qml: C++調用qml函數

C++調用qml函數，是通過下面的函數實現的：

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bool QMetaObject::invokeMethod(QObject *obj, const char *member, Qt::ConnectionType type, QGenericReturnArgument ret, 
QGenericArgument val0 = QGenericArgument( Q_NULLPTR ), QGenericArgument val1 = QGenericArgument(), QGenericArgument val2 = QGenericArgument(),
 QGenericArgument val3 = QGenericArgument(), QGenericArgument val4 = QGenericArgument(), QGenericArgument val5 = QGenericArgument(), QGenericArgument val6 = QGenericArgument(),
 QGenericArgument val7 = QGenericArgument(), QGenericArgument val8 = QGenericArgument(), QGenericArgument val9 = QGenericArgument())；

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這里有兩個常用的宏：Q_RETURN_ARG,Q_ARG，從字面意思就可以看出來，一個是用來獲取返回值，另一個用于傳參。 下面是一個例子：

QVariant returnedValue;
QVariant msg = "message sended from C++";
QMetaObject::invokeMethod(pctrlobj, "setTextString", Q_RETURN_ARG(QVariant, returnedValue),Q_ARG(QVariant, msg));

在應用該函數調用qml對象成員前，關鍵是要獲取到要調用的qml對象，有兩種方案可以很方便的獲取到qml對象：

1）? 從qml端直接傳QOBject * 到C++端；

2）? 通過設置objectName,利用findChild()找到對應的對象；

第一種方案就不說了，很簡單實現，這里簡略的講解下第二種方案，? 看下面的例子：

main.qml

import QtQuick 2.9
import QtQuick.Window 2.2
import QtQuick.Controls 1.3
Window {id: windows;visible: truewidth: 640height: 480title: qsTr("Hello World")Button{id: test;width: 70;height: 30;onClicked: test1.open();}Test1{id: test1;visible: false;onShowTest:{}}function  test(){console.log("test ok!");}}

Test1.qml

import QtQuick 2.0
import QtQuick.Window 2.2
import QtQuick.Controls 1.3
Window {id: test;width: 300;height: 200;visible:false;signal  showTest();Button{id: testButton;objectName:"testButton"      //這里設置了對象名稱，用于findChild()獲取對象；text:"click me";onClicked:{showTest();}}function open(){test.visible = true;}function close(){test.visible = false;}}

　　

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QObject>
int main(int argc, char *argv[])
{
#if defined(Q_OS_WIN)QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endifQGuiApplication app(argc, argv);QQmlApplicationEngine engine;engine.load(QUrl(QStringLiteral("qrc:/main.qml")));QObject *pRoot = engine.rootObjects().first();QObject *pButton = pRoot->findChild<QObject *>("testButton");if( pButton ){QObject::connect(pButton,SIGNAL(clicked()),pRoot,SLOT(test()));}if (engine.rootObjects().isEmpty())return -1;return app.exec();
}

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