TF-4425 Fix load more not triggered on iOS 18 when fast scrolling to bottom (#4428)

2026-04-08 10:06:49 +07:00
parent 2a3325ab7a
commit 20f59da386
3 changed files with 51 additions and 4 deletions
@@ -0,0 +1,43 @@
+# 0075. Fix load more not triggered on iOS when fast scrolling to bottom
+
+Date: 2026-03-31
+
+## Status
+
+- Issues:
+  - [TF-4425 Bug: load more is not working](https://github.com/linagora/tmail-flutter/issues/TF-4425)
+
+## Context
+
+On iOS, `handleLoadMoreEmailsRequest()` was never triggered when users scrolled to the bottom of the email list. The original condition used exact equality:
+
+```dart
+scrollInfo.metrics.pixels == scrollInfo.metrics.maxScrollExtent
+```
+
+**Root cause:** iOS uses `BouncingScrollPhysics` (spring-based simulation), which causes `pixels` to either overshoot or settle slightly short of `maxScrollExtent` depending on scroll speed and device performance. In both cases, `ScrollEndNotification` fires when `pixels != maxScrollExtent`, so the condition is never satisfied.
+
+This behavior is device-dependent — newer/faster devices (iPhone 13 Pro Max, iOS 18) are less affected, while older/slower devices (iPhone 7, iOS 15) exhibit larger deviations. Android is unaffected because `ClampingScrollPhysics` clamps `pixels` exactly within `[0, maxScrollExtent]`.
+
+## Decision
+
+Apply `ClampingScrollPhysics` on iOS only, and replace `==` with `>=`:
+
+```dart
+// physics
+physics: PlatformInfo.isIOS
+    ? const ClampingScrollPhysics()
+    : const AlwaysScrollableScrollPhysics(),
+
+// condition
+scrollInfo.metrics.pixels >= scrollInfo.metrics.maxScrollExtent
+```
+
+`ClampingScrollPhysics` ensures `pixels` is clamped exactly to `maxScrollExtent` at the boundary, making the condition deterministic. The `>=` adds a defensive guard for any residual edge cases.
+
+## Consequences
+
+- Load more works correctly across all iOS versions and device generations.
+- No behavior change on Android or Web.
+- iOS loses the native bounce feel at list boundaries. Acceptable for an email list UI.
+- No risk of duplicate requests due to the existing `isRunning` guard.