perf(grids): rebuild media grids on width change, not every scroll tick

2026-06-12 07:18:34 +02:00
parent 2b34f4a9d7
commit 03c623e8c7
9 changed files with 359 additions and 149 deletions
@@ -0,0 +1,69 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:plezy/widgets/sliver_cross_axis_layout_builder.dart';
+
+void main() {
+  testWidgets('builder runs on width change and widget update, never from scrolling', (tester) async {
+    var builderCalls = 0;
+    var firstItemBuilds = 0;
+    double? lastExtent;
+
+    Widget app(double width) => MaterialApp(
+      home: Center(
+        child: SizedBox(
+          width: width,
+          height: 400,
+          child: CustomScrollView(
+            slivers: [
+              SliverCrossAxisLayoutBuilder(
+                builder: (context, crossAxisExtent) {
+                  builderCalls++;
+                  lastExtent = crossAxisExtent;
+                  return SliverList.builder(
+                    itemCount: 100,
+                    itemBuilder: (context, index) {
+                      if (index == 0) {
+                        return Builder(
+                          builder: (context) {
+                            firstItemBuilds++;
+                            return const SizedBox(height: 50);
+                          },
+                        );
+                      }
+                      return const SizedBox(height: 50);
+                    },
+                  );
+                },
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    await tester.pumpWidget(app(300));
+    expect(builderCalls, 1);
+    expect(lastExtent, 300);
+    expect(firstItemBuilds, 1);
+
+    // Scrolling changes SliverConstraints.scrollOffset but not the cross-axis
+    // extent: the builder must not re-run, and the realized first item (still
+    // within the cache extent) must not be rebuilt.
+    await tester.drag(find.byType(CustomScrollView), const Offset(0, -30));
+    await tester.pumpAndSettle();
+    expect(builderCalls, 1, reason: 'scrolling must not re-invoke the builder');
+    expect(firstItemBuilds, 1, reason: 'scrolling must not rebuild realized children');
+
+    // A real width change re-runs the builder with the new extent.
+    await tester.pumpWidget(app(250));
+    await tester.pumpAndSettle();
+    expect(builderCalls, 2);
+    expect(lastExtent, 250);
+
+    // Updating the widget (new builder closure from a parent rebuild) re-runs
+    // it even at the same width — data changes must always propagate.
+    await tester.pumpWidget(app(250));
+    await tester.pumpAndSettle();
+    expect(builderCalls, 3);
+  });
+}