QML ListModel Element

The ListModel element defines a free-form list data source. More...

Properties

• count : int

Methods

• append
• clear
• get
• insert
• move
• remove
• set
• setProperty
• 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 Qt 4.7

 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 Qt 4.7

 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() 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:

 import Qt 4.7

 Rectangle {
     color: "white"
     width: 200
     height: 300

     ListView {
         anchors.fill: parent
         model: listModel
         delegate: Component {
             Text { text: time }
         }

         ListModel { id: listModel }

         WorkerScript {
             id: worker
             source: "dataloader.js"
         }

         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.js, 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.js, which appends the current time to the list model.

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

Restrictions

If a list model is to be accessed from a WorkerScript, it cannot contain list-type data. So, the following model cannot be used from a WorkerScript because of the list contained in the "attributes" property:

 ListModel {
     id: fruitModel
     ListElement {
         name: "Apple"
         cost: 2.45
         attributes: [
             ListElement { description: "Core" },
             ListElement { description: "Deciduous" }
         ]
     }
 }

In addition, the WorkerScript cannot add list-type data to the model.

See also Data Models, Threaded ListModel example, and QtDeclarative.

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)