从QML代码调用C++函数

Question

我想从QML代码中调用一个c++函数

例如，在下面的代码中，我有一个有2个输入的窗口：数量和价格我想调用一个c++函数来评估小计并向其添加5%的税。

我试过搜索很多地方，但无法获得最新版本的QT5的完整工作代码。请告诉我如何从QML调用C++函数。

main.qml:

import QtQuick 2.2
import QtQuick.Controls 1.1
ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    menuBar: MenuBar {
        Menu {
            title: qsTr("File")
            MenuItem {
                text: qsTr("Exit")
                onTriggered: Qt.quit();
            }
        }
    }
    Column{
        Label {
            text: qsTr("Enter the number of items purchased: ")
        }
        TextField {
            id: in1
            objectName: "in1"
        }
        Label {
            text: qsTr("Enter the price per item ($):")
        }
        TextField {
            id: in2
            objectName: "in2"
        }
        Button {
            id: button
            objectName: "button"
            text: "Compute"
            onClicked: {
                total.text = "Final bill, including 5% tax, is $" + clickedButton(in1.text, in2.text); // here i'm calling the c++ function
            }
        }
        Label {
            id: total
            objectName: "total"
            text: "Final bill, including 5% tax, is $____"
        }
    }
}

main.cpp

#include <QApplication>
#include <QQmlApplicationEngine>
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
    return app.exec();
}
double clickedButton(int number, int price){
    const double TAX_rate = 0.05;
    double subtotal;
    subtotal = price*number;
    return (subtotal + subtotal*TAX_rate);
}

Answer 1

创建一个类，如：

class BillCalculator : public QObject
{
   Q_OBJECT
   Q_PROPERTY(double totalPrice READ totalPrice WRITE setTotalPrice NOTIFY totalPriceChanged)
public:
   BillCalculator(QObject *parent = 0) :
     QObject(parent),
    mTotalPrice(0.0)
   {
   }
   double totalPrice() const { return mTotalPrice; }
signals:
   void totalPriceChanged();
public slots: 
   void setTotalPrice(const double &arg) 
   {
     if(mTotalPrice != arg)
     {
       mTotalPrice = arg;
       emit totalPriceChanged();
     }
   }
   void calculateTotalPrice(int number, int price)
   {
    const double TAX_rate = 0.05;
    double subtotal;
    subtotal = price*number;
    setTotalPrice(subtotal + subtotal*TAX_rate);
   }
protected:
   double mTotalPrice;
};

在你的main.cpp中，包括<QQmlContext>并修改如下

  QQmlApplicationEngine engine;
  engine.rootContext()->setContextProperty("billCalculator", new BillCalculator);
  engine.load(QUrl(QStringLiteral("qrc:///main.qml")));

修改你的main.qml文件如下

   Button {
            id: button
            objectName: "button"
            text: "Compute"
            onClicked: {
                billCalculator.calculateTotalPrice(parseInt(in1.text), parseInt(in2.text));
            }
        }
        Label {
            id: total
            objectName: "total"
            text: "Final bill, including 5% tax, is $" + (billCalculator.totalPrice > 0 ? billCalculator.totalPrice.toFixed(2) : "____")
        }

Answer 2

您需要将clickedButton声明为Q_INVOKABLE，如下所示：

 public:
 Q_INVOKABLE void cppMethod(const QString &msg) {
     qDebug() << "Called the C++ method with" << msg;
 }

请参阅此示例：http://qt-project.org/doc/qt-4.8/qtbinding.html

Answer 3

简单使用：

engine.rootContext()->setContextProperty("yourName", new yourClass());

在qml中，您可以使用yourname.yourfunction()调用函数另外，在您的类中，您必须使函数Q_INVOKABEL