Using QAbstractItemDelegate to display a TGA from a database

[victor.fernandez]

You may paint to cell blank when you don't have the data, then store the index in an array and use a timer with setSingleShot(true) and the interval you want. Connect the timeout() signal to a slot where you call view->update(index) for all the indexes that need to be repainted.

class SQLQueryItemDelegate : public QStyledItemDelegate
{
...
signals:
    void paintingDeferred(const QModelIndex& index);
...
};
 
class SQLQueryDeferredPainter : public QObject
{
    Q_OBJECT
 
public:
    SQLQueryDeferredPainter(QAbstractItemView *view, SQLQueryItemDelegate *delegate, QObject *parent);
 
protected slots:
    void paintLater(const QModelIndex& index);
    void paintPendingIndexes();
 
protected:
    QModelIndexList m_indexes;
    QAbstractItemView *m_view;
    QTimer m_timer;
};
 
SQLQueryDeferredPainter::SQLQueryDeferredPainter(QAbstractItemView *view, SQLQueryItemDelegate *delegate, QObject *parent)
 : QObject(parent)
{
    m_view = view;
 
    connect(delegate, SIGNAL(paintingDeferred(const QModelIndex&)),
            this, SLOT(paintLater(const QModelIndex&)));
 
    m_timer.setSingleShot(true);
    m_timer.setInterval(100);
    connect(&m_timer, SIGNAL(timeout()),
            this, SLOT(paintPendingIndexes()));
}
 
void SQLQueryDeferredPainter::paintLater(const QModelIndex& index)
{
    m_indexes.append(index);
    m_timer.start();
}
 
void SQLQueryDeferredPainter::paintPendingIndexes()
{
    foreach(const QModelIndex& index, m_indexes)
        m_view->update(index);
 
    m_indexes.clear();
}

class SQLQueryItemDelegate : public QStyledItemDelegate
{
...
signals:
    void paintingDeferred(const QModelIndex& index);
...
};

class SQLQueryDeferredPainter : public QObject
{
    Q_OBJECT

public:
    SQLQueryDeferredPainter(QAbstractItemView *view, SQLQueryItemDelegate *delegate, QObject *parent);

protected slots:
    void paintLater(const QModelIndex& index);
    void paintPendingIndexes();

protected:
    QModelIndexList m_indexes;
    QAbstractItemView *m_view;
    QTimer m_timer;
};

SQLQueryDeferredPainter::SQLQueryDeferredPainter(QAbstractItemView *view, SQLQueryItemDelegate *delegate, QObject *parent)
 : QObject(parent)
{
    m_view = view;

    connect(delegate, SIGNAL(paintingDeferred(const QModelIndex&)),
            this, SLOT(paintLater(const QModelIndex&)));

    m_timer.setSingleShot(true);
    m_timer.setInterval(100);
    connect(&m_timer, SIGNAL(timeout()),
            this, SLOT(paintPendingIndexes()));
}

void SQLQueryDeferredPainter::paintLater(const QModelIndex& index)
{
    m_indexes.append(index);
    m_timer.start();
}

void SQLQueryDeferredPainter::paintPendingIndexes()
{
    foreach(const QModelIndex& index, m_indexes)
        m_view->update(index);

    m_indexes.clear();
}

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