Saving the whole application state( ```QTableWidget```, ```QPushButton```, ```QProcess```, objects created with ```new```)

hbatalha

Hello everyone!!

I am new to Qt and I just learned how to use QSettings to save basic things like 'confirm_on_exit' from a checkbox.

And now I want something much more complex.

In the application I have a QTableWidget which stores a lot rows and in each row I have 2 widgets (QPushButton) and some other texts in the columns. Each of these cellwidgets are created dynamically, they are related to the row they are in and there are a bunch of connect's to perform a lot of things in that row.
Also, when each row is created there is an instance of a class that is created for it that contains some stated and in that class there is a function that is immediately called that creates a new QProcess.

It would be unacceptable for the user to close the application and lose all the stuff on the QTableWidget.

I want to save all of that so when the user restarts the application nothing would be lost.

I have no idea on how to this as I have read the entire QSettings documention and found nothing that allows me to do that( I am hoping I missed something).

My actual code is much bigger than this, this is some basic example thta hopefully will illustrate what I want.

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    ui->tableWidget->setColumnCount(4);

    QStringList headers;
    headers << "Header1" << "Header2";

    ui->tableWidget->setHorizontalHeaderLabels(headers);
    ui->tableWidget->setHorizontalHeaderItem(2, new QTableWidgetItem(""));
    ui->tableWidget->setHorizontalHeaderItem(3, new QTableWidgetItem(""));
    ui->tableWidget->setColumnWidth(0, 400);
    ui->tableWidget->setColumnWidth(1, 50);

    ui->tableWidget->setShowGrid(false);
}

void MainWindow::on_pushButton_4_clicked()
{
    QStringList args;

    for(qsizetype i = 0, len = some_number; i < len; ++i)
    {
        args << "some_args"; 

        const int dest_row = ui->tableWidget->rowCount();

        ui->tableWidget->setRowCount(dest_row + 1);

        QPushButton* button1 = new QPushButton();
        pause_button1->setIcon(QIcon(QPixmap(":/Icons/Icons/icon1.png")));

        QPushButton* button2= new QPushButton();
        cancel_button->setIcon(QIcon(QPixmap(":/Icons/Icons/icon2.png")));


        ui->tableWidget->setItem(dest_row, 0, new QTableWidgetItem("Text1");
        ui->tableWidget->setItem(dest_row, 1, new QTableWidgetItem("Text2"));
        ui->tableWidget->setCellWidget(dest_row, 2, button1 );
        ui->tableWidget->setCellWidget(dest_row, 3, button2);

       FooClass *foo_class = new FooClass(args);
 
        connect(button1, SIGNAL(clicked(bool)), this, SLOT(someTask(bool))); 
       
        connect(button2, SIGNAL(clicked()), foo_class , SLOT(sometask()));

         connect(cancel_button, &QPushButton::clicked, [this, button1, button2, args]()
        
                    // some code
        
                    });

        vector_to_hold_FooClass_instances.push_back(foo_class );

        QSring arg = args.join(" ");

        QMap_args_rows[dest_row] = arg;

        foo_class->start();

        args.clear();
    }
}

FooClass

class FooClass: public QObject
{
    Q_OBJECT

public:
    FooClass(QStringList argmnts);

    void start();

    // some states
    bool isPaused();
    bool shouldResume();
    bool isCanceled();

    QString filename;
    QString args;

signals:
     // some signals

public slots:
     // some slots
};


FooClass::FooClass(QStringList argmnts) : args(argmnts)
{
    paused = false;
    resume = false;
    canceled = false;
}

void FooClass::start()
{
    paused = false;
    resume = false;
    canceled = false;

    process = new QProcess;

    connect(process, SIGNAL(readyRead()), SLOT(someTak()));

    process->setProcessChannelMode(QProcess::MergedChannels);

    connect(process, &QProcess::stateChanged, [this](QProcess::ProcessState newState)
    {
        if(newState == QProcess::NotRunning)
        {
            process->deleteLater();
            process = nullptr;

            emit processFinished();
        }
    });

    process->start("program.exe", args);
}

SGaist

Hi,

Yes there is, check beginGroup and beginWriteArray.

You can then neatly store each rows data/state.

You might also want to consider having a dedicated function which creates a "state" of your widget such that it can be reloaded a bit like QMainWindow.

hbatalha

@SGaist said

Yes there is, check beginGroup and beingArray.
…
You can then neatly store each rows data/state.

I have checked them out but didn't understand how I would do that.
Can you provide me with some basic usage code just to give a head start and an idea?

SGaist

My bad it was beginWriteArray.

You have examples in the documentation of both methods.

Did you check them ?

JonB

@hbatalha
While you can try to write code to "creates a "state" of your widget such that it can be reloaded ", from experience you will probably be better if you can express and keep a model of your current state and save/restore that.

If using QTableWidget you should be saving its model(), not the widget itself. And be able to recreate its items from that.

QWidgets are not intended to be saved. In any case, when you say

there are a bunch of connect's to perform a lot of things in that row

If you are doing connect()s dynamically you will not want to try to serialize connections. It is preferable to rebuild these at load time from a model.

hbatalha

@SGaist said

Did you check them ?

Yes, but couldn't see how I would use that on a QTableWidget in my case.

kshegunov

You can't, not out of the box. You can store the window's geometry and such, but storing a (child) widget state makes no sense. Firstly the geometry of the children is controlled by the layouts, so it's not something one usually concerns oneself with. And secondly the data backing the widgets/views may not be available, loaded or even accessible on a second run, so you need to guarantee a consistent state yourself.

hbatalha

@JonB said

If using QTableWidget you should be saving its model(), not the widget itself. And be able to recreate its items from that.
Something like this?

