Build AttachmentThumbnailGrid base widget
epic-document-attachments-ui-task-001 — Implement the AttachmentThumbnailGrid Flutter widget that renders a compact grid within the activity detail view. Display image previews for JPEG/PNG files and document icons for PDF files. Include file name and size subtitles beneath each thumbnail. Wire up to the activity-attachment-repository for data loading.
Acceptance Criteria
Technical Requirements
Implementation Notes
Use a 2-column GridView.builder with childAspectRatio around 0.85 to give space for the subtitle. Determine rendering strategy from attachment.mimeType: if 'image/jpeg' or 'image/png', use CachedNetworkImage (or Image.network) with a BoxFit.cover; if 'application/pdf', show a styled container with an icon. Format file size using a utility: bytes < 1024 → 'X B', < 1048576 → 'X KB', else 'X MB'. Truncate file names with overflow: TextOverflow.ellipsis and maxLines: 1.
Wrap the grid in a Consumer (Riverpod) or BlocBuilder to handle loading/error/data states. Follow the project's design token system for spacing, typography, and color — do not hardcode values. Apply Semantics wrapper to each thumbnail cell with a label combining file name and type.
Testing Requirements
Write widget tests using flutter_test and WidgetTester. Test: grid renders correct number of cells for a list of 3 mock attachments; JPEG attachment shows Image widget; PDF attachment shows document Icon widget; empty list renders empty state widget; loading state renders progress indicator. Use a mocked ActivityAttachmentRepository via Riverpod override or BLoC stub. Accessibility test: verify Semantics labels are present on thumbnail cells.
Flutter does not include a first-party PDF renderer. Third-party packages (e.g., flutter_pdfview, syncfusion_flutter_pdf) have inconsistent accessibility support, may not honour dynamic type scaling, and can introduce large binary size increases. Choosing the wrong package late in development risks rework or an inaccessible PDF experience for Blindeforbundet users.
Mitigation & Contingency
Mitigation: Evaluate and spike two PDF rendering packages (flutter_pdfview and pdfx) in the first task of this epic before committing to implementation. Criteria: VoiceOver compatibility, dynamic type support, APK/IPA size delta, and licence. Document the decision in an ADR.
Contingency: If no package meets accessibility requirements, fall back to opening PDFs in the system browser via url_launcher, which inherits the OS's accessible PDF viewer. Display a clear 'Opening in external viewer' message to set user expectation.
Flutter's Semantics API for live region announcements (analogous to aria-live) has known gaps on Android for dynamic content updates. Upload progress announcements required by the accessibility user story may not fire reliably on Android devices used by HLF and NHF members.
Mitigation & Contingency
Mitigation: Use SemanticsService.announce() for imperative announcements at each upload state transition rather than relying on declarative Semantics widget tree updates. Test on a physical Android device with TalkBack enabled during development, not only on iOS with VoiceOver.
Contingency: If SemanticsService.announce() proves unreliable, implement a persistent accessible status banner at the top of the screen that reflects the current upload state as plain text, satisfying the WCAG success criterion through a visual + programmatic mechanism.
iOS and Android file picker behaviour diverges significantly: MIME type filtering works reliably on Android but is advisory on iOS (users can still navigate to and select non-compliant files via the Files app). This could allow unsupported file types to reach the upload service, causing validation failures with a confusing user experience.
Mitigation & Contingency
Mitigation: Rely on the AttachmentUploadService (Epic 2) as the authoritative MIME validation gate, regardless of platform. In the UI, re-validate the picked file's extension/MIME after selection and show an inline plain-language error ('Only PDF, JPEG, and PNG files are supported') before even calling the service.
Contingency: If users consistently hit the error due to iOS file picker limitations, add a user-facing help tooltip on the picker sheet explaining the supported file types, reducing support volume while the underlying OS limitation persists.
WCAG 2.2 AA compliance for three new interactive components (picker, grid, modal) with file system integration, role-gated actions, and live regions is a significant accessibility surface area. An incomplete audit before release could result in the feature being unusable for Blindeforbundet screen reader users at launch.
Mitigation & Contingency
Mitigation: Allocate a dedicated accessibility audit task at the end of the epic using the accessibility-test-harness (619) and wcag-compliance-checker (620) components already in the project. Include at least one manual test session on a physical device with VoiceOver enabled. Fail the epic's definition of done if any WCAG 2.2 AA violation remains open.
Contingency: If critical accessibility issues are found late, gate the feature behind the org-level attachments_enabled feature flag and only enable it for NHF (the requesting org) after a targeted fix cycle, rather than delaying the release for all organisations.