Custom c++ types exposed to QML

deion

Hi all,

Im my c++ code I have a class AppEngine that has an instance member, userSettings of type UserSettings.
The USerSettings class has Q_PROPERTY -ies like QString serverAddr, etc.
I expose the userSettings object to C++ like this:
In C++:

@ QDeclarativeContext* ctxt = qmlViewer->rootContext(); // qmlViewer is of type QmlApplicationViewer which inherits from QDeclarativeView
ctxt->setContextProperty("userSettings", &this->m_userSettings);
@

In QML I just referenced the userSettings variable and its properties:

@console.log("!!! userSettings: conntype = " + userSettings.connectionType);@

All is well; however I wanted to expose just a single object to QML, in my case the AppEngine object, and access the userSettings from QML using something like appEngine.userSettings.connectionType

For this I declared my UserSettings type as a metaobject, I declared the instance userSettings member as a Q_PROPERTY in AppEngine class; however in QML when I try to access appEngine.userSettings.connectionType the connectionType is 'undefined'; It worked before as I used userSettings directly, without embedding it in appEngine, but I think it's more elegant to have one single root object exposed to QML and sub-objects accessed from this root object.

Below is copy-paste from the relevant code:

UserSettings.h

@
#ifndef USER_SETTINGS_H
#define USER_SETTINGS_H

#include <QObject>
#include <QMetaType>

typedef enum ConnectionType {
CONN_INET = 0,
CONN_BLUETOOTH = 1
} ConnectionType;

class QString;

class UserSettings : public QObject
{
Q_OBJECT
Q_PROPERTY(int connectionType
READ connectionType
WRITE setConnectionType
NOTIFY connectionTypeChanged)
…etc, omitted other properties, post was becoming longer than 6000 chars
friend class AppEngine;

public:
UserSettings();
UserSettings(const UserSettings& settings);
UserSettings& operator=(const UserSettings& settings);
virtual ~UserSettings();
bool operator==(const UserSettings& rhs) const;
bool operator!=(const UserSettings& rhs) const;

// m_connectionType property
void setConnectionType(int aConnectionType) {
    if (m_connectionType != aConnectionType) {
        m_connectionType = (ConnectionType) aConnectionType;
        emit connectionTypeChanged();
    }
}
int connectionType() const {
    return m_connectionType;
}

// m_inetServerAddr property
void setInetServerAddr(const QString &aInetServerAddr) {
    if (m_inetServerAddr != aInetServerAddr) {
        m_inetServerAddr = aInetServerAddr;
        emit inetServerAddrChanged();
    }
}
QString inetServerAddr() const {
    return m_inetServerAddr;
}

// m_tcpPort property
void setTcpPort(int aTcpPort) {
    if (m_tcpPort != aTcpPort) {
        m_tcpPort = aTcpPort;
        emit tcpPortChanged();
    }
}
int tcpPort() const {
    return m_tcpPort;
}

// m_btServerAddr property
void setBtServerAddr(const QString &aBtServerAddr) {
    if (m_btServerAddr != aBtServerAddr) {
        m_btServerAddr = aBtServerAddr;
        emit btServerAddrChanged();
    }
}
QString btServerAddr() const {
    return m_btServerAddr;
}

// m_btServerName property
void setBtServerName(const QString &aBtServerName) {
    if (m_btServerName != aBtServerName) {
        m_btServerName = aBtServerName;
        emit btServerNameChanged();
    }
}
QString btServerName() const {
    return m_btServerName;
}

signals:
void connectionTypeChanged();
void inetServerAddrChanged();
void tcpPortChanged();
void btServerAddrChanged();
void btServerNameChanged();

private:
// Data:
ConnectionType m_connectionType;
QString m_inetServerAddr;
int m_tcpPort;
QString m_btServerAddr;
QString m_btServerName;

private:
static void LoadSettings(UserSettings* settings);
static void SaveSettings(const UserSettings* settings);
};

Q_DECLARE_METATYPE(UserSettings)

#endif//USER_SETTINGS_H
@

AppEngine.h

@
#ifndef APP_ENGINE_H
#define APP_ENGINE_H

#include <QtGui/QApplication>
#include <QCamera>
#include "UserSettings.h"

…etc

class AppEngine : public QApplication
{
Q_OBJECT
Q_PROPERTY(UserSettings userSettings
READ userSettings)

public:
AppEngine(int &argc, char *argv);
virtual ~AppEngine();
void setUpQML(QmlApplicationViewer qmlViewer);
UserSettings userSettings() const;
... etc
private:
// Data:
UserSettings m_userSettings;
...etc
}
@

AppEngine.cpp:
@
AppEngine::AppEngine(int &argc, char **argv):
QApplication(argc, argv),
...etc
{
qRegisterMetaType<UserSettings>();
UserSettings::LoadSettings(&m_userSettings);
...etc
}

void AppEngine::setUpQML(QmlApplicationViewer* qmlViewer)
{
QObject* rootObjMainQml = qmlViewer->rootObject();
QDeclarativeContext* ctxt = qmlViewer->rootContext();
ctxt->setContextProperty("appEngine", this);
...etc
}

UserSettings AppEngine::userSettings() const {
return m_userSettings;
}

@

And in QML (SettingsDlg.qml):
@

function show() {
    console.log("!!! userSettings: conntype = " + appEngine.userSettings.connectionType + "; inetServerAddr=" + appEngine.userSettings.inetServerAddr + "; tcpPort=" + appEngine.userSettings.tcpPort + "; btServerAddr=" + appEngine.userSettings.btServerAddr + "; btServerName=" + appEngine.userSettings.btServerName);
    connTypeList.selectedIdx = -1;

...etc
}
@

And this is what I'm getting in console:
@!!! userSettings: conntype = undefined; inetServerAddr=undefined; tcpPort=undefined; btServerAddr=undefined; btServerName=undefined@

vsorokin

in AppEngine.h
@public:
....
Q_INVOKABLE UserSettings userSettings() const;@

in Qml:
@appEngine.userSettings().connectionType
... etc@

deion

Thanks Vass,

I modified QML:
@console.log("!!! userSettings: conntype = " + appEngine.userSettings().connectionType);@

if in AppEngine.h I keep:

@ Q_PROPERTY(UserSettings userSettings
READ userSettings)
@

and modify the declaration @UserSettings userSettings() const;@ to @Q_INVOKABLE UserSettings userSettings() const;@
I get the following error at run-time:
TypeError: Result of expression 'appEngine.userSettings' [QVariant(UserSettings)] is not a function.

If I remove in AppEngine.h:
@ Q_PROPERTY(UserSettings userSettings
READ userSettings)
@
and keep only @Q_INVOKABLE UserSettings userSettings() const;@

I get the following:
!!! userSettings: conntype = undefined

Getting closer to resolving this, but not yet :D

Thanks,
Ionut

chriadam

UserSettings derives from QObject? Then you want your property type (or invokable function return type) to be a UserSettings pointer. Passing a QObject in a QVariant (and between QML and C++, all types are marshalled into QVariants) probably isn't going to work as you hope.

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Custom c++ types exposed to QML