如何将QObject指针的属性公开给QML

时间：2015-07-16 05:43:15

标签： qt qml qtquick2 qproperty

我正在对我的班级进行非常简短（和部分）的描述以显示我的问题。基本上我已经设置了两个属性。

class Fruit : public QObject
{
Q_OBJECT
  ....
public:
    Q_PROPERTY( int price READ getPrice NOTIFY priceChanged)

    Q_PROPERTY(Fruit * fruit READ fruit WRITE setFruit NOTIFY fruitChanged)
}

在我的QML中，如果我访问price属性，它运行良好。但是，如果我访问显然返回fruit的{​​{1}}属性，然后尝试使用其Fruit属性，那么这不起作用。这不应该以这种方式工作吗？

price

第二个返回Text { id: myText anchors.centerIn: parent text: basket.price // shows correctly //text: basket.fruit.price // doesn't show } ，它也是一个属性，它有Fruit属性，但它似乎无法访问该属性？这有用吗？

已更新

我包含了我的源代码。我用price创建了一个新的演示，这种方式更有意义。我试着根据收到的答案让它工作但没有运气。

HardwareComponent类是HardwareComponent和Computer的基类。

的main.cpp 

CPU

main.qml 

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

class HardwareComponent : public QObject
{
   Q_OBJECT
public:
   HardwareComponent() : m_price(0) {}
   virtual int price() = 0;
   virtual Q_INVOKABLE void add(HardwareComponent * item) { m_CPU = item; }
   HardwareComponent * getCPU() const { return m_CPU; }

   Q_SLOT virtual void setPrice(int arg)
   {
      if (m_price == arg) return;
      m_price = arg;
      emit priceChanged(arg);
   }
   Q_SIGNAL void priceChanged(int arg);

protected:
   Q_PROPERTY(HardwareComponent * cpu READ getCPU);
   Q_PROPERTY(int price READ price WRITE setPrice NOTIFY priceChanged)

   HardwareComponent * m_CPU;
   int m_price;
};

class Computer : public HardwareComponent
{
   Q_OBJECT
public:
   Computer() { m_price = 500; }

   int price() { return m_price; }
   void setprice(int arg) { m_price = arg; }
};

class CPU : public HardwareComponent
{
   Q_OBJECT
public:
   CPU() { m_price = 100; }

   int price() { return m_price; }
   void setprice(int arg) { m_price = arg; }
};

int main(int argc, char *argv[])
{
   HardwareComponent * computer = new Computer;
   CPU * cpu = new CPU;
   computer->add( cpu );

   QGuiApplication app(argc, argv);
   QQmlApplicationEngine engine;

   engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
   engine.rootContext()->setContextProperty("computer", computer); 

   return app.exec();
}

#include "main.moc"

这是我所有项目文件的完整源代码。

当我运行它时，我得到了这个输出：

  

启动C：\ Users \ User \ Documents \ My Qt   项目\集结硬件Desktop_Qt_5_4_0_MSVC2010_OpenGL_32bit-调试\调试\ hardware.exe ...   启用QML调试。只能在安全的环境中使用它。   qrc：/MainForm.ui.qml：20：ReferenceError：未定义计算机

即使它在第20行（computer.price）行发出警告，它仍然可以工作并显示计算机的价格（= 500）。如果更改import QtQuick 2.3 import QtQuick.Window 2.2 Window { visible: true width: 360 height: 360 Text { anchors.centerIn: parent text: computer.price // works //text: computer.cpu.price // doesn't work, doesn't show any value } } ，则会报告相同的警告，但价格不再显示 - 它似乎无法正常工作。

问题是因为价格是虚拟财产，它有效！但如果我在计算机组件内的另一个硬件组件上使用此属性，它就不起作用！ Mido发布的代码/答案让我希望有一个解决方案，它看起来非常接近！我希望我能做到这一点。

2 个答案:

答案 0 :(得分：2)

我在您的示例中创建了一个Fruit类，但它工作正常。我创建了Fruit的新实例，我可以获得price值。这是我的代码：

fruit.h 

#ifndef FRUIT_H
#define FRUIT_H

#include <QObject>
#include <QQuickView>

class Fruit : public QObject
{
    Q_OBJECT
    Q_PROPERTY( int price READ getPrice WRITE setPrice  NOTIFY priceChanged)
    Q_PROPERTY(Fruit * fruit READ fruit WRITE setFruit NOTIFY fruitChanged)

public:
    Fruit();
    ~Fruit();
    Fruit *fruit();
    void setFruit(Fruit * value);
    int getPrice();
    void setPrice(int value);

signals:
    void fruitChanged();
    void priceChanged(int price);

private:
    int _price;
    Fruit *_fruit;
};

#endif // FRUIT_H

fruit.cpp 

#include "fruit.h"

Fruit::Fruit() :
    _price(1),_fruit(this)
{
}

Fruit::~Fruit()
{
    if(_fruit)
    {
        delete _fruit;
        _fruit = NULL;
    }
}

Fruit *Fruit::fruit()
{
    //Uncomment this line to test the set
    //_fruit = new Fruit;
    return _fruit;
}

void Fruit::setFruit(Fruit *value)
{
    _fruit = value;
    emit fruitChanged();
}

int Fruit::getPrice()
{
    return _price;
}

void Fruit::setPrice(int value)
{
    _price = value;
    emit priceChanged(_price);
}

的main.cpp 

#include <QGuiApplication>
#include <QQuickView>
#include <QQmlContext>
#include "fruit.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQuickView view;
    view.rootContext()->setContextProperty("basket", new Fruit);
    view.setSource(QStringLiteral("qml/main.qml"));
    view.show();
    return app.exec();
}

main.qml 

import QtQuick 2.2

Rectangle {
    width:800
    height: 480
    property var obj
    color: "yellow"

    Text{
        text: basket.fruit.price
        font.pixelSize: 20
    }

    Component.onCompleted: {
        basket.price = 20
        console.log(basket.fruit.price)
    }
}

答案 1 :(得分：2)

只有一些错误，特别是与QML相关：

  1. 必须在引擎加载qml文件之前设置上下文属性。

  2. 您尚未注册HardwareComponent类型。有关详细信息，请参阅Defining QML Types from C++。

    3. 除了QML方面，您似乎希望硬件是具有树结构的复合材料。由于QObject已经是复合词，因此您可以利用此优势。硬件项目树可以是对象树。添加或删除子项时，QObject会通知父母：因此，在添加和删除子项时，可以很容易地保持价格最新。

    每个组件都有unitPrice：这是隔离组件的价格。 price是组件单价的总和，以及其子级的价格。

    您可以缓存它并仅在单位价格更改或子价格更改时更新它，而不是遍历整个树以获取总价格。类似地，当前的CPU可以被缓存，您可以在任何给定的时间强制执行单个CPU，等等。该示例是功能性的，但只有最小的草图。

