fix: If builder of Observer errors, further error LateInitializationE…

…rror: Local 'built' has not been initialized. will happen in addition to the actual error, reducing developer experience #780
mobxjs · Mar 22, 2022 · e2954b3 · e2954b3
1 parent b324e5e
commit e2954b3
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Showing 2 changed files with 9 additions and 4 deletions.
diff --git a/flutter_mobx/lib/src/observer_widget_mixin.dart b/flutter_mobx/lib/src/observer_widget_mixin.dart
@@ -114,7 +114,7 @@ mixin ObserverElementMixin on ComponentElement {
 
   @override
   Widget build() {
-    late final Widget built;
+    Widget? built;
 
     reaction.track(() {
       built = super.build();
@@ -128,7 +128,12 @@ mixin ObserverElementMixin on ComponentElement {
       );
     }
 
-    return built;
+    // Better than a "LateInitializationError" which confuses the user, see #780
+    if (built == null) {
+      throw Exception('Error building widget');
+    }
+
+    return built!;
   }
 
   @override

diff --git a/flutter_mobx/test/flutter_mobx_test.dart b/flutter_mobx/test/flutter_mobx_test.dart
@@ -70,7 +70,7 @@ void main() {
   });
 
   testWidgets(
-      'Observer should re-throw exceptions occuring inside the reaction',
+      'Observer should throw exception if exceptions occur inside the reaction',
       (tester) async {
     dynamic exception;
 
@@ -98,7 +98,7 @@ void main() {
 
     expect(tester.firstWidget(find.byWidget(widget)), equals(widget));
 
-    expect(exception, isInstanceOf<Error>());
+    expect(exception.message, 'Error building widget');
   });
 
   testWidgets('Observer should report Flutter errors during invalidation',