`useResultRowCountListener`

The useResultRowCountListener hook registers a listener function with a Queries object that will be called whenever the count of ResultRow objects in a ResultTable changes.

useResultRowCountListener(
  queryId: IdOrNull,
  listener: ResultRowCountListener,
  listenerDeps?: DependencyList,
  queriesOrQueriesId?: any,
): void

	Type	Description
`queryId`	`IdOrNull`	The `Id` of the query to listen to, or `null` as a wildcard.
`listener`	`ResultRowCountListener`	The function that will be called whenever the `Row` `Ids` in the matching `ResultTable` change.
`listenerDeps?`	`DependencyList`	An optional array of dependencies for the `listener` function, which, if any change, result in the re-registration of the listener. This parameter defaults to an empty array.
`queriesOrQueriesId?`	`any`	The `Queries` object to register the listener with: omit for the default context `Queries` object, provide an `Id` for a named context `Queries` object, or provide an explicit reference.
returns	`void`	This has no return value.

This hook is useful for situations where a component needs to register its own specific listener to do more than simply tracking the value (which is more easily done with the useResultRowCount hook).

You can either listen to a single ResultTable (by specifying a query Id as the method's first parameter) or changes to any ResultTable (by providing a null wildcard).

Unlike the addResultRowCountListener method, which returns a listener Id and requires you to remove it manually, the useResultRowCountListener hook manages this lifecycle for you: when the listener changes (per its listenerDeps dependencies) or the component unmounts, the listener on the underlying Queries object will be deleted.

Example

This example uses the useResultRowCountListener hook to create a listener that is scoped to a single component. When the component is unmounted, the listener is removed from the Queries object.

const App = ({queries}) => (
  <Provider queries={queries}>
    <Pane />
  </Provider>
);
const Pane = () => {
  useResultRowCountListener('petColors', () =>
    console.log('Result Row count changed'),
  );
  return <span>App</span>;
};

const store = createStore().setTable('pets', {
  fido: {species: 'dog', color: 'brown'},
  felix: {species: 'cat', color: 'black'},
  cujo: {species: 'dog', color: 'black'},
});
const queries = createQueries(store).setQueryDefinition(
  'petColors',
  'pets',
  ({select}) => select('color'),
);
const app = document.createElement('div');
const root = ReactDOMClient.createRoot(app);
root.render(<App queries={queries} />);
console.log(queries.getListenerStats().rowCount);
// -> 1

store.setRow('pets', 'rex', {species: 'dog', color: 'tan'});
// -> 'Result Row count changed'

root.unmount();
console.log(queries.getListenerStats().rowCount);
// -> 0

Since

v4.1.0