Send QJsonObject from plugin to main app

[fem_dev]

Hi, I have a main application that will load many future developed plugins with the same interface:

#ifndef PLUGIN_API_H
#define PLUGIN_API_H

#include <QString>
#include <QDebug>

class Plugin_API
{
public:
    virtual ~Plugin_API() = default;

    virtual QJsonObject data_from_plugin2app(void) = 0;
    virtual void open_ui(const int id) = 0;
    virtual void run(const int id) = 0;
};

// Declare our interface:
Q_DECLARE_INTERFACE(Plugin_API, "com.lamar.plugin")

#endif // PLUGIN_H

The loaded plugins will be placed by the user in a custom serial sequence of execution.

Now I can call the plugin->open_ui() and I get the plugin GUI on my screen. So I can fill the plugin input text with some data.

My problem is:
I have to save this plugin data (QJsonObject) in a main QJsonArray plugins_data that is a variable located in the main application.

How can I send the data from my plugin (*.dll) to my main application?

[fem_dev]

Thank you @SGaist and @jsulm
With your help I think that I found a solution! Here is the code:

My plugin interface is called Plugin_API. So the plugin_api.h is:

#ifndef PLUGIN_API_H
#define PLUGIN_API_H

#include <QString>
#include <QDebug>
#include <QJsonObject>
#include <QObject>

// You have to import and inherit QOBject in the plugin interface
class Plugin_API : public QObject
{
    // USE Q_OBJECT MACRO inside the interface
    Q_OBJECT
public:
    virtual ~Plugin_API() = default;

    virtual QJsonObject get_data(void) = 0;
    virtual void set_project_path(const QString project_path) = 0;
    virtual void open_ui(const QJsonObject ui_data) = 0;
    virtual void run(const int job_id) = 0;

    // ===== SIGNALS ===== //
    // You have to declare the signals in the interface too:
    virtual void send_msg(const QString msg) = 0;
};

// Declare our interface:
Q_DECLARE_INTERFACE(Plugin_API, "com.lamar.plugin")

#endif // PLUGIN_API_H

After that, in the plugin.h I have:

// Do NOT inherit plublic QObject here:
class PLUGINSHARED_EXPORT Plugin: public Plugin_API
{
    // ADD Q_OBJECT MACRO HERE TOO:
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "com.lamar.plugin")
    Q_INTERFACES(Plugin_API)

   ...
   // Overide the signal method:
   signals:
    void send_msg(const QString msg) override;

In my Main Application header main.h I have:

public slots:
    void receive_msg(const QString msg);

And finally, the implementaion of the main application slot is:

void main_app::receive_msg(const QString msg)
{
    qDebug() << "I RECEIVE THIS MSG: " << msg;
}

Thank you @SGaist and @jsulm for your help and patience!

[SGaist]

Hi,

Well, you load your plugin and then call the corresponding method from its interface.

What have you tried ?

[fem_dev]

@SGaist Sorry, but I'm not seeing how can I do it. Could you help me?

How the main application will know when the button save was clicked in the plugin UI window?
Is possible to inform that only using interfaces? Or I need to use signals and slots.

Today I tried to connect the plugin and the main app using signals and slots.
So, inside the plugin.cpp in the constructor(), I type:

connect(this, SIGNAL(send_msg(QString)), ???, SLOT(receive_msg(QString)));

But, what I have to write in ????

Obs.: I'm loading the plugins using QPluginLoader:

QPluginLoader loader(file);
loader.load()
Plugin_API* plugin = qobject_cast<Plugin_API*>(loader.instance());

I'm confused about this topic...
Could you please help me a little more?

[jsulm]

@fem_dev Do not connect inside plug-in as it does not know anything about receiver of its signals (and it should not!).
Do the connect in main window (or where-ever you use the plug-in).
So, like

MainWindow::MainWindow(...)
{
    connect(plugin, SIGNAL(send_msg(QString)), this, SLOT(receive_msg(QString)));
}

plugin->data_from_plugin2app();

[fem_dev]

@jsulm thank you....I think that this is the half of solution...

foreach(QString file, plugins) {
        QPluginLoader loader(file);
        if(loader.load())
        {
            Plugin_API* plugin = qobject_cast<Plugin_API*>(loader.instance());

            if(plugin) {
                // HERE I GOT A COMPILATION ERROR:
                // Cannot convert argument 1 from 'Plugin_API *' to 'const QObject *'
                connect(plugin, SIGNAL(send_msg(QString)), this, SLOT(receive_msg(QString)));   
            } else {
                qCritical() << "Wrong Plugin API! Could not cast: " << loader.fileName();
            }
        } else {
            qCritical() << "ERROR: " << loader.fileName() << " - Msg: " << loader.errorString();
        }
    }

