QML 中的附加属性

Posted 2023-02-16

【中文标题】QML 中的附加属性

【英文标题】：Attached properties in QML

【发布时间】：2013-01-26 13:02:46

【问题描述】：

我可以为像组件这样的所有属性创建自己的附件吗？

Item
    Component.onCompleted :  // Component is attached to everyone Items

【问题讨论】：

是的，请参阅：qt-project.org/doc/qt-4.8/…

是的，通过它我可以将属性附加到我自己的对象上，但我需要的是从图像、项目或矩形等标准对象中调用这些属性

也感兴趣：Are custom attached properties possible in QML?

【参考方案1】：

您可能无法将属性附加到不是您创建的项目或组件。但是你为什么要这样做呢？

相反，您可以考虑使用信号和全局属性。

对于您可以从任何地方访问的全局属性，您可以设置声明性视图的根上下文的上下文属性。。 p>

即，

QmlApplicationViewer viewer;
MyPropertyClass myProp;
viewer->rootContext()->setContextProperty("MyPropClass", &myProp);

现在，在您的 QML 文件中，您可以访问此类的属性

Rectangle 
    Text 
        text: MyPropClass.getMyPropText()
    
    MouseArea 
        onClicked:  MyPropClass.text = "Clicked" 
    

这将从 MyPropertyClass 调用 Q_INVOKABLE 方法 getMyPropText()。并且可以在发出某些信号时设置 Q_PROPERTY 'text'。

你需要这件衣服吗？

【参考方案2】：

是的，例如：

#include <QQmlEngine>
#include <QTimer>

class TestAttached : public QObject

    Q_OBJECT
    // Declare property with setter and getter
    Q_PROPERTY(int val READ getVal WRITE setVal)
public:
    TestAttached() Q_DECL_EQ_DEFAULT;
    explicit TestAttached(QObject *parent):
        QObjectparent,
        m_val100500
    
        Q_ASSERT(parent);
        qDebug() << "* We just have created the object of attached properties for" << parent->metaObject()->className();
    
    ~TestAttached() Q_DECL_EQ_DEFAULT;
    
    // define static function qmlAttachedProperties(QObject *object)
    // which returns pointer to instance of TestAttached class
    static TestAttached *qmlAttachedProperties(QObject *object)
    
        TestAttached* testAttached  new TestAttachedobject ;
        QTimer* timer  new QTimertestAttached ;
        connect(timer, &QTimer::timeout,
        [testAttached] 
            testAttached->setVal(testAttached->getVal()+1);
            emit testAttached->testDone(testAttached->getVal());
        );
        timer->start(3000);
        return testAttached;
    

    inline int getVal() const
    
        return m_val;
    
    inline void setVal(int val)
    
        m_val = val;
    

signals:
    void testDone(int val);

private:
    int m_val;
;
// Makes the type TestAttached known to QMetaType (for using with QVariant)
QML_DECLARE_TYPE(TestAttached)
// declares that the TestAttached supports attached properties.
QML_DECLARE_TYPEINFO(TestAttached, QML_HAS_ATTACHED_PROPERTIES)

在 QML 系统中注册附加类型（例如main.cpp）：

qmlRegisterUncreatableType<TestAttached>("my.test", 1, 0, "Test", QObject::tr("Test is an abstract type that is only available as an attached property."));

然后在main.qml试试：

import QtQuick 2.15
import QtQuick.Window 2.15
//import our module
import my.test 1.0

Window 
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World of Attached properties")

    Rectangle 
        color: focus ? Qt.lighter("red") : "red"
        width: parent.width/2; height: parent.height
        anchors.left: parent.left
        Component.onCompleted: 
            console.log("Rectangle is completed", Test.val)
        
        Keys.onReturnPressed: 
            console.log("Rect 1: Attachet value is", Test.val)
        

        Test.val: 20000

        Test.onTestDone: function(num) 
            console.log("We received", num, "from attached object")
        

        MouseArea 
            anchors.fill: parent
            onClicked: parent.focus = true
        
    

    Rectangle 
        color: focus ? Qt.lighter("blue") : "blue"
        width: parent.width/2; height: parent.height
        anchors.right: parent.right
        focus: true

        Keys.onReturnPressed: 
            // The attached object will created after return pressed
            console.log("Rect 2: Attachet value is", Test.val)
        

        MouseArea 
            anchors.fill: parent
            onClicked: parent.focus = true