Feature: ability to use nullable listener in useListenableSelector (#377)

Author: JWo1F

packages/flutter_hooks/lib/src/listenable_selector.dart

@@ -25,7 +25,7 @@ part of 'hooks.dart';
 ///
 
 R useListenableSelector<R>(
-  Listenable listenable,
+  Listenable? listenable,
   R Function() selector,
 ) {
   return use(_ListenableSelectorHook(listenable, selector));
@@ -34,7 +34,7 @@ R useListenableSelector<R>(
 class _ListenableSelectorHook<R> extends Hook<R> {
   const _ListenableSelectorHook(this.listenable, this.selector);
 
-  final Listenable listenable;
+  final Listenable? listenable;
   final R Function() selector;
 
   @override
@@ -49,7 +49,7 @@ class _ListenableSelectorHookState<R>
   @override
   void initHook() {
     super.initHook();
-    hook.listenable.addListener(_listener);
+    hook.listenable?.addListener(_listener);
   }
 
   @override
@@ -63,8 +63,8 @@ class _ListenableSelectorHookState<R>
     }
 
     if (hook.listenable != oldHook.listenable) {
-      oldHook.listenable.removeListener(_listener);
-      hook.listenable.addListener(_listener);
+      oldHook.listenable?.removeListener(_listener);
+      hook.listenable?.addListener(_listener);
       _selectorResult = hook.selector();
     }
   }
@@ -83,7 +83,7 @@ class _ListenableSelectorHookState<R>
 
   @override
   void dispose() {
-    hook.listenable.removeListener(_listener);
+    hook.listenable?.removeListener(_listener);
   }
 
   @override

packages/flutter_hooks/test/use_listenable_selector_test.dart

@@ -85,6 +85,38 @@ void main() {
     listenable.dispose();
   });
 
+  testWidgets('null as Listener', (tester) async {
+    const notFoundValue = -1;
+    final testListener = ValueNotifier(false);
+    final listenable = ValueNotifier(777);
+    var result = 0;
+
+    await tester.pumpWidget(
+      HookBuilder(
+        builder: (context) {
+          final shouldUseListener = useListenableSelector(testListener, () {
+            return testListener.value;
+          });
+
+          final actualListener = shouldUseListener ? listenable : null;
+
+          result = useListenableSelector(actualListener, () {
+            return actualListener?.value ?? notFoundValue;
+          });
+
+          return Container();
+        },
+      ),
+    );
+
+    expect(result, notFoundValue);
+    testListener.value = true;
+
+    await tester.pump();
+
+    expect(result, listenable.value);
+  });
+
   testWidgets('update selector', (tester) async {
     final listenable = ValueNotifier(0);
     var isOdd = false;