Insert fill circle into cell of QTableWidget

  • Lifetime Qt Champion

    The timer is meant as a way of not strangulating the event loop.
    its not as fast a tight loop as it goes over the event loop but it
    allows redraw of the view. ( which also uses the event loop to actually redraw)
    Anyway, you are looping row x colSize ( actually rox x row ??)
    and then allow event loop.
    maybe you mean like this ?

     while (count < 1500) {
            for(int i = 0; i < rowSize(); i++) {
                for(int j = 0; j < rowSize(); j++) { // should this not be colSize ?

  • @mrjj said in Insert fill circle into cell of QTableWidget:


    Row x Row is because the rows will really be the same as the columns.

    I have also tried to locate QCoreApplication :: processEvents (); in that position, with the same effect, that is, it does not update well in the UI.

    If the timer does not penalize the execution time of the program and only acts in the reprssentación of the UI, it could be good. How should I do it?

  • Lifetime Qt Champion


    • it does not update well in the UI.

    meaning it does update sometimes or what result do you get ?

    here is sample of changing random cell

    int random(int min, int max) //range : [min, max)
        static bool first = true;
        if (first) {
            srand( time(nullptr) ); //seeding for the first time only!
            first = false;
        return min + rand() % (( max + 1 ) - min);
    void MainWindow::changeVal()
        auto timer = new QTimer(this);
        QObject::connect(timer, &QTimer::timeout, [this]() {
            int rowCount = this->model->rowCount(QModelIndex());
            int colCount = this->model->columnCount(QModelIndex());
            this->model->setData(model->index(random(0, rowCount), random(0, colCount)), random(0, 20), Qt::EditRole);
    Note that sample will create a timer each time you select Change val menu so
    its better to move timer as member. 
    Also it uses a lambda as slot. you can use a normal slot for it and let it be part of World class.
    • If the timer does not penalize the execution time of the program
      it does to some degree. But even using Threads, you will have to ask it to update and redraw
      over the event loop as the VIEW cannot update if you strangulate it using tight loops.

    But using timer is not super slow.
    alt text
    (video is actually slower than real deal)

  • @mrjj

    meaning it does update sometimes or what result do you get ?

    Means that the UI is only updated if I interact with it, that is, if for example I select the cells, then it shows the changes made in the code.

    But using timer is not super slow

    Yes but in the parallel version it should go faster and if I use a timer, it will always take the same time, because the time depends on the timer variable.

    Video with an example of what happens to me:


    Change button calls the InitializeWorld() method.

  • Lifetime Qt Champion

    @juaniyoalm said in Insert fill circle into cell of QTableWidget:

    • it will always take the same time, because the time depends on the timer variable.

    Not really. the timer will call your function at a fix time. Your function will take the time it takes but using a timer, its all driven like a loop but allows the event to run to the view can update.

    Anyway, what you are seeing is expected.
    You are modifying the vector list BEHIND models back. It dont know you changed some of its data so first when you click something, view re-reads the cells and draws the values.

    Recall the setData.

    bool CellModel::setData(const QModelIndex &index, const QVariant &value, int role)
        auto RowCount = this->mundo->world.size();
        auto ColCount = this->mundo->world[0].size();
        qDebug () << "role=" << role;
        if (index.isValid()            
                && role == Qt::EditRole
                && index.row() < RowCount
                && index.row() >= 0
                && index.column() <  ColCount
                && index.column() >= 0
           ) {
            int row = index.row();
            int col = index.column();
            emit dataChanged(index, index);
            return true;
        return false;

    here we emit dataChanged so view knows something changed.
    when you do
    you are not telling model/view you changed the list and that is why
    QCoreApplication::processEvents(); do not help.

  • But if you modified only the value of a cell if work fine.

    How could I then modify the value? It has to be modified from the world class. Could I put a signal when modified with the setdata method?

  • Lifetime Qt Champion

    You can add add signal to World class and connect it to the model. and then emit it
    to have model call DataChanged. OR give World a pointer to the model and use models
    API to change data and inform view.

    • But if you modified only the value of a cell if work fine.
      im not sure what u say here.

  • @mrjj
    I want to say that if I do this


    The UI update fine and model unknown data either

  • Lifetime Qt Champion

    Ok. not really sure how,
    but didnt check the latest version.
    Also if the VIEW get an update/paintEvent it will re-read the indexes so i guess
    its via the normal paint/update/redraw.

  • @mrjj

    I have already solved the problem. I have created a signal in the Cell class that is emited when the value of the cell is modified. This signal sends the cell to the slots. Then I created a slot in the MainView class and connected each cell of the model's matrix with that slot. This slot creates a QModelIndex and issues a dataChanged for the model to update the view. Besides, I had to save the position of the cell in the cell class.

    Emit Signal:

    void Cell::setFood(int food)
        if(this->fungus != food) {
            this->fungus = food;
            emit this->updateModel(this);


    void MainWindow::foodChanged(Cell *cell)
        QModelIndex aux = model->index(cell->place.first, cell->place.second);
        model->dataChanged(aux, aux);


        for (int i = 0; i < this->rows; i++) {
            for (int j = 0; j < this->columns; j++) {
                connect(this->model->mundo->getCell(i, j), &Cell::updateModel, this, &MainWindow::foodChanged);

    Now I need pass the value of the circle also in the data method so that the delegate's paint method can receive it ...
    Any example of how to do it?

  • Lifetime Qt Champion

    As I already suggested many times: use custom roles. So in your paint function, request the data using the roles specific to the parameters you want to get.

  • @SGaist

    Yes, but I unknown how to do it...

  • Lifetime Qt Champion

    QVariant data = model->data(MyModel::MyCustomRole);

    In your model:

    QVariant MyModelModel::data(const QModelIndex &index, int role = Qt::DisplayRole) const
    // usual stuff
    if (role == MyModel::MyCustomRole) {
        return mound->getCell(index.row(), index.column())->myCoolProperty;

  • @SGaist

    But I need both values to be at the same time in the delegate's paint method.

    I modify the value of the items of the cells in internal methods of the World class, not from model, then emit signal that is received by the slot located in the MainWindows class and this emit dataChange signal of the model, as I wrote before.

  • Lifetime Qt Champion

    Can we talk about the actual data ?
    What is the data for the circle ?
    you say "value of the circle"
    can u specify what that means ?
    The delegate has access to the cell so it can have any values at the same time.
    So to avoid confusing, could you tell what data you need to paint the circle ?

  • @mrjj
    Yeah, I need size array of fungivores in each cell to paint circle. This value can get it whit a method of Cell class.

    The data method of model can you see above.

  • Lifetime Qt Champion

    well just do as @SGaist suggests and the delegate can use your custom role(s)
    to get the data it needs.
    user roles are nothing complicated at all.
    its just an id that let you assign a vlue to that id for an index.
    model->setData(model->index(0,0), 90 , Qt::UserRole + 1 );

    To avoid to ugly code and stupid mistakes, we define it as a const.
    constexpr int CircleData = Qt::UserRole+1;
    constexpr int SomeOtherData = Qt::UserRole+2;

    and use instead of the raw value. This is a must to do. :)

  • @mrjj
    But the problem is that I don't change the value with model->setData...., as I told you, I change it with methods place in Cell class and after emit signals to notified to model and call dataChanged method...

  • Lifetime Qt Champion


    i dont see that matters with roles.
    the delegate ask model and model get from the vector/cell so
    should just be fine.

  • @mrjj

    I can not return a cell in the data method of the model because it gives me an error:


  • Lifetime Qt Champion

    you try to return a Cell pointer.
    Should be like
    mundo->getCell(index.row(), index.column())->somePublicVariable
    mundo->getCell(index.row(), index.column())->Func(); // return some data, int , float , etc

    Why you want to return the cell pointer ?
    Just return some of its data

  • @mrjj

    I think I'm not understanding ... hah.

    If I put the following:


    When I modify the value in this method:


    Or these:


    That signals activate this method (slot):


    But in no time I pass the role and then the model does not know what data to return...

  • Lifetime Qt Champion

    The view itself ask for
    Qt::DisplayRole and Qt::EditRole ( if u edit cell )
    the new roles was for the delegate to request data it needs.

    You did study for more than a few minutes the
    right ?

  • @mrjj

    Ok, I understand now. The problems are solved:

    QVariant CellModel::data(const QModelIndex &index, int role) const
            return QVariant();
        if(index.row() >= mundo->getWorld().size() || index.row() < 0 ||
               index.column() >= mundo->getWorld()[0].size() || index.column() < 0)
            return QVariant();
        if(role == CircleSize)
            return this->mundo->getCell(index.row(), index.column())->getFungivoresSize();
        if(role == FoodCount)
            return this->mundo->getCell(index.row(), index.column())->getFood();
        return QVariant();

    And paint method:

    void CellDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
        int cellValue = index.model()->data(index, Qt::UserRole+2).toInt();
        qreal circleValue = index.model()->data(index, Qt::UserRole+1).toInt();
        qreal circleRealValue = (circleValue*20)/50;
        painter->fillRect(option.rect, QBrush(QColor((255 - cellValue), 255, 51)));
        painter->drawEllipse(static_cast<QPointF>(, circleRealValue, circleRealValue);
        painter->setRenderHint(QPainter::Antialiasing, true);

  • Lifetime Qt Champion

    Note you should try to reuse the CircleSize, FoodCount constexpr if possible
    instead of Qt::UserRole+1.
    you can just make a .h file and put them there and let both
    model and delegate include it.

  • @mrjj

    Ok I have already done it.

    I want to thank all of you who have tried to help me, especially @mrjj and @SGaist . You have had a lot of patience with me. Thank you.

    Surely I will have more questions about the project later. I'll stay here.

  • Lifetime Qt Champion

    Well good work then. :)
    Please mark as solved.
    You can always make new posts
    for new problems.

    and happy programming.

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