Qt注册类对象单例与单类型区别

1.实现类型SingletonTypeExample

#ifndef SINGLETONTYPEEXAMPLE_H
#define SINGLETONTYPEEXAMPLE_H

#include <QObject>

class SingletonTypeExample : public QObject
{
    Q_OBJECT
public:
    //只能显示构造类对象
    explicit SingletonTypeExample(QObject *parent = nullptr);
    //属性
    Q_PROPERTY (int    someProperty
                READ   someProperty           //读取属性值
                WRITE  setSomeProperty       //设置属性值
                NOTIFY somePropertyChanged) //属性值变更通知

public:
    //析构
    ~SingletonTypeExample(){};
    //QML前端可直接调用方法
    Q_INVOKABLE int doSomething() {
        setSomeProperty(5);
        return m_someProperty;
    }
    //获取属性值
    int someProperty() const {
        return m_someProperty;
    }
    //设置属性值
    void setSomeProperty(int val) {
        m_someProperty = val;//属性值
        emit somePropertyChanged(val);//发射属性变更信号
    }

signals:
    void somePropertyChanged(int newValue);//属性变更信号声明

private:
    int m_someProperty;//私有属性值
};

#endif // SINGLETONTYPEEXAMPLE_H

#include "singletontypeexample.h"
//构造实现
SingletonTypeExample::SingletonTypeExample(QObject *parent)
    : QObject{parent}, m_someProperty(0) //初始化属性变量
{

}

 2.创建类对象静态实例,已为下面注册用

//注册类对象为单类型
static QObject *QObjectSingletonTypeProvider(QQmlEngine *engine, QJSEngine *scriptEngine){
    Q_UNUSED(engine)
    Q_UNUSED(scriptEngine)
    SingletonTypeExample *st = new SingletonTypeExample();//实例化类对象并返回该对象
    return st;
}

因为注册函数要求包含QQmlEngine *engine, QJSEngine *scriptEngine这两个参数  

 

3.注册单类型 

//注册类对象单类型
    qmlRegisterSingletonType<SingletonTypeExample>("Qt.jsApi.QObjectSingleton", 1, 0, "MyApi",QObjectSingletonTypeProvider );

4.在QML中使用单类型

上面为注册类对象为单类型使用

下面演示注册类对象为单例使用

1.创建类型MySysInfo

#ifndef MYSYSINFO_H
#define MYSYSINFO_H

#include <QObject>
#include <QQuickItem>
#include <QSysInfo>

class MySysInfo : public QObject
{
    Q_OBJECT
public:
    explicit MySysInfo(QObject *parent = nullptr);
    //productType
    Q_INVOKABLE QString getSysProductType();
    //productVersion
    Q_INVOKABLE QString getSysProductVersion();
    //currentCpuArchitecture
    Q_INVOKABLE QString getSysCurrentCpuArchitecture();
signals:

};

#endif // MYSYSINFO_H

 

#include "mysysinfo.h"

MySysInfo::MySysInfo(QObject *parent)
    : QObject{parent}
{

}

QString MySysInfo::getSysProductType()
{
    return QString( QSysInfo::productType().toStdString().c_str());
}

QString MySysInfo::getSysProductVersion()
{
    return QSysInfo::productVersion();
}

QString MySysInfo::getSysCurrentCpuArchitecture()
{
    return QSysInfo::currentCpuArchitecture();
}

2.注册MySysInfo为单例

//注册单例
    MySysInfo *_info = new MySysInfo();
    qmlRegisterSingletonInstance<MySysInfo>("App.SysInfo",1,0,"SysInfo",_info);

3.在QML中使用单例

上面为注册C++类对象为单类型与单例使用

下面注册JS单例并使用

1.创建JS静态单类型

//首先,定义单类型提供函数(回调).
static QJSValue jsSingleTypeProvider(QQmlEngine *engine, QJSEngine *jsEngine){
    Q_UNUSED(engine)

    static int val = 5;
    QJSValue singleType = jsEngine->newObject();
    singleType.setProperty("propertyOfSingleType", val++);
    return singleType;
}

JS注册单类型函数要求提供一个包含QQmlEngine *engine, QJSEngine *jsEngine这两个参数 并返回QJSValue类型的静态对象 

 

 2.注册JS单类型

//其次,注册js单例函数给qml调用
    qmlRegisterSingletonType("Qt.jsApi", 1, 0, "JsApi", jsSingleTypeProvider);

3.在QML中使用JS注册单类型

4.直接使用Lambda注册JS单类型

//直接使用Lambda表达式注册
    qmlRegisterSingletonType("Qt.jsApi.Ext", 1, 0, "JsApiExt", [](QQmlEngine *engine, QJSEngine *jsEngine) -> QJSValue {
        Q_UNUSED(engine)
        static QString strVal = "HelloWorld";
        QJSValue obj = jsEngine->newObject();
        obj.setProperty("propertyOfJsApiWithString", strVal);
        return obj;
    });

 5.在QML中使用