filterCallback property

FilterCallback<T>? filterCallback
final

When DropdownMenu.enableFilter is true, this callback is used to compute the list of filtered items.

In this example the filterCallback returns the items that contains the trimmed query.
link 
DropdownMenu<Text>(
  enableFilter: true,
  filterCallback: (List<DropdownMenuEntry<Text>> entries, String filter) {
    final String trimmedFilter = filter.trim().toLowerCase();
      if (trimmedFilter.isEmpty) {
        return entries;
      }

      return entries
        .where((DropdownMenuEntry<Text> entry) =>
          entry.label.toLowerCase().contains(trimmedFilter),
        )
        .toList();
  },
  dropdownMenuEntries: const <DropdownMenuEntry<Text>>[],
)

Defaults to null. If this parameter is null and the DropdownMenu.enableFilter property is set to true, the default behavior will return a filtered list. The filtered list will contain items that match the text provided by the input field, with a case-insensitive comparison. When this is not null, enableFilter must be set to true.

Implementation

final FilterCallback<T>? filterCallback;