 QSettings qsettings(QSettings::IniFormat, QSettings::UserScope, "Company", "App");

 qsettings.setValue("TableModel", QVariant::fromValue(ui->tableWidget->model()));

kshegunov

No, no. QObjects are not serializable by themselves. You are not going to find a straightforward and simple solution to what you're looking for. You must write your own code, handling your own use case.

JonB

@hbatalha
Unfortunately I think not :( But note that I have not tried this --- have you? I cannot imagine that any Qt model is serializable, so what does QVariant::fromValue(ui->tableWidget->model()) actually produce?

So, unless that works (please tell me if it does!), I meant it is your job to iterate all the rows/columns saving whatever data role values you have stored in it, such that you can reconstruct the model when you deserialize that data. The issue of storing the serialization on a QSettings is a detail. One possibility would be to save the data as JSON in a single setting's key's value.

hbatalha

@JonB said

So, unless that works (please tell me if it does!)

Yes it "works", it does save some values in the ini file, but don't know what they mean nor how I can load from that as I can't convert QVariant to QAbstractItemModel*.

JonB

@hbatalha

Yes it "works", it does save some values in the ini file

I really don't think it does (i.e. save the table contents/info)! And nor does @kshegunov. What exactly does that line produce? If it's a few bytes long, it can't possibly be the necessary information to reconstruct :)

hbatalha

@kshegunov said

You can't, not out of the box

So any idea on how I can achieve that?

JonB

@hbatalha
The way I said! You have to save what you want from the model with your own code. There isn't a magic wand. Both of us are telling you that! But doing it this way is likely to be a lot easier than actually trying to serialize a model or a widget with all its properties/attributes etc. as an object.

hbatalha

@JonB
I don't think it does neither. That's why I had 'works' in quotes. What I meant is that it compiles and save some stuff in the file. And then I saw that the application informs that it can't save QAbstractItemModel*

This is what it saves to the file App.ini:

[General]
TableModel=@Variant(\0\0\0\x7f\0\0\0\x14QAbstractItemModel*\0)

JonB

@hbatalha
Yes, that is what I/ @kshegunov expected. All it's serializing is the pointer value with its type name! Because that's all it knows how to do. And will never get further, you have to write the code to serialize/save the data in the model, and to restore it. Which I think is easier than trying to serialize/save the widgets/the visible table for restoration.

hbatalha

@JonB said

The way I said! You have to save what you want from the model with your own code. There isn't a magic wand. Both of us are telling you that! But doing it this way is likely to be a lot easier than actually trying to serialize a model or a widget with all its properties/attributes etc. as an object.

yeah, I already thought about a way to do that, it requires me to change a lot of working code but that seems to be the way to do it. I will get back to you once I finish.

hbatalha

@JonB, @SGaist , @kshegunov

I am happy to inform that I have achieved the goal stated in the OP.

What I did was create a function that that stores all the instances info in the QSettings and another function that will will create all the rows in the QTableWIdget from the info saved.

Something like this:


void saveSetting()
{
    QSettings qsettings(QSettings::IniFormat, QSettings::UserScope, "Company", "APP");

    qsettings.beginWriteArray("Table");
    qsettings.remove("");
    qsettings.endArray();

    qsettings.beginWriteArray("Table");
    for(qsizetype i = 0, len = vector_to_hold_FooClass_instances.size(); i < len; ++i)
    {
        qsettings.setArrayIndex(i);
        qsettings.setValue("args", vector_to_hold_FooClass_instances.at(i)->getArgs());

         // I replaced the statuses with enum class instead of using ``bool``
         // I couldn't find a better t save enum class to QSettings so I used this workaround
        qsettings.setValue("status", static_cast<int>(vector_to_hold_FooClass_instances.at(i)->status));
    }
    qsettings.endArray();

}

and on loading:

void MainWindow::loadSettings()
{
    QSettings qsettings(QSettings::IniFormat, QSettings::UserScope, "HBatalha", "Table");

   int size = qsettings.beginReadArray("Table");
   
   for(int i = 0; i < size; ++i)    
   {        
        QStringList args = qsettings.value("args").toString().split(" ");
        
        FooClass::Status status = static_cast<FooClass::Status>(qsettings.value("status").toInt());        
       const int dest_row = ui->tableWidget->rowCount();

        ui->tableWidget->setRowCount(dest_row + 1);

        QPushButton* button1 = new QPushButton();
        pause_button1->setIcon(QIcon(QPixmap(":/Icons/Icons/icon1.png")));

        QPushButton* button2= new QPushButton();
        cancel_button->setIcon(QIcon(QPixmap(":/Icons/Icons/icon2.png")));


        ui->tableWidget->setItem(dest_row, 0, new QTableWidgetItem("Text1");
        ui->tableWidget->setItem(dest_row, 1, new QTableWidgetItem("Text2"));
        ui->tableWidget->setCellWidget(dest_row, 2, button1 );
        ui->tableWidget->setCellWidget(dest_row, 3, button2);

       FooClass *foo_class = new FooClass(args);
        foo_class->status = status;
 
        connect(button1, SIGNAL(clicked(bool)), this, SLOT(someTask(bool))); 
       
        connect(button2, SIGNAL(clicked()), foo_class , SLOT(sometask()));

         connect(cancel_button, &QPushButton::clicked, [this, button1, button2, args]()
        
                    // some code
        
                    });

        vector_to_hold_FooClass_instances.push_back(foo_class );

        QSring arg = args.join(" ");

        QMap_args_rows[dest_row] = arg;

        foo_class->start();

        args.clear();
    }
    qsettings.endArray();
}

What do you guys think?