Buy my plugin.h have Q_OBJECT macro:

#ifndef PLUGIN_H
#define PLUGIN_H

#include <QObject>
#include <QtPlugin>

#include <QJsonDocument>
#include <QJsonArray>
#include <QJsonObject>
#include <QFile>
#include <QByteArray>

#include "analysis_x_global.h"
#include "../plugin_api.h"
#include "dialog.h"

class PLUGIN_SHARED_EXPORT Plugin: public QObject, public Plugin_API
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "com.lamar.plugin")
    Q_INTERFACES(Plugin_API)

public:
    explicit Plugin(QObject* parent = nullptr);
    ~Plugin() override;

    QJsonObject get_data(void) override;
    void open_ui(const QJsonObject ui_data) override;
    void run(const int job_id) override;

signals:
    void send_msg(const QString msg);

public slots:
    void onMessage(QJsonObject updated_ui_data);
};

#endif // PLUGIN_H

Second: to call a plugin method from the main app, I know that can be done using:

plugin->method()

But my plugin have a Window (UI) and some buttons, like save.
How can I send a plugin data to my main app when the user hits the save button in the plugin Window UI?

[jsulm]

@fem_dev said in Send QJsonObject from plugin to main app:

How can I send a plugin data to my main app when the user hits the save button in the plugin Window UI?

Via signals/slots.

"Cannot convert argument 1 from 'Plugin_API *' to 'const QObject *'" - this is because your plug-in class is not derived from QObject and does not contain Q_OBJECT macro.

[fem_dev]

@jsulm please, look my plugin.h header above. It have the Q_OBJECT macro.
And the class declaration is:

class PLUGIN_SHARED_EXPORT Plugin: public QObject, public Plugin_API

What is wrong?

I tried to add the public QObject and Q_OBJECT macro inside the plugin_API class, but I got these compilation warnings/errors:

'Plugin': base-class 'QObject' is already a base-class of 'Plugin_API'

[jsulm]

@fem_dev said in Send QJsonObject from plugin to main app:

What is wrong?

Problem is that plugin bellow is Plugin_API* and not Plugin*:

connect(plugin, SIGNAL(send_msg(QString)), this, SLOT(receive_msg(QString))); 

Cast to Plugin* instead of Plugin_API*.

[fem_dev]

@jsulm it's not possible because I have many different plugins that share the same Plugin_API...

As you can see in the top, the Plugin_API have all methods that I use in all different plugins.

So, when I load all plugins inside a foreach() loop, I have to cast they using the Plugin_API.

Each individual plugin inherit the Plugin_API class.
And inside each individual plugin I have declared:

class PLUGIN_SHARED_EXPORT Plugin: public QObject, public Plugin_API
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "com.lamar.plugin")
    Q_INTERFACES(Plugin_API)

What I'm doing wrong?

[fem_dev]

Thank you @SGaist and @jsulm
With your help I think that I found a solution! Here is the code:

My plugin interface is called Plugin_API. So the plugin_api.h is:

#ifndef PLUGIN_API_H
#define PLUGIN_API_H

#include <QString>
#include <QDebug>
#include <QJsonObject>
#include <QObject>

// You have to import and inherit QOBject in the plugin interface
class Plugin_API : public QObject
{
    // USE Q_OBJECT MACRO inside the interface
    Q_OBJECT
public:
    virtual ~Plugin_API() = default;

    virtual QJsonObject get_data(void) = 0;
    virtual void set_project_path(const QString project_path) = 0;
    virtual void open_ui(const QJsonObject ui_data) = 0;
    virtual void run(const int job_id) = 0;

    // ===== SIGNALS ===== //
    // You have to declare the signals in the interface too:
    virtual void send_msg(const QString msg) = 0;
};

// Declare our interface:
Q_DECLARE_INTERFACE(Plugin_API, "com.lamar.plugin")

#endif // PLUGIN_API_H

After that, in the plugin.h I have:

// Do NOT inherit plublic QObject here:
class PLUGINSHARED_EXPORT Plugin: public Plugin_API
{
    // ADD Q_OBJECT MACRO HERE TOO:
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "com.lamar.plugin")
    Q_INTERFACES(Plugin_API)

   ...
   // Overide the signal method:
   signals:
    void send_msg(const QString msg) override;

In my Main Application header main.h I have:

public slots:
    void receive_msg(const QString msg);

And finally, the implementaion of the main application slot is:

void main_app::receive_msg(const QString msg)
{
    qDebug() << "I RECEIVE THIS MSG: " << msg;
}

Thank you @SGaist and @jsulm for your help and patience!