Question

我从.ini文件读取到c ++中的整数，然后通过绑定在QML中使用。在运行时，可以更改.ini文件中的值，这会导致c ++整数也被更改。我发现尽管整数确实在c ++中发生了变化（通过qDebug（）验证），但QML中的绑定值并没有发生变化，尽管发出了所需的changed（）信号。我的申请结构摘录如下：

main.cpp中：

//Establish the QQmlApplication engine, set context properties for the two c++ files and load the QML file.

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

maincpp.h：

public:
    explicit MainCpp(QObject *parent = nullptr);

    Q_PROPERTY(int someValue READ someValue NOTIFY someValueChanged)
    int someValue(){return m_someValue;}

signals:
    void someValueChanged();

private:
    int    m_someValue;

的config.h：

public:
    explicit Config(QObject *parent = nullptr);

    Q_PROPERTY(int someOtherValue READ someOtherValue NOTIFY someOtheralueChanged)
    int someOtherValue(){return m_someOtherValue;}

signals:
    void someOtherValueChanged();

public:
    void loadSettings();

public:
    int      m_someOtherValue;
    QString  m_File;

config.cpp：

Config::Config(QObject *parent) : QObject(parent)
{
    m_File = "/some/path/to/settings/file/config.ini";
    loadSettings();
}

void Config::loadSettings()
{
    QSettings settings(m_File, QSettings::IniFormat);
    settings.beginGroup("GROUP_NAME");
    m_someOtherValue = settings.value("someOtherValueConfig", "").toInt();
    settings.endGroup();
}

maincpp.cpp：

MainCpp::MainCpp(QObject *parent = nullptr) : QObject(parent)
{
    Config configPointer;
    m_someValue = configPointer.someOtherValue();
    emit someValueChanged();
}

main.qml：

Window {
    width: 800
    height: 480

    Text {
        id: someText
        text: Config.someOtherValue //This does NOT update on changes to m_someOtherValue on the c++ side
        //text: MainCpp.someValue //This DOES update on change to m_someValue on the c++ side
    }
}

在maincpp.cpp中调用以下代码来更新.ini文件：

void MainCpp::update(int var)
{
    Config configPointer;

    QSettings settings("/some/path/to/settings/file/config.ini", QSettings::IniFormat);
    settings.setValue("GROUP_NAME/someOtherValueConfig", var);
    configPointer.m_someOtherValue = var;
    m_someValue = configPointer.someOtherValue;
    emit configPointer.someOtherValueChanged();
    emit someValueChanged();
}

我已经添加了#OtherValueChanged（）＆＃39;信号无济于事。如前所述，我知道m_someOtherValue已经改变，因为我使用qDebug（）查询它。如果m_someValue发生变化，为什么QML没有观察到m_someOtherValue的变化？

Answer 1

导致该行为是因为您有3个Config对象：

的main.cpp

engine.rootContext()->setContextProperty(QStringLiteral("Config"), new Config());

MainCpp构造函数：

MainCpp::MainCpp(QObject *parent = nullptr) : QObject(parent)
{
    Config configPointer; 
    [...]

更新方法：

void MainCpp::update(int var)
{
    Config configPointer;

也就是说，如果其中一些更改不会更改其他对象，因为它们不同。

一种可能的解决方案是使Config成为Singleton，因此整个应用程序中的所有对象都是相同的。

<强>的config.h

#ifndef CONFIG_H
#define CONFIG_H

#include <QObject>
#include <QSettings>

class Config : public QObject
{
    static Config* instance;
    Q_OBJECT
    Q_PROPERTY(int someOtherValue READ someOtherValue NOTIFY someOtherValueChanged)
    explicit Config(QObject *parent = nullptr);

public:
    static Config *getInstance();
    int someOtherValue(){return m_someOtherValue;}
    [...]

};

#endif // CONFIG_H

<强> config.cpp

#include "config.h"

Config* Config::instance = 0;

Config::Config(QObject *parent):QObject(parent){
    m_File = "/some/path/to/settings/file/config.ini";
    loadSettings();
}

Config *Config::getInstance(){
    if (instance == 0)
        instance = new Config;
    return instance;
}

void Config::loadSettings(){
    [...]
}

然后通过getInstance（）访问该对象：

<强> maincpp.cpp

#include "maincpp.h"

MainCpp::MainCpp(QObject *parent):QObject(parent){
    Config *configPointer = Config::getInstance();
    m_someValue = configPointer->someOtherValue();
    emit someValueChanged();
}

void MainCpp::update(int var)
{
    Config *configPointer = Config::getInstance();
    QSettings settings("/some/path/to/settings/file/config.ini", QSettings::IniFormat);
    settings.setValue("GROUP_NAME/someOtherValueConfig", var);
    configPointer->m_someOtherValue = var;
    m_someValue = configPointer->someOtherValue();
    emit configPointer->someOtherValueChanged();
    emit someValueChanged();
}

要在QML中使用它，您必须在qmlRegisterSingletonType()：

<强>的main.cpp

#include "maincpp.h"

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

static QObject *singletonTypeProvider(QQmlEngine *, QJSEngine *)
{
    return Config::getInstance();
}

int main(int argc, char *argv[])
{
#if defined(Q_OS_WIN)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

    QGuiApplication app(argc, argv);
    qmlRegisterSingletonType<Config>("Config", 1, 0, "Config", singletonTypeProvider);

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty(QStringLiteral("MainCpp"), new MainCpp());
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

在qml中，您必须导入模块并使用对象：

import QtQuick 2.9
import QtQuick.Window 2.2
import QtQuick.Controls 1.4
import QtQuick.Layouts 1.3

import Config 1.0

Window {
    width: 800
    height: 480
    visible: true

    ColumnLayout{

        Text {
            id: someText
            text: Config.someOtherValue
        }
        Text {
            id: anotherText
            text: MainCpp.someValue
        }

        Slider {
            value: 0.5
            maximumValue: 100
            onValueChanged: MainCpp.update(value)
        }
    }
}

完整示例可在以下link中找到。

绑定的c ++值未在QML

1 个答案: