Qt 4.8: QML PathView Element

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# QML PathView Element

The PathView element lays out model-provided items on a path. More...

Inherits Item

This element was introduced in Qt 4.7.

- List of all members, including inherited members

## Properties

- count : int
- currentIndex : int
- delegate : Component
- dragMargin : real
- flickDeceleration : real
- flicking : bool
- highlight : Component
- highlightItem : Item
- highlightMoveDuration : int
- highlightRangeMode : enumeration
- interactive : bool
- model : model
- moving : bool
- offset : real
- path : Path
- pathItemCount : int
- preferredHighlightBegin : real
- preferredHighlightEnd : real

## Attached Properties

- isCurrentItem : bool
- onPath : bool
- view : PathView

## Signal Handlers

- onFlickEnded
- onFlickStarted
- onMovementEnded
- onMovementStarted

## Methods

- decrementCurrentIndex
- incrementCurrentIndex

## Detailed Description

A PathView displays data from models created from built-in QML elements like ListModel and XmlListModel, or custom model classes defined in C++ that inherit from QAbstractListModel.

The view has a model, which defines the data to be displayed, and a delegate, which defines how the data should be displayed. The delegate is instantiated for each item on the path. The items may be flicked to move them along the path.

For example, if there is a simple list model defined in a file `ContactModel.qml` like this:

     import QtQuick 1.0

     ListModel {
         ListElement {
             name: "Bill Jones"
             icon: "pics/qtlogo.png"
         }
         ListElement {
             name: "Jane Doe"
             icon: "pics/qtlogo.png"
         }
         ListElement {
             name: "John Smith"
             icon: "pics/qtlogo.png"
         }
     }

This data can be represented as a PathView, like this:

     import QtQuick 1.0

     Rectangle {
         width: 240; height: 200

         Component {
             id: delegate
             Column {
                 id: wrapper
                 Image {
                     anchors.horizontalCenter: nameText.horizontalCenter
                     width: 64; height: 64
                     source: icon
                 }
                 Text {
                     id: nameText
                     text: name
                     font.pointSize: 16
                     color: wrapper.PathView.isCurrentItem ? "red" : "black"
                 }
             }
         }

         PathView {
             anchors.fill: parent
             model: ContactModel {}
             delegate: delegate
             path: Path {
                 startX: 120; startY: 100
                 PathQuad { x: 120; y: 25; controlX: 260; controlY: 75 }
                 PathQuad { x: 120; y: 100; controlX: -20; controlY: 75 }
             }
         }
     }

(Note the above example uses PathAttribute to scale and modify the opacity of the items as they rotate. This additional code can be seen in the PathAttribute documentation.)

PathView does not automatically handle keyboard navigation. This is because the keys to use for navigation will depend upon the shape of the path. Navigation can be added quite simply by setting `focus` to `true` and calling decrementCurrentIndex() or incrementCurrentIndex(), for example to navigate using the left and right arrow keys:

     PathView {
         // ...
         focus: true
         Keys.onLeftPressed: decrementCurrentIndex()
         Keys.onRightPressed: incrementCurrentIndex()
     }

The path view itself is a focus scope (see the focus documentation page for more details).

Delegates are instantiated as needed and may be destroyed at any time. State should never be stored in a delegate.

PathView attaches a number of properties to the root item of the delegate, for example `PathView.isCurrentItem`. In the following example, the root delegate item can access this attached property directly as `PathView.isCurrentItem`, while the child `nameText` object must refer to this property as `wrapper.PathView.isCurrentItem`.

         Component {
             id: delegate
             Column {
                 id: wrapper
                 Image {
                     anchors.horizontalCenter: nameText.horizontalCenter
                     width: 64; height: 64
                     source: icon
                 }
                 Text {
                     id: nameText
                     text: name
                     font.pointSize: 16
                     color: wrapper.PathView.isCurrentItem ? "red" : "black"
                 }
             }
         }

Note that views do not enable clip automatically. If the view is not clipped by another item or the screen, it will be necessary to set clip: true in order to have the out of view items clipped nicely.

See also Path and PathView example.

## Property Documentation

read-onlycount : int

This property holds the number of items in the model.

currentIndex : int

This property holds the index of the current item.

delegate : Component

The delegate provides a template defining each item instantiated by the view. The index is exposed as an accessible `index` property. Properties of the model are also available depending upon the type of Data Model.

The number of elements in the delegate has a direct effect on the flicking performance of the view when pathItemCount is specified. If at all possible, place functionality that is not needed for the normal display of the delegate in a Loader which can load additional elements when needed.

Note that the PathView will layout the items based on the size of the root item in the delegate.

Here is an example delegate:

         Component {
             id: delegate
             Column {
                 id: wrapper
                 Image {
                     anchors.horizontalCenter: nameText.horizontalCenter
                     width: 64; height: 64
                     source: icon
                 }
                 Text {
                     id: nameText
                     text: name
                     font.pointSize: 16
                     color: wrapper.PathView.isCurrentItem ? "red" : "black"
                 }
             }
         }

dragMargin : real

This property holds the maximum distance from the path that initiate mouse dragging.

