内容

特性
方法
详细描述
用法范例
修改列表模型
采用 WorkerScript 使用线程化列表模型
限定

ListModel QML Element

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

Since:

Qt 4.7

所有成员列表，包括继承成员

特性

count : int

方法

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

详细描述

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.

用法范例

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

import QtQuick 1.0
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 1.0
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 }
            }
        }
    }
}

修改列表模型

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.

采用 WorkerScript 使用线程化列表模型

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.

这里的范例使用 WorkerScript to periodically append the current time to a list model:

包括文件， dataloader.js ，看起来像这样：

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() 从 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.

限定

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" }
        ]
    }
}

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

另请参阅 数据模型 , Threaded ListModel example ，和 QtDeclarative .

特性文档编制

count : int

The number of data entries in the model.

方法文档编制

append ( jsobject dict )

Adds a new item to the end of the list model, with the values in dict .

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

另请参阅 set() and remove() .

clear ()

Deletes all content from the model.

另请参阅 append() and remove() .

对象 get ( int index )

返回项在 index in the list model. This allows the item data to be accessed or modified from JavaScript:

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

The index must be an element in the list.

Note that properties of the returned object that are themselves objects will also be models, and this get() method is used to access elements:

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

警告： The returned object is not guaranteed to remain valid. It should not be used in 特性绑定 .

另请参阅 append() .

insert ( int index , jsobject dict )

Adds a new item to the list model at position index , with the values in dict .

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

The index must be to an existing item in the list, or one past the end of the list (equivalent to append).

另请参阅 set() and append() .

move ( int from , int to , int n )

移动 n 项 from one position to another.

The from and to ranges must exist; for example, to move the first 3 items to the end of the list:

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

另请参阅 append() .

remove ( int index )

Deletes the content at index from the model.

另请参阅 clear() .

set ( int index , jsobject dict )

Changes the item at index in the list model with the values in dict . Properties not appearing in dict are left unchanged.

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

若 index is equal to count() then a new item is appended to the list. Otherwise, index must be an element in the list.

另请参阅 append() .

setProperty ( int index , string property , variant value )

改变 property of the item at index in the list model to value .

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

The index must be an element in the list.

另请参阅 append() .

sync ()

Writes any unsaved changes to the list model after it has been modified from a worker script.