Add image pinch-to-zoom and PDF scroll rendering
epic-document-attachments-ui-task-004 — Extend AttachmentPreviewModal with InteractiveViewer for pinch-to-zoom on JPEG/PNG content loaded via signed URL, and a scrollable PDF rendering widget (e.g., flutter_pdfview or syncfusion_flutter_pdfviewer) for PDF content. Add graceful error state widget when content fails to load.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Implement a _buildContent(String mimeType, String signedUrl) factory method inside AttachmentPreviewModal that returns the appropriate child widget based on mimeType. Use a switch on mimeType: 'image/jpeg' | 'image/png' → ImagePreviewWidget; 'application/pdf' → PdfPreