【qml学习笔记】QML与C++的交互

QML与C++的交互

在QML中访问c++对象

• 首先创建一个类，这个类需继承自QObject，必须有Q_OBJECT宏,并加入QML_ELEMENT宏，并且私有成员具有Q_PROPERTY宏（可通过ALT+ENTER快速设置）

#include <QObject>
#include <QtQml>//注意 QML_ELEMENT 需要该头文件
class MyCppObj : public QObject
{Q_OBJECTQML_ELEMENT
public:explicit MyCppObj(QObject *parent = nullptr);int iValue() const;void setIValue(int newIValue);QString string() const;void setString(const QString &newString);//加入 Q_INVOKABLE宏的函数才可在QML端进行访问Q_INVOKABLE void func();private:int m_iValue;QString m_string;Q_PROPERTY(int iValue READ iValue WRITE setIValue NOTIFY iValueChanged FINAL)Q_PROPERTY(QString string READ string WRITE setString NOTIFY stringChanged FINAL)signals:void iValueChanged();void stringChanged();
};

• 在cpp文件中对对象进行注册

//一定要通过创建对象来定义我们自定义的obj，对象存在于qml端
qmlRegisterType<MyCppObj>("MyCppObj.Obj",1,0,"MyCppObj");
//MyCppObj.Obj:import的库的名字
//1：主版本号
//0：次版本号
//MyCppObj：QML中类的名字

• 在qml文件中导入即可使用

import QtQuick 2.15
import QtQuick.Window 2.15
import MyCppObj 1.0
Window {width: 640height: 480visible: trueMyCppObj{id:myObjonIValueChanged: {}onSstringChanged: {}}Component.onCompleted:{console.log(myObj.iValue,myObj.sstring)myObj.func()}
}

QML端信号绑定到C++端(在qml端进行连接)

在以上内容的基础上即完成c++类的注册之后

• 声明槽函数：

public slots:void cppSlot(int i,QString s){qDebug()<<__FUNCTION__<<i<<s;}

• 在QML中进行连接

Window {id:windowwidth: 640height: 480visible: truesignal qmlSignal(int i,string s)MyCppObj{id:myObjonIValueChanged: {}onSstringChanged: {}}Button{onClicked:{qmlSignal(10,"666")}}Connections{target: windowfunction onQmlSignal(i,s){myObj.cppSlot(i,s);}}
}

• 另一种连接方法

Component.onCompleted:{qmlSignal.connect(myObj.cppSlot)}

在C++端进行连接

engine.load(url);
auto list = engine.rootObjects();//在engine.load之后
auto window = list.first();
MyCppObj *myObj = new MyCppObj();QObject::connect(window,SIGNAL(qmlSignal(int,QString)),myObj,SLOT(cppSlot(int,QString)));

C++端信号绑定到QML端

• 在qml端进行绑定

 Button{onClicked:{myObj.cppSignal(10,"6")}}function qmlSlot(i,s){console.log("qml",i,s)}Connections{target: myObjfunction onCppSignal(i,s){qmlSlot(i,s);}}

• 在c++端进行连接

注意收发双方参数都应该是QVariant类型

QObject::connect(myObj,SIGNAL(cppSignal(QVariant,QVariant)),window,SLOT(qmlSlot(QVariant,QVariant)));

注册单例类

当我们使用qmlRegisterType时，要通过创建对象来定义我们自定义的obj，对象存在于qml端，当我们需要类存在于全局时可使用qmlRegisterSingletonInstance

 MyCppObj *myObj = new MyCppObj();qmlRegisterSingletonInstance("MyCppObjSingle",1,0,"MyCppObj",myObj);

C++端调用QML端函数

• 获取qml对象

auto list = engine.rootObjects();auto window = list.first();

• 准备返回值和参数

 QVariant res;QVariant arg_1 = 123;QVariant arg_2 = "ffffff";

• 通过QMetaObject::invokeMethod调用

QMetaObject::invokeMethod(window,//获取到的qml对象"qmlFunc",//需要调用的函数名Q_RETURN_ARG(QVariant,res),//准备好的返回值和参数Q_ARG(QVariant,arg_1),Q_ARG(QVariant,arg_2));