ListModel QML Type

Defines a free-form list data source. More...

• List of all members, including inherited members

Properties

• count : int
• dynamicRoles : bool

Methods

• append(jsobject dict)
• clear()
• object get(int index)
• insert(int index, jsobject dict)
• move(int from, int to, int n)
• remove(int index, int count)
• set(int index, jsobject dict)
• setProperty(int index, string property, variant value)
• sync()

Detailed Description

The ListModel is a simple container of ListElement definitions, each containing data roles. The contents can be defined dynamically, or explicitly in QML.

The number of elements in the model can be obtained from its count property. A number of familiar methods are also provided to manipulate the contents of the model, including append(), insert(), move(), remove() and set(). These methods accept dictionaries as their arguments; these are translated to ListElement objects by the model.

Elements can be manipulated via the model using the setProperty() method, which allows the roles of the specified element to be set and changed.

Example Usage

The following example shows a ListModel containing three elements, with the roles "name" and "cost".

 import QtQuick 2.0

 ListModel {
     id: fruitModel

     ListElement {
         name: "Apple"
         cost: 2.45
     }
     ListElement {
         name: "Orange"
         cost: 3.25
     }
     ListElement {
         name: "Banana"
         cost: 1.95
     }
 }

Roles (properties) in each element must begin with a lower-case letter and should be common to all elements in a model. The ListElement documentation provides more guidelines for how elements should be defined.

Since the example model contains an id property, it can be referenced by views, such as the ListView in this example:

 import QtQuick 2.0

 Rectangle {
     width: 200; height: 200

     ListModel {
         id: fruitModel
         ...
     }

     Component {
         id: fruitDelegate
         Row {
             spacing: 10
             Text { text: name }
             Text { text: '$' + cost }
         }
     }

     ListView {
         anchors.fill: parent
         model: fruitModel
         delegate: fruitDelegate
     }
 }

It is possible for roles to contain list data. In the following example we create a list of fruit attributes:

 ListModel {
     id: fruitModel

     ListElement {
         name: "Apple"
         cost: 2.45
         attributes: [
             ListElement { description: "Core" },
             ListElement { description: "Deciduous" }
         ]
     }
     ListElement {
         name: "Orange"
         cost: 3.25
         attributes: [
             ListElement { description: "Citrus" }
         ]
     }
     ListElement {
         name: "Banana"
         cost: 1.95
         attributes: [
             ListElement { description: "Tropical" },
             ListElement { description: "Seedless" }
         ]
     }
 }

The delegate displays all the fruit attributes:

 Component {
     id: fruitDelegate
     Item {
         width: 200; height: 50
         Text { id: nameField; text: name }
         Text { text: '$' + cost; anchors.left: nameField.right }
         Row {
             anchors.top: nameField.bottom
             spacing: 5
             Text { text: "Attributes:" }
             Repeater {
                 model: attributes
                 Text { text: description }
             }
         }
     }
 }

Modifying List Models

The content of a ListModel may be created and modified using the clear(), append(), set(), insert() and setProperty() methods. For example:

     Component {
         id: fruitDelegate
         Item {
             width: 200; height: 50
             Text { text: name }
             Text { text: '$' + cost; anchors.right: parent.right }

             // Double the price when clicked.
             MouseArea {
                 anchors.fill: parent
                 onClicked: fruitModel.setProperty(index, "cost", cost * 2)
             }
         }
     }

Note that when creating content dynamically the set of available properties cannot be changed once set. Whatever properties are first added to the model are the only permitted properties in the model.

Using Threaded List Models with WorkerScript

ListModel can be used together with WorkerScript access a list model from multiple threads. This is useful if list modifications are synchronous and take some time: the list operations can be moved to a different thread to avoid blocking of the main GUI thread.

Here is an example that uses WorkerScript to periodically append the current time to a list model:

         Timer {
             id: timer
             interval: 2000; repeat: true
             running: true
             triggeredOnStart: true

             onTriggered: {
                 var msg = {'action': 'appendCurrentTime', 'model': listModel};
                 worker.sendMessage(msg);
             }
         }

The included file, dataloader.mjs, looks like this:

 WorkerScript.onMessage = function(msg) {
     if (msg.action == 'appendCurrentTime') {
         var data = {'time': new Date().toTimeString()};
         msg.model.append(data);
         msg.model.sync();   // updates the changes to the list
     }
 }

The timer in the main example sends messages to the worker script by calling WorkerScript::sendMessage(). When this message is received, WorkerScript.onMessage() is invoked in dataloader.mjs, which appends the current time to the list model.

Note the call to sync() from the external thread. You must call sync() or else the changes made to the list from that thread will not be reflected in the list model in the main thread.

See also Data Models, Qt Quick Examples - Threading, and Qt QML.

Property Documentation

Method Documentation

 fruitModel.append({"cost": 5.95, "name":"Pizza"})

 Component.onCompleted: {
     fruitModel.append({"cost": 5.95, "name":"Jackfruit"});
     console.log(fruitModel.get(0).cost);
     fruitModel.get(0).cost = 10.95;
 }

 fruitModel.append(..., "attributes":
     [{"name":"spikes","value":"7mm"},
      {"name":"color","value":"green"}]);
 fruitModel.get(0).attributes.get(1).value; // == "green"

 fruitModel.insert(2, {"cost": 5.95, "name":"Pizza"})

 fruitModel.move(0, fruitModel.count - 3, 3)

 fruitModel.set(3, {"cost": 5.95, "name":"Pizza"})

 fruitModel.setProperty(3, "cost", 5.95)