内容

• 特性
• 附加信号
• 方法
• 详细描述
• 创建上下文

Component QML 类型

封装 QML 组件定义 更多...

• 所有成员列表，包括继承成员

特性

• progress : real
• status : enumeration
• url : url

附加信号

• completed ()
• destruction ()

方法

• 对象 createObject (QtObject parent , object properties )
• string errorString ()
• 对象 incubateObject (Item parent , object properties , enumeration mode )

详细描述

Component 是可重用，具有良好定义接口的 QML 封装类型。

Components 的定义经常是通过 组件文件 - that is, .qml files. The 组件 type essentially allows QML components to be defined inline, within a QML 文档 , rather than as a separate QML file. This may be useful for reusing a small component within a QML file, or for defining a component that logically belongs with other QML components within a file.

For example, here is a component that is used by multiple Loader objects. It contains a single item, a Rectangle :

import QtQuick 2.0
Item {
    width: 100; height: 100
    Component {
        id: redSquare
        Rectangle {
            color: "red"
            width: 10
            height: 10
        }
    }
    Loader { sourceComponent: redSquare }
    Loader { sourceComponent: redSquare; x: 20 }
}
					

Notice that while a Rectangle by itself would be automatically rendered and displayed, this is not the case for the above rectangle because it is defined inside a 组件 . The component encapsulates the QML types within, as if they were defined in a separate QML file, and is not loaded until requested (in this case, by the two Loader objects). Because Component is not derived from Item, you cannot anchor anything to it.

定义 组件 is similar to defining a QML 文档 . A QML document has a single top-level item that defines the behavior and properties of that component, and cannot define properties or behavior outside of that top-level item. In the same way, a 组件 definition contains a single top level item (which in the above example is a Rectangle ) and cannot define any data outside of this item, with the exception of an id (which in the above example is redSquare ).

The 组件 type is commonly used to provide graphical components for views. For example, the ListView::delegate property requires a 组件 to specify how each list item is to be displayed.

组件 对象还可以动态创建使用 Qt.createComponent() .

创建上下文

The creation context of a Component corresponds to the context where the Component was declared. This context is used as the parent context (creating a 上下文层次结构 ) when the component is instantiated by an object such as a ListView or a Loader.

在以下范例中， comp1 is created within the root context of MyItem.qml, and any objects instantiated from this component will have access to the ids and properties within that context, such as internalSettings.color 。当 comp1 is used as a ListView delegate in another context (as in main.qml below), it will continue to have access to the properties of its creation context (which would otherwise be private to external users).

Item {
    property Component mycomponent: comp1
    QtObject {
        id: internalSettings
        property color color: "green"
    }
    Component {
        id: comp1
        Rectangle { color: internalSettings.color; width: 400; height: 50 }
    }
}
								

ListView {
    width: 400; height: 400
    model: 5
    delegate: myItem.mycomponent    //will create green Rectangles
    MyItem { id: myItem }
}
								

特性文档编制

The progress of loading the component, from 0.0 (nothing loaded) to 1.0 (finished).

This property holds the status of component loading. The status can be one of the following:

• Component.Null - no data is available for the component
• Component.Ready - the component has been loaded, and can be used to create instances.
• Component.Loading - the component is currently being loaded
• Component.Error - an error occurred while loading the component. Calling errorString() will provide a human-readable description of any errors.

The component URL. This is the URL that was used to construct the component.

附加信号文档编制

Emitted after the object has been instantiated. This can be used to execute script code at startup, once the full QML environment has been established.

相应处理程序是 onCompleted . It can be declared on any object. The order of running the onCompleted handlers is undefined.

Rectangle {
    Component.onCompleted: console.log("Completed Running!")
    Rectangle {
        Component.onCompleted: console.log("Nested Completed Running!")
    }
}
									

Emitted as the object begins destruction. This can be used to undo work done in response to the completed() signal, or other imperative code in your application.

相应处理程序是 onDestruction . It can be declared on any object. The order of running the onDestruction handlers is undefined.

Rectangle {
    Component.onDestruction: console.log("Destruction Beginning!")
    Rectangle {
        Component.onDestruction: console.log("Nested Destruction Beginning!")
    }
}
										

另请参阅 Qt QML .

方法文档编制

Creates and returns an object instance of this component that will have the given parent and properties 。 properties argument is optional. Returns null if object creation fails.

The object will be created in the same context as the one in which the component was created. This function will always return null when called on components which were not created in QML.

If you wish to create an object without setting a parent, specify null 为 parent value. Note that if the returned object is to be displayed, you must provide a valid parent value or set the returned object's parent property, otherwise the object will not be visible.

若 parent is not provided to createObject(), a reference to the returned object must be held so that it is not destroyed by the garbage collector. This is true regardless of whether Item::parent is set afterwards, because setting the Item parent does not change object ownership. Only the graphical parent is changed.

As of QtQuick 1.1 , this method accepts an optional properties argument that specifies a map of initial property values for the created object. These values are applied before the object creation is finalized. This is more efficient than setting property values after object creation, particularly where large sets of property values are defined, and also allows property bindings to be set up (using Qt.binding ) before the object is created.

The properties argument is specified as a map of property-value items. For example, the code below creates an object with initial x and y values of 100 and 100, respectively:

var component = Qt.createComponent("Button.qml");
if (component.status == Component.Ready)
    component.createObject(parent, {"x": 100, "y": 100});
											

可以删除动态创建实例采用 destroy() 方法。见 从 JavaScript 动态创建 QML 对象 了解更多信息。

另请参阅 incubateObject() .

返回任何错误的人类可读描述。

The string includes the file, location, and description of each error. If multiple errors are present, they are separated by a newline character.

If no errors are present, an empty string is returned.

Creates an incubator for an instance of this component. Incubators allow new component instances to be instantiated asynchronously and do not cause freezes in the UI.

The parent argument specifies the parent the created instance will have. Omitting the parameter or passing null will create an object with no parent. In this case, a reference to the created object must be held so that it is not destroyed by the garbage collector.

The properties argument is specified as a map of property-value items which will be set on the created object during its construction. mode may be Qt.Synchronous or Qt.Asynchronous, and controls whether the instance is created synchronously or asynchronously. The default is asynchronous. In some circumstances, even if Qt.Synchronous is specified, the incubator may create the object asynchronously. This happens if the component calling incubateObject() is itself being created asynchronously.

All three arguments are optional.

If successful, the method returns an incubator, otherwise null. The incubator has the following properties:

• status The status of the incubator. Valid values are Component.Ready, Component.Loading and Component.Error.
• object The created object instance. Will only be available once the incubator is in the Ready status.
• onStatusChanged Specifies a callback function to be invoked when the status changes. The status is passed as a parameter to the callback.
• forceCompletion() Call to complete incubation synchronously.

The following example demonstrates how to use an incubator:

var component = Qt.createComponent("Button.qml");
var incubator = component.incubateObject(parent, { x: 10, y: 10 });
if (incubator.status != Component.Ready) {
    incubator.onStatusChanged = function(status) {
        if (status == Component.Ready) {
            print ("Object", incubator.object, "is now ready!");
        }
    }
} else {
    print ("Object", incubator.object, "is ready immediately!");
}
													

可以删除动态创建实例采用 destroy() 方法。见 从 JavaScript 动态创建 QML 对象 了解更多信息。

另请参阅 createObject() .