refactor: RemoteParameter class to improve listener

management

packages/flutterfire_remote_parameter_fetcher/lib/src/remote_parameter.dart

@@ -1,16 +1,16 @@
+import 'dart:async';
+
 /// A class that holds the value of a parameter fetched from a remote.
 /// It also provides a Stream of updated parameter information.
 class RemoteParameter<T> {
   RemoteParameter({
     required T value,
-    required Stream<void> onConfigUpdated,
+    required this.onConfigUpdated,
     required this.activateAndRefetch,
-  }) : _value = value {
-    onConfigUpdated.listen((_) async {
-      _value = await activateAndRefetch();
-      _notifyListeners();
-    });
-  }
+  }) : _value = value;
+
+  /// A Stream of updated parameter information.
+  Stream<void> onConfigUpdated;
 
   /// A function that will activate the fetched config and refetch the value.
   /// This is useful for when you want to force a refetch of the value.
@@ -22,10 +22,32 @@ class RemoteParameter<T> {
 
   final List<void Function(T value)> _listeners = [];
 
+  late StreamSubscription<void> _subscription;
+
   /// Add a listener to be notified when the value changes.
   /// Executed when the remote value is updated.
   void addListener(void Function(T value) listener) {
     _listeners.add(listener);
+
+    if (_listeners.length == 1) {
+      // When the listener is added for the first time,
+      // monitor the onConfigUpdated stream.
+      _subscription = onConfigUpdated.listen((_) async {
+        _value = await activateAndRefetch();
+        _notifyListeners();
+      });
+    }
+  }
+
+  /// Remove a listener.
+  Future<void> removeListener(void Function(T value) listener) async {
+    _listeners.remove(listener);
+
+    if (_listeners.isEmpty) {
+      // When the last listener is removed,
+      // cancel the subscription to the onConfigUpdated stream.
+      await _subscription.cancel();
+    }
   }
 
   void _notifyListeners() {

packages/flutterfire_remote_parameter_fetcher/test/src/remote_parameter_test.dart

@@ -38,6 +38,31 @@ void main() {
       expect(rp.value, 20);
     });
 
+    test('should not call listener when removed', () async {
+      final controller = StreamController<void>();
+      addTearDown(controller.close);
+
+      final rp = RemoteParameter<int>(
+        value: 10,
+        onConfigUpdated: controller.stream,
+        activateAndRefetch: () async => 20,
+      );
+
+      var updatedValue = 10;
+      void listener(int value) {
+        updatedValue = value;
+      }
+
+      rp.addListener(listener);
+
+      await rp.removeListener(listener);
+      controller.add(null);
+      await Future<void>.delayed(Duration.zero);
+
+      expect(rp.value, 10);
+      expect(updatedValue, 10);
+    });
+
     test('should refetch value when config updates', () async {
       final controller = StreamController<void>();
       addTearDown(controller.close);
@@ -50,7 +75,7 @@ void main() {
           refetchCalled = true;
           return 20;
         },
-      );
+      )..addListener((_) {});
 
       controller.add(null);