By default the path can only be dragged by clicking on an item. If dragMargin is greater than zero, a drag can be initiated by clicking within dragMargin pixels of the path.

flickDeceleration : real

This property holds the rate at which a flick will decelerate.

The default is 100.

read-onlyflicking : bool

This property holds whether the view is currently moving due to the user flicking the view.

highlight : Component

This property holds the component to use as the highlight.

An instance of the highlight component will be created for each view. The geometry of the resultant component instance will be managed by the view so as to stay with the current item.

The below example demonstrates how to make a simple highlight. Note the use of the PathView.onPath attached property to ensure that the highlight is hidden when flicked away from the path.

     Component {
         Rectangle {
             visible: PathView.onPath
             // ...
         }
     }

See also highlightItem and highlightRangeMode.

read-onlyhighlightItem : Item

`highlightItem` holds the highlight item, which was created from the highlight component.

See also highlight.

highlightMoveDuration : int

This property holds the move animation duration of the highlight delegate.

If the highlightRangeMode is StrictlyEnforceRange then this property determines the speed that the items move along the path.

The default value for the duration is 300ms.

interactive : bool

A user cannot drag or flick a PathView that is not interactive.

This property is useful for temporarily disabling flicking. This allows special interaction with PathView's children.

model : model

This property holds the model providing data for the view.

The model provides a set of data that is used to create the items for the view. For large or dynamic datasets the model is usually provided by a C++ model object. Models can also be created directly in QML, using the ListModel element.

Note: changing the model will reset the offset and currentIndex to 0.

See also Data Models.

read-onlymoving : bool

This property holds whether the view is currently moving due to the user either dragging or flicking the view.

offset : real

The offset specifies how far along the path the items are from their initial positions. This is a real number that ranges from 0.0 to the count of items in the model.

path : Path

This property holds the path used to lay out the items. For more information see the Path documentation.

pathItemCount : int

This property holds the number of items visible on the path at any one time.

preferredHighlightBegin : real
preferredHighlightEnd : real
highlightRangeMode : enumeration

These properties set the preferred range of the highlight (current item) within the view. The preferred values must be in the range 0.0-1.0.

If highlightRangeMode is set to PathView.NoHighlightRange

If highlightRangeMode is set to PathView.ApplyRange the view will attempt to maintain the highlight within the range, however the highlight can move outside of the range at the ends of the path or due to a mouse interaction.

If highlightRangeMode is set to PathView.StrictlyEnforceRange the highlight will never move outside of the range. This means that the current item will change if a keyboard or mouse action would cause the highlight to move outside of the range.

Note that this is the correct way to influence where the current item ends up when the view moves. For example, if you want the currently selected item to be in the middle of the path, then set the highlight range to be 0.5,0.5 and highlightRangeMode to PathView.StrictlyEnforceRange. Then, when the path scrolls, the currently selected item will be the item at that position. This also applies to when the currently selected item changes - it will scroll to within the preferred highlight range. Furthermore, the behaviour of the current item index will occur whether or not a highlight exists.

The default value is PathView.StrictlyEnforceRange.

Note that a valid range requires preferredHighlightEnd to be greater than or equal to preferredHighlightBegin.

## Attached Property Documentation

read-onlyPathView.isCurrentItem : bool

This attached property is true if this delegate is the current item; otherwise false.

It is attached to each instance of the delegate.

This property may be used to adjust the appearance of the current item.

         Component {
             id: delegate
             Column {
                 id: wrapper
                 Image {
                     anchors.horizontalCenter: nameText.horizontalCenter
                     width: 64; height: 64
                     source: icon
                 }
                 Text {
                     id: nameText
                     text: name
                     font.pointSize: 16
                     color: wrapper.PathView.isCurrentItem ? "red" : "black"
                 }
             }
         }

read-onlyPathView.onPath : bool

This attached property holds whether the item is currently on the path.

If a pathItemCount has been set, it is possible that some items may be instantiated, but not considered to be currently on the path. Usually, these items would be set invisible, for example:

     Component {
         Rectangle {
             visible: PathView.onPath
             // ...
         }
     }

It is attached to each instance of the delegate.

PathView.view : PathView

This attached property holds the view that manages this delegate instance.

It is attached to each instance of the delegate.

## Signal Handler Documentation

PathView::onFlickEnded ()

This handler is called when the view stops moving due to a flick.

PathView::onFlickStarted ()

This handler is called when the view is flicked. A flick starts from the point that the mouse or touch is released, while still in motion.

PathView::onMovementEnded ()

This handler is called when the view stops moving due to user interaction. If a flick was generated, this handler will be triggered once the flick stops. If a flick was not generated, the handler will be triggered when the user stops dragging - i.e. a mouse or touch release.

PathView::onMovementStarted ()

This handler is called when the view begins moving due to user interaction.

## Method Documentation

PathView::decrementCurrentIndex ()

Decrements the current index.

Note: methods should only be called after the Component has completed.

PathView::incrementCurrentIndex ()

Increments the current index.

Note: methods should only be called after the Component has completed.