After filtering, get count of items currently displayed in a Grid widget in Vaadin 14 web app

Question

In the Grid widget of Vaadin 14, backed by a ListDataProvider, after applying a filter(s) via a call such as setFilter or addFilter…

➥ How does one detect how many of the items in the data provider are currently displayed to the user?

I have noticed the ListDataProvider::size method. But that method takes a Query with a SerializablePredicate. My multiple filters have already been successfully applied, and my Grid is showing a subset of the data provider's items. So I do not want to run another query. I want to know the results of the filters already applied.

Answer 1

Pass new Query<>( myDataProvider.getFilter() ) to ListDataProvider::size

ListDataProvider has the method size(Query<T, SerializablePredicate<T>> query).

Because the dataprovider only keeps the original list of items, a simple size method without parameters would not work as you wanted. You can build the required query using the current filters of your dataprovider.

I tested the following code and it works:

// my own method, defined as value change listeners of any filter field
private void onFilterChange(){
    ListDataProvider<Foo> dataProvider = (ListDataProvider<Foo>) grid.getDataProvider();
    dataProvider.setFilter((item) -> {......}

    // everytime after resetting the filter, check how many items now are displayed
    int filteredSize = dataProvider.size(new Query<>(dataProvider.getFilter()));

    int fullSize = dataProvider.getItems().size(); // this is how you get the size of all items
    Notification.show(String.format("Now showing %d of %d items", filteredSize, fullSize));
}

Perhaps in the future this work might be a little easier: See feature-request ticket Add filteredSize method to DataProvider or ListDataProvider #7539.