared, as for the \c string and \c var arguments for the \c actionPerformed signal above. The allowed parameter types are the same as those listed under \l {Defining Property Attributes} on this page. To emit a signal, invoke it as a method. Any relevant \l{Signal handler attributes}{signal handlers} will be invoked when the signal is emitted, and handlers can use the defined signal argument names to access the respective arguments. \section3 Property Change Signals QML types also provide built-in \e {property change signals} that are emitted whenever a property value changes, as previously described in the section on \l{Property attributes}{property attributes}. See the upcoming section on \l{Property change signal handlers}{property change signal handlers} for more information about why these signals are useful, and how to use them. \section2 Signal Handler Attributes Signal handlers are a special sort of \l{Method attributes}{method attribute}, where the method implementation is invoked by the QML engine whenever the associated signal is emitted. Adding a signal to an object definition in QML will automatically add an associated signal handler to the object definition, which has, by default, an empty implementation. Clients can provide an implementation, to implement program logic. Consider the following \c SquareButton type, whose definition is provided in the \c SquareButton.qml file as shown below, with signals \c activated and \c deactivated: \qml // SquareButton.qml Rectangle { id: root signal activated(real xPosition, real yPosition) signal deactivated property int side: 100 width: side; height: side MouseArea { anchors.fill: parent onPressed: root.activated(mouse.x, mouse.y) onReleased: root.deactivated() } } \endqml These signals could be received by any \c SquareButton objects in another QML file in the same directory, where implementations for the signal handlers are provided by the client: \qml // myapplication.qml SquareButton { onActivated: console.log("Activated at " + xPosition + "," + yPosition) onDeactivated: console.log("Deactivated!") } \endqml See the \l {Signal and Handler Event System} for more details on use of signals. \section3 Property Change Signal Handlers Signal handlers for property change signal take the syntax form \e onChanged where \e is the name of the property, with the first letter capitalized. For example, although the \l TextInput type documentation does not document a \c textChanged signal, this signal is implicitly available through the fact that \l TextInput has a \l {TextInput::text}{text} property and so it is possible to write an \c onTextChanged signal handler to be called whenever this property changes: \qml import QtQuick 2.0 TextInput { text: "Change this!" onTextChanged: console.log("Text has changed to:", text) } \endqml \section2 Method Attributes A method of an object type is a function which may be called to perform some processing or trigger further events. A method can be connected to a signal so that it is automatically invoked whenever the signal is emitted. See \l {Signal and Handler Event System} for more details. \section3 Defining Method Attributes A method may be defined for a type in C++ by tagging a function of a class which is then registered with the QML type system with Q_INVOKABLE or by registering it as a Q_SLOT of the class. Alternatively, a custom method can be added to an object declaration in a QML document with the following syntax: \code function ([[, ...]]) { } \endcode Methods can be added to a QML type in order to define standalone, reusable blocks of JavaScript code. These methods can be invoked either internally or by external objects. Unlike signals, method parameter types do not have to be declared as they default to the \c var type. Attempting to declare two methods or signals with the same name in the same type block is an error. However, a new method may reuse the name of an existing method on the type. (This should be done with caution, as the existing method may be hidden and become inaccessible.) Below is a \l Rectangle with a \c calculateHeight() method that is called when assigning the \c height value: \qml import QtQuick 2.0 Rectangle { id: rect function calculateHeight() { return rect.width / 2; } width: 100 height: calculateHeight() } \endqml If the method has parameters, they are accessible by name within the method. Below, when the \l MouseArea is clicked it invokes the \c moveTo() method which can then refer to the received \c newX and \c newY parameters to reposition the text: \qml import QtQuick 2.0 Item { width: 200; height: 200 MouseArea { anchors.fill: parent onClicked: label.moveTo(mouse.x, mouse.y) } Text { id: label function moveTo(newX, newY) { label.x = newX; label.y = newY; } text: "Move me!" } } \endqml \section2 Attached Properties and Attached Signal Handlers \e {Attached properties} and \e {attached signal handlers} are mechanisms that enable objects to be annotated with extra properties or signal handlers that are otherwise unavailable to the object. In particular, they allow objects to access properties or signals that are specifically relevant to the individual object. A QML type implementation may choose to \l {Providing Attached Properties}{create an \e {attaching type} in C++} with particular properties and signals. Instances of this type can then be created and \e attached to specific objects at run time, allowing those objects to access the properties and signals of the attaching type. These are accessed by prefixing the properties and respective signal handlers with the name of the attaching type. References to attached properties and handlers take the following syntax form: \code . .on \endcode For example, the \l ListView type has an attached property \l {ListView::isCurrentItem}{ListView.isCurrentItem} that is available to each delegate object in a ListView. This can be used by each individual delegate object to determine whether it is the currently selected item in the view: \qml import QtQuick 2.0 ListView { width: 240; height: 320 model: 3 delegate: Rectangle { width: 100; height: 30 color: ListView.isCurrentItem ? "red" : "yellow" } } \endqml In this case, the name of the \e {attaching type} is \c ListView and the property in question is \c isCurrentItem, hence the attached property is referred to as \c ListView.isCurrentItem. An attached signal handler is referred to in the same way. For example, the \l{Component::completed}{Component.onCompleted} attached signal handler is commonly used to execute some JavaScript code when a component's creation process has been completed. In the example below, once the \l ListModel has been fully created, its \c Component.onCompleted signal handler will automatically be invoked to populate the model: \qml import QtQuick 2.0 ListView { width: 240; height: 320 model: ListModel { id: listModel Component.onCompleted: { for (var i = 0; i < 10; i++) listModel.append({"Name": "Item " + i}) } } delegate: Text { text: index } } \endqml Since the name of the \e {attaching type} is \c Component and that type has a \l{Component::completed}{completed} signal, the attached signal handler is referred to as \c Component.onCompleted. \section3 A Note About Accessing Attached Properties and Signal Handlers A common error is to assume that attached properties and signal handlers are directly accessible from the children of the object to which these attributes have been attached. This is not the case. The instance of the \e {attaching type} is only attached to specific objects, not to the object and all of its children. For example, below is a modified version of the earlier example involving attached properties. This time, the delegate is an \l Item and the colored \l Rectangle is a child of that item: \qml import QtQuick 2.0 ListView { width: 240; height: 320 model: 3 delegate: Item { width: 100; height: 30 Rectangle { width: 100; height: 30 color: ListView.isCurrentItem ? "red" : "yellow" // WRONG! This won't work. } } } \endqml This does not work as expected because \c ListView.isCurrentItem is attached \e only to the root delegate object, and not its children. Since the \l Rectangle is a child of the delegate, rather than being the delegate itself, it cannot access the \c isCurrentItem attached property as \c ListView.isCurrentItem. So instead, the rectangle should access \c isCurrentItem through the root delegate: \qml ListView { //.... delegate: Item { id: delegateItem width: 100; height: 30 Rectangle { width: 100; height: 30 color: delegateItem.ListView.isCurrentItem ? "red" : "yellow" // correct } } } \endqml Now \c delegateItem.ListView.isCurrentItem correctly refers to the \c isCurrentItem attached property of the delegate. \section2 Enumeration Attributes Enumerations provide a fixed set of named choices. They can be declared in QML using the \c enum keyword: \qml // MyText.qml Text { enum TextType { Normal, Heading } } \endqml As shown above, enumeration types (e.g. \c TextType) and values (e.g. \c Normal) must begin with an uppercase letter. Values are referred to via \c {..} or \c {.}. \qml // MyText.qml Text { enum TextType { Normal, Heading } property int textType: MyText.TextType.Normal font.bold: textType == MyText.TextType.Heading font.pixelSize: textType == MyText.TextType.Heading ? 24 : 12 } \endqml More information on enumeration usage in QML can be found in the \l {QML Basic Types} \l enumeration documentation. The ability to declare enumerations in QML was introduced in Qt 5.10. */