Set Delegate for each cell in a QTableWidget?

[JonB]

@hbatalha
In the example at https://doc.qt.io/qt-5/qabstractitemdelegate.html#details, you see

void WidgetDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
                           const QModelIndex &index) const
{
    if (index.column() == 1) {
        ...
    } else
        QStyledItemDelegate::paint(painter, option, index);
}

WidgetDelegate has been assigned as the item delegate (probably through setItemDelegate()) for all cells. The first thing it does in paint() is to look at the column/row of the passed-in index to see which cell it is being called on, and acts accordingly. This is how you apply a delegate to certain cells only: you have to assign the delegate to all cells and then have it check at runtime what it does/does not do for each cell.

[hbatalha]

@JonB I think the problem is I have two different buttons that goes in their own columns in the same row. I will have to modify the delegate and create two buttons instead that goes in only one column I guess. This shall be the starting point.

[JonB]

@hbatalha
What? Why?

As said before when using the delegate you get an index parameter which you can inspect and act on accordingly for desired rows, columns and/or cells. I don't know what your issue is.

[hbatalha]

@JonB Maybe I am not understanding how to do by your proposed solution, this is the code without delegate:

for(int i = 0, len = titlesList.size(); i < len; ++i) // len == 200 starts causing some lumpiness (at leat leat in my pc)
{
    const int row = ui->table->rowCount();

    ui->table->setRowCount(row + 1);

    QPushButton* button1= new QPushButton(this);
    QPushButton* button2= new QPushButton(this);

    ui->table->setItem(row, 0, new QTableWidgetItem(title));
    ui->table->setItem(row, 1, new QTableWidgetItem("-"));
    ui->table->setItem(row, 2, new QTableWidgetItem("-"));
    ui->table->setItem(row, 3, new QTableWidgetItem("-"));
    ui->table->setItem(row, 4, new QTableWidgetItem("-"));
    ui->table->setCellWidget(row, 5, button1);
    ui->table->setCellWidget(row, 6, button2);


    for(int k = 0; k < 5; ++k)
    {
        QTableWidgetItem* item = ui->table->item(row, k);
        item->setFlags(item->flags() & ~ Qt::ItemIsEditable);

        if(k != 0)
        {
            item->setTextAlignment(Qt::AlignmentFlag::AlignCenter);
        }
    }

    Record* record = new Record(title, destinationFolder, format,
                                  qualityText, mRecordType);
    record->button1(button1);
    record->button2(button2);

    allRecords.append(record);
    activeRecords.append(record);
    database.add(record);
}

Each button click causes an action to its row. How would I do that with the delegate class above?

[VRonin]

@hbatalha said in Set Delegate for each cell in a QTableWidget?:

How would I do that with the delegate class above?

DelegateButton *delegate1 = new DelegateButton(this);
DelegateButton *delegate2 = new DelegateButton(this);
view->setItemDelegateForColumn(5,delegate1);
view->setItemDelegateForColumn(6,delegate2);

[hbatalha]

@VRonin That is how I did, but the problem was that, say that I want to insert 30 rows, only the last delegate2 will be valid for the tablewidget, when I click one button it is supposed to change its icon, so with delegate button, when I click a button in a row, all the others delegate buttons in the other rows will be affected because ultimately they are the same and only last row will be affected. Every time a new row is inserted the new delegate button created will replace the last one with setItemDelegateForColumn.
That is how it behaved.

[Christian Ehrlicher]

Again: change your delegate to check for the index and do the painting accordingly...

[VRonin]

@hbatalha said in Set Delegate for each cell in a QTableWidget?:

when I click one button it is supposed to change its icon, so with delegate button, when I click a button in a row, all the others delegate buttons in the other rows will be affected because ultimately they are the same and only last row will be affected. Every time a new row is inserted the new delegate button created will replace the last one with setItemDelegateForColumn.

What I read in this is that you are storing data in the delegate. that should not happen.
The process should be:
click the delegate➡the delegate emits a signal (clicked(const QModelIndex &index))➡in the slot connected to that signal you store data in a custom role of the model (e.g. model->setData(index, index.data(Qt::UserRole).toBool() ? QVariant() : true, Qt::UserRole);)➡the delegate will use the data stored in this role to decide how to paint/create the button

[hbatalha]

@VRonin @Christian-Ehrlicher There's a disconnect here, I am not quite understanding what you are telling me. This is how my table is behaving:

The last row is being changed because that is the last delegate button that was created. Each record takes the two buttons and they are connected and in turn each record is connected to a table row. So when I click a button it changes the status of the record it's connected to and then the row which the record is connected to is updated.

I need each row to have its own buttons. That's why I said that I need to modify the delegate so it paints two buttons instead like here and then use setItemDelegateForRow.

[VRonin]

The shape of the play/pause button should depend on the data in the model. Coan you show us the slot where you you change the "In Queue" to "Paused"?

