How to create delegate for QTreeWidget?

Question

Here is what I'm trying to do (all parents and children must have a close button on the right, in the future, only the hovered item will be able to show the **close ** button):

My delegate code:

class CloseButton : public QItemDelegate
{
     Q_OBJECT

public:
     CloseButton( QObject* parent = 0 )
          : QItemDelegate( parent )
     {};

     QWidget* createEditor( QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index ) const
     {
          if ( index.column() == 1 )
          {
               QToolButton* button = new QToolButton( parent );
               button->setIcon( QIcon( CLOSE_ICON ) );
               //button->setFixedSize( 16, 16 );
               //button->setAutoRaise( true );
               //button->setVisible( true );

               CONNECT( button, SIGNAL( clicked() ), this, SLOT( emitCommitData() ) );

               return button;
          }
          return ( new QWidget );
     }

private slots:
     void emitCommitData()
     {
          emit commitData( qobject_cast< QWidget* >( sender() ) );
     }

private:
     //Q_DISABLE_COPY( CloseButton );
};

With QTreeWidget connection code:

recipientsView()->setItemDelegateForColumn( 1, new CloseButton( this ) );

where recipientsView() is a simple QTreeWidget.

Problem is that QToolButtons are not shown at all (it must be in the second column, i.e. column index in the tree is 1). What I'm doing wrong?

I have checked already all Qt demo examples about delegates and the first Google result about QItemDelegate's and similar stuff.

Answer 1

You can use the QStyledDelegate::paint function to draw the close icon, without using any widget, and the editorEvent to receive mouse events for the item, even if you don't use the editor or make the item editable.

class CloseButton : public QStyledItemDelegate {
    Q_OBJECT
public:

    explicit CloseButton(QObject *parent = 0, 
                         const QPixmap &closeIcon = QPixmap())
        : QStyledItemDelegate(parent)
        , m_closeIcon(closeIcon)
    {
        if(m_closeIcon.isNull())
        {
            m_closeIcon = qApp->style()
                ->standardPixmap(QStyle::SP_DialogCloseButton);
        }
    }

    QPoint closeIconPos(const QStyleOptionViewItem &option) const {
        return QPoint(option.rect.right() - m_closeIcon.width() - margin,
                      option.rect.center().y() - m_closeIcon.height()/2);
    }

    void paint(QPainter *painter, const QStyleOptionViewItem &option,
               const QModelIndex &index) const {
        QStyledItemDelegate::paint(painter, option, index);
        // Only display the close icon for top level items...
        if(!index.parent().isValid()
                // ...and when the mouse is hovering the item
                // (mouseTracking must be enabled on the view)
                && (option.state & QStyle::State_MouseOver))
        {
            painter->drawPixmap(closeIconPos(option), m_closeIcon);
        }
    }

    QSize sizeHint(const QStyleOptionViewItem &option,
                   const QModelIndex &index) const
    {
        QSize size = QStyledItemDelegate::sizeHint(option, index);

        // Make some room for the close icon
        if(!index.parent().isValid()) {
            size.rwidth() += m_closeIcon.width() + margin * 2;
            size.setHeight(qMax(size.height(),
                                m_closeIcon.height() + margin * 2));
        }
        return size;
    }

    bool editorEvent(QEvent *event, QAbstractItemModel *model,
                     const QStyleOptionViewItem &option,
                     const QModelIndex &index)
    {
        // Emit a signal when the icon is clicked
        if(!index.parent().isValid() &&
                event->type() == QEvent::MouseButtonRelease) {
            QMouseEvent *mouseEvent = static_cast<QMouseEvent*>(event);

            QRect closeButtonRect = m_closeIcon.rect()
                    .translated(closeIconPos(option));

            if(closeButtonRect.contains(mouseEvent->pos()))
            {
                emit closeIndexClicked(index);
            }
        }
        return false;
    }

signals:
    void closeIndexClicked(const QModelIndex &);
private:
    QPixmap m_closeIcon;
    static const int margin = 2; // pixels to keep arount the icon

    Q_DISABLE_COPY(CloseButton)
};

Answer 2

First, I should ask if you are really using a QTreeWidget, or rather a QTreeView? You cannot use custom delegates with a QTreeWidget according to the documentation for QTreeView, and will have to use a QTree*View* and some form of QAbstractItemModel for you to be able to use a custom delegate.

Ah, scratch that. I see that you're calling setItemDelegateForColumn, which is a QTreeView function, but you should be aware of the difference, so I'm keeping the above paragraph. :)

I would check that your model's flags() function is returning Qt::ItemIsEditable as part of its item flags. The createEditor() method is called whenever an edit event is reported by the view. (The view events that will trigger an edit depend on the model's EditTriggers) Usually a double-click on the delegate will trigger an edit by default, among other things.

I doubt that you want the close button to appear only on double-click, though. To get the button to appear all the time, you'll have to reimplement the delegate's paint() function to draw a button, Among other things. I found Qt's StarDelegate example to be quite helpful in this regard, and I suspect you'll find it useful too.