fix an issue in which level 1 does not immediately unlock

This happened when the cursor is moved back to level 0 before navigating to
the subpage of level 1. The selector for rebuilding questions was too
restrictive, so that the level 1 questions would never rebuild (and thus
not become visible) in this case.

A workaround for this problem in 1.1.2 is to solve level 0 again, or to
change the theme or reset the progress.

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 
 ## [Unreleased]
+### Fixed
+- an issue in which level 1 did not unlock
+  (Workaround for version 1.1.2: Solve the very first question again or change the theme.)
 
 ## [1.1.2] - 2022-07-22
 ### Added

lib/main.dart

@@ -533,11 +533,18 @@ class ExamsScreen extends StatelessWidget {
           padding: listPadding,
           itemCount: Provider.of<Game>(context, listen: false).levels.length,  // as number of levels is constant, not listening avoids unnecessary rebuilds
           itemBuilder: (context, levelIdx) => Selector<Game, bool>(
-            selector: (context, game) => levelIdx == game.activeLevel && game.inExamScreen,  // isActive
-            shouldRebuild: (bool oldIsActive, bool isActive) => oldIsActive || isActive,
-            builder: (_, isActive, child) {  // we do not use the inner context since world changes (such as theme) would not trigger a rebuild
+            selector: (context, game) {
+              // Rendering exam questions is only relevant when in the exam screen.
+              // This deliberately covers a broad range of questions to avoid missing important rebuilds.
+              // Fortunately, Flutter only renders the questions that are visible on screen.
+              final isRelevant = game.inExamScreen;
+              return isRelevant;
+            },
+            shouldRebuild: (bool oldIsRelevant, bool newIsRelevant) => oldIsRelevant || newIsRelevant,
+            builder: (_, isRelevant, child) {  // we do not use the inner context since world changes (such as theme) would not trigger a rebuild
               final game = Provider.of<Game>(context, listen: false);  // listening not needed, since selector already does
               assert((levelIdx > 0) ^ game.levels[levelIdx].exercise.questions.isEmpty);
+              final isActive = levelIdx == game.activeLevel && game.inExamScreen;
               final level = game.levels[levelIdx];
               final label = 'Level $levelIdx';
               final unlocked = levelIdx <= game.levelsUnlocked || debugUnlockAll;