QCompleter for large models

Question

QCompleter works slightly slow on large data sets (large models): when I start to input characters in QCombobox it passes few seconds to show auto-

Answer 1

Solution appears similar to this: https://stackoverflow.com/a/33404207/630169 as QCompleter also uses QListView in its popup(). So full solution to speed-up QCombobox is:

Tweak combo:

void ComboboxTools::tweak(QComboBox *combo)
{
  //  For performance reasons use this policy on large models
  // or AdjustToMinimumContentsLengthWithIcon
  combo->setSizeAdjustPolicy(QComboBox::AdjustToMinimumContentsLength);

  // Improve combobox view performance
  tweak((QListView *)combo->view());

  // Improve combobox completer performance
  tweak(combo->completer());
}

Tweak dropdown/popup (view):

void ComboboxTools::tweak(QListView *view)
{
  // Improving Performance:  It is possible to give the view hints
  // about the data it is handling in order to improve its performance
  // when displaying large numbers of items. One approach that can be taken
  // for views that are intended to display items with equal sizes
  // is to set the uniformItemSizes property to true.
  view->setUniformItemSizes(true);
  // This property holds the layout mode for the items. When the mode is Batched,
  // the items are laid out in batches of batchSize items, while processing events.
  // This makes it possible to instantly view and interact with the visible items
  // while the rest are being laid out.
  view->setLayoutMode(QListView::Batched);
  // batchSize : int
  // This property holds the number of items laid out in each batch
  // if layoutMode is set to Batched. The default value is 100.
  // view->setBatchSize(100);
}

Tweak completer:

void ComboboxTools::tweak(QCompleter *completer)
{
  completer->setCaseSensitivity(Qt::CaseInsensitive);
  // If the model's data for the completionColumn() and completionRole() is sorted
  // in ascending order, you can set ModelSorting property
  // to CaseSensitivelySortedModel or CaseInsensitivelySortedModel.
  // On large models, this can lead to significant performance improvements
  // because the completer object can then use a binary search algorithm
  // instead of linear search algorithm.
  completer->setModelSorting(QCompleter::CaseSensitivelySortedModel);

  // Improve completer popup (view) performance
  tweak((QListView *)completer->popup());
}