bool somethingChanged( QProgressDialog & progress );

// вызов
if (!somethingChanged(progress)) return false;

#define UPDATE_STEP	100

bool UpdateProgress( QProgressDialog & progress, int row )
{
	if ((row + 1) % UPDATE_STEP) return true;		// update once per UPDATE_STEP
	progress.setValue(row);					// calls processEvents for modal dialog
	return progress.wasCanceled();
}

bool Spreadsheet::sort_data( const QList<QTableWidgetSelectionRange> & range, const SpreadsheetCompare & compare )
{
	if(range.isEmpty()) return false;

	QProgressDialog progress(this);
	progess.setModal(true);				// should be modal
	
// check range
	progress.setLabelText(tr("Checking range"));
	progress.setMaximum(range.size());
	for (int it = 0; it < range.size(); it++) {
		if (range[it].leftColumn() < 0) return false;
		if (range[it].bottomRow() < 0) return false;
		if (range[it].rightColumn() < 0) return false;
		if (range[it].topRow() < 0) return false;
		if (!UpdateProgress(progress, it)) return false;
	}

// fill columns 
	QList<int> columns;
	QList<int> rows_n;
	
	progress.setLabelText(tr("Adding rows & columns"));
	progress.setMaximum(range.size());
	progress.setValue(0);
	for(int i = 0; i < range.size(); i++) {
		for (int col = range[i].leftColumn(); col <= range[i].rightColumn(); col++)
 			if (columns.indexOf(col) == -1) columns.push_back(col);
			
		for(int row = range[i].topRow(); row <= range[i].bottomRow(); row++)
			if (rows_n.indexOf(row) == -1) rows_n.push_back(row);
			
		if (!UpdateProgress(progress, i)) return false;	
	}
	
// sort	
	progress.setLabelText(tr("Sorting"));
	progress.setMaximum(2);
	progress.setValue(0);
	qSort(columns.begin(), columns.end());
	qSort(rows_n.begin(), rows_n.end());

// add
	progress.setLabelText(tr("Adding rows & columns"));
	progress.setMaximum(rows_n.size());
	progress.setValue(0);
	QList<QStringList> rows;
	for(int i = 0; i < rows_n.size(); i++) {	
		if (!UpdateProgress(progress, i)) return false;	
		QStringList row;
		for (int j = 0; j < columns.size(); j++)	{
 			if (is_item_in_list_selection_range(range, rows_n[i], columns[j])) {
				if (isError_in_cell(rows_n[i], columns[j]))
					return false;
				if (item(rows_n[i], columns[j])) 
 					row.push_back(text(rows_n[i], columns[j]));
			}
		}	
		
		if (row.size() == columns.size() && row.size() > 0)
			rows.push_back(row);
		else {
			rows_n.removeOne(rows_n[i]);
			i--;
		}
		row.clear();
	}
	
	QList<QStringList> temp = rows;		
	qStableSort(rows.begin(), rows.end(), compare);
	if (rows == temp) return false;

// set items
	progress.setLabelText(tr("Setting Items"));
	progress.setMaximum(rows.size());
	progress.setValue(0);
	for (int i = 0; i < rows.size(); i++) {
		if (!UpdateProgress(progress, i)) return false;	
		for(int j = 0; j < rows[i].size(); j++)	
			setItem(rows_n[i], columns[j], rows[i][j]);
	}
 
	return true;
}

 progress.setProgress(it);
.. 
 qApp->processEvents();
 if (progress.wasCanceled()) { 
      return false; 
 }