    我还展示了如何更改计算机中的CPU类型。有价格变化和CPU变化的通知。当cpu属性发生变化时，以及任何price属性发生变化时，QML UI会做出适当的反应。

    screenshot of the example

    的main.cpp 

    #include <QGuiApplication>
#include <QtQml>

class HardwareComponent : public QObject {
   Q_OBJECT
   Q_PROPERTY(QString category MEMBER m_category READ category CONSTANT)
   Q_PROPERTY(HardwareComponent * cpu READ cpu WRITE setCpu NOTIFY cpuChanged)
   Q_PROPERTY(int price READ price NOTIFY priceChanged)
   Q_PROPERTY(int unitPrice MEMBER m_unitPrice READ unitPrice WRITE setUnitPrice NOTIFY unitPriceChanged)
   QString m_category;
   int m_unitPrice;
   bool event(QEvent * ev) Q_DECL_OVERRIDE {
      if (ev->type() != QEvent::ChildAdded && ev->type() != QEvent::ChildRemoved)
         return QObject::event(ev);
      auto childEvent = static_cast<QChildEvent*>(ev);
      auto child = qobject_cast<HardwareComponent*>(childEvent->child());
      if (! child) return QObject::event(ev);
      if (childEvent->added())
         connect(child, &HardwareComponent::priceChanged,
                 this, &HardwareComponent::priceChanged, Qt::UniqueConnection);
      else
         disconnect(child, &HardwareComponent::priceChanged,
                    this, &HardwareComponent::priceChanged);
      emit priceChanged(price());
      if (child->category() == "CPU") emit cpuChanged(cpu());
      return QObject::event(ev);
   }
public:
   HardwareComponent(int price, QString category = QString(), QObject * parent = 0) :
      QObject(parent), m_category(category), m_unitPrice(price) {}
   HardwareComponent * cpu() const {
      for (auto child : findChildren<HardwareComponent*>())
         if (child->category() == "CPU") return child;
      return 0;
   }
   Q_INVOKABLE void setCpu(HardwareComponent * newCpu) {
      Q_ASSERT(!newCpu || newCpu->category() == "CPU");
      auto oldCpu = cpu();
      if (oldCpu == newCpu) return;
      if (oldCpu) oldCpu->setParent(0);
      if (newCpu) newCpu->setParent(this);
      emit cpuChanged(newCpu);
   }
   Q_SIGNAL void cpuChanged(HardwareComponent *);
   virtual int price() const {
      int total = unitPrice();
      for (auto child : findChildren<HardwareComponent*>(QString(), Qt::FindDirectChildrenOnly))
         total += child->price();
      return total;
   }
   Q_SIGNAL void priceChanged(int);
   int unitPrice() const { return m_unitPrice; }
   void setUnitPrice(int unitPrice) {
      if (m_unitPrice == unitPrice) return;
      m_unitPrice = unitPrice;
      emit unitPriceChanged(m_unitPrice);
      emit priceChanged(this->price());
   }
   Q_SIGNAL void unitPriceChanged(int);
   QString category() const { return m_category; }
};

struct Computer : public HardwareComponent {
   Computer() : HardwareComponent(400) {}
};

class FluctuatingPriceComponent : public HardwareComponent {
   QTimer m_timer;
   int m_basePrice;
public:
   FluctuatingPriceComponent(int basePrice, const QString & category = QString(), QObject * parent = 0) :
      HardwareComponent(basePrice, category, parent),
      m_basePrice(basePrice) {
      m_timer.start(250);
      connect(&m_timer, &QTimer::timeout, [this]{
         setUnitPrice(m_basePrice + qrand()*20.0/RAND_MAX - 10);
      });
   }
};

int main(int argc, char *argv[])
{
   QGuiApplication app(argc, argv);
   QQmlApplicationEngine engine;
   Computer computer;
   HardwareComponent memoryBay(40, "Memory Bay", &computer);
   HardwareComponent memoryStick(60, "Memory Stick", &memoryBay);
   FluctuatingPriceComponent cpu1(100, "CPU", &computer);
   HardwareComponent cpu2(200, "CPU");

   qmlRegisterUncreatableType<HardwareComponent>("bar.foo", 1, 0, "HardwareComponent", "");
   engine.rootContext()->setContextProperty("computer", &computer);
   engine.rootContext()->setContextProperty("cpu1", &cpu1);
   engine.rootContext()->setContextProperty("cpu2", &cpu2);
   engine.load(QUrl("qrc:/main.qml"));
   return app.exec();
}

#include "main.moc"

    main.qml 

    import QtQuick 2.0
import QtQuick.Controls 1.2
import QtQuick.Window 2.0

Window {
    visible: true
    Column {
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.verticalCenter: parent.verticalCenter
        Text {
            text: "Computer price: " + computer.price
        }
        Text {
            text: "CPU price: " + (computer.cpu ? computer.cpu.price : "N/A")
        }
        Button {
            text: "Use CPU 1";
            onClicked: { computer.setCpu(cpu1) }
        }
        Button {
            text: "Use CPU 2";
            onClicked: { computer.setCpu(cpu2) }
        }
        Button {
            text: "Use no CPU";
            onClicked: { computer.setCpu(undefined) }
        }
    }
}
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