[hbatalha]

@VRonin Here are the connect's with QPushButton:

connect(pause_button, &QPushButton::clicked, record, &Record::pauseResume); // `pause_button` is `button1` in the code above
connect(record, &Record::progressUpdated, this, &MainWindow::onProgressUpdated);

The slot:

void MainWindow::onProgressUpdated(const QString& command, QString status)
{
    const int row = commands_rows.key(command); // QMap

    QTableWidgetItem* item = ui->table->item(row, 2);

    bool isPercentage = false;

    int progressPercentInt = status.toInt(&isPercentage);

    if (progressPercentInt < 0)
    {
        status = tr("Error");
        isPercentage = false;
    }

    if(isPercentage)
    {
        item->setText(status + "%");
    }
    else
    {
        item->setText(status);
    }
}

[VRonin]

@hbatalha said in Set Delegate for each cell in a QTableWidget?:

&Record::pauseResume

Can you show this slot please?

[hbatalha]

@VRonin

void Recod::pauseResume()
{ 
    if(isInQueue() || isToResume())
    {
        emit pogressUpdated(command, tr("Paused"));

        if(hasStarted)
        {
            process->kill();
        }

        status_ = Status::PAUSED;
        hasStarted = false;
    }
    else
    {
        emit progressUpdated(command, tr("In Queue"));
        status_ = Status::TO_RESUME;
        emit statusChanged(getArgsStr(), status());
    }
}

[VRonin]

@hbatalha said in Set Delegate for each cell in a QTableWidget?:

status_ = Status::PAUSED;

Yeah, see, you are using a global state to manage data that should live in the model. pauseResume should look more like:

enum{
StatusRole = Qt::UserRole
};
void Recod::pauseResume(const QModelIndex& index){
if (index.data(StatusRole).toInt() == Status::PAUSED)
model->setData(index,Status::TO_RESUME,StatusRole);
else
model->setData(index,Status::PAUSED,StatusRole);
}

This stores the state of the single item into the model. Signaling the change is handled by the model. You can then retrieve that state inside the delegate and paint accordingly

[hbatalha]

@VRonin How I get this part, but since I will be having multiple rows how will I differentiate each delegate button with its row? In my for loop when I insert rows if I call setItemDelegateForColumn only once still all the rows that are inserted after will have the delegate buttons. Shouldn't I be using setItemDelegateForRow instead? Each record takes its buttons but only the last delegate buttons created in the for loop will be set into the columns. This is the part I am not getting.

Sorry it's taking so much time but it's proving to be trickier for me to understand delegates fully. This is my first hands-on experience with them.

[VRonin]

@hbatalha said in Set Delegate for each cell in a QTableWidget?:

Each record takes its buttons but only the last delegate buttons created in the for loop will be set into the columns.

Not sure I understand what you mean.

If showing/not showing the buttons depend on a state of the item then we are back to the case above. Save such state in a role of the model and use it in the delegate.

Maybe if you can formulate a simple concrete example we can get to the root of the problem

[hbatalha]

@VRonin said in Set Delegate for each cell in a QTableWidget?:

Not sure I understand what you mean.

Ok, try having a QTableWidget with multiple rows and use setItemDelegateForColumn to add the delegate buttons like in my code above, then click a button in a row and have only that delegate button in that row be repainted (change icon). This is what I am unable to do.

If you see the image below I click one button and all the other buttons change icon as well. I want to click one button and only that button to change its icon.

Maybe if you can formulate a simple concrete example we can get to the root of the problem

I will try to create one.

[VRonin]

Simplified example:

buttondelegate.h

#ifndef BUTTONDELEGATE_H
#define BUTTONDELEGATE_H

#include <QApplication>
#include <QStyledItemDelegate>
#include <QPushButton>
#include <QPainter>

class ButtonDelegate : public QStyledItemDelegate
{
    Q_OBJECT
#if QT_VERSION >= QT_VERSION_CHECK(5, 13, 0)
    Q_DISABLE_COPY_MOVE(ButtonDelegate)
#else
    Q_DISABLE_COPY(ButtonDelegate)
#endif
public:
    explicit ButtonDelegate(QObject* parent)
        :QStyledItemDelegate(parent)
    {

    }
    void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const Q_DECL_OVERRIDE
    {
        Q_ASSERT(index.isValid());
        QStyleOptionViewItem opt = option;
        initStyleOption(&opt, index);
        const QWidget *widget = option.widget;
        QStyle *style = widget ? widget->style() : QApplication::style();
        QStyleOptionButton buttonOption = buttonOptions(opt,index);
        style->drawControl(QStyle::CE_PushButton, &buttonOption, painter, widget);
    }
    QSize sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const Q_DECL_OVERRIDE
    {
        QStyleOptionViewItem opt = option;
        initStyleOption(&opt, index);
        return buttonRect(opt).size();
    }
    QWidget* createEditor(QWidget *parent, const QStyleOptionViewItem &, const QModelIndex &) const Q_DECL_OVERRIDE
    {
        return new QWidget(parent);
    }
    void setEditorData(QWidget *, const QModelIndex &) const Q_DECL_OVERRIDE
    {

    }
    void setModelData(QWidget *, QAbstractItemModel *, const QModelIndex &) const Q_DECL_OVERRIDE
    {

    }
    void updateEditorGeometry(QWidget *editor, const QStyleOptionViewItem &option, const QModelIndex &index) const Q_DECL_OVERRIDE
    {
        QStyleOptionViewItem opt = option;
        initStyleOption(&opt, index);
        editor->setGeometry(opt.rect);
        const QRect butRect = buttonRect(opt);
        QWidget* baseEditor = editor->findChild<QWidget*>("baseEditor");
        Q_ASSERT(baseEditor);
        baseEditor->setGeometry(0,0,opt.rect.width()-butRect.width(),opt.rect.height());
        QWidget* myButton = editor->findChild<QWidget*>("myButton");
        Q_ASSERT(myButton);
        myButton->setGeometry(opt.rect.width()-butRect.width(), 0, butRect.width(),butRect.height());
    }
Q_SIGNALS:
    void clicked(const QModelIndex &index);
protected:
    bool editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index) override
    {
        Q_ASSERT(event);
        Q_ASSERT(model);
        Qt::ItemFlags flags = model->flags(index);
        if ((option.state & QStyle::State_Enabled) && (flags & Qt::ItemIsEnabled))
        {
            switch (event->type()){
            case QEvent::MouseButtonRelease:{
                QStyleOptionViewItem viewOpt(option);
                initStyleOption(&viewOpt, index);
                QMouseEvent *me = static_cast<QMouseEvent*>(event);
                if (me->button() == Qt::LeftButton)
                {
                    currentIndex = index;
                    clickedHelper();
                }
            }
                break;
            default:
                break;
            }
        }
        return QStyledItemDelegate::editorEvent(event,model,option,index);
    }
    virtual QStyleOptionButton buttonOptions(const QStyleOptionViewItem &option, const QModelIndex &index, bool skipRct=false) const
    {
        QStyleOptionButton buttonOption;
        buttonOption.icon = m_buttonIcon;
        if(index.data(Qt::UserRole).toBool())
            buttonOption.text = QString(QChar(0x23F8)); //pause button emoji
        else
            buttonOption.text = QString(QChar(0x25B6)); //play button emoji
        buttonOption.rect = skipRct ? QRect() : buttonRect(option);
        buttonOption.features = QStyleOptionButton::None;
        buttonOption.direction = option.direction;
        buttonOption.fontMetrics = option.fontMetrics;
        buttonOption.palette = option.palette;
        buttonOption.styleObject = option.styleObject;
        return buttonOption;
    }
    virtual QRect buttonRect(const QStyleOptionViewItem &option) const
    {
        return option.rect;
    }

private:
    mutable QModelIndex currentIndex;
    QString m_buttonText;
    QIcon m_buttonIcon;
    void clickedHelper()
    {
        clicked(currentIndex);
    }

};
#endif // BUTTONDELEGATE_H

main.cpp

#include <QApplication>
#include <QTableWidget>
#include "buttondelegate.h"

int main(int argc, char *argv[])
{
    QApplication app(argc,argv);
    QTableWidget wid(10,2);
    for(int i=0;i<10;++i){
        wid.setItem(i,0,new QTableWidgetItem(QStringLiteral("Item %1").arg(i+1)));
    }
    ButtonDelegate* buttonDelegate = new ButtonDelegate(&wid);
    QObject::connect(buttonDelegate,&ButtonDelegate::clicked,&wid,[&wid](const QModelIndex& index){
        Q_ASSERT(index.model()==wid.model());
        wid.model()->setData(index,index.data(Qt::UserRole).toBool() ? QVariant() : true,Qt::UserRole);
    });
    wid.setItemDelegateForColumn(1, buttonDelegate);
    wid.show();
    return app.exec();
}

[hbatalha]

@VRonin This one seems to be the solution I have been looking for. I will, however, have to hack my current code to using this solution. In case of any question I will reach out to you.

Thank you for taking so much time and having so much patience with me. I appreciate it.

[hbatalha]

@VRonin hi, I have finished modifying the delegate button so I can use it in my code and it works fine.
However, I am wondering how can I set a stylesheet for it. With my old QPushButton I had it like this:

QPushButton* cancel_button = new QPushButton(this);
cancel_button->setIcon(QIcon(QPixmap(":/Icons/cancel.png")));
cancel_button->setStyleSheet("QPushButton{background-color: transparent; background-repeat: none; border: none;}  QPushButton:pressed{ background-color: transparent; }");

Can I do it with the delegate button? The reason I want to do this is because I want the the button to display only the icon I set for it.

Edit: I think I have solved it by going in the QStyleOptionButton buttonOptions(const QStyleOptionViewItem &option, bool skipRct=false) const function and change the QStyleOptionButton features to flat:

        QStyleOptionButton buttonOption;
        buttonOption.features = QStyleOptionButton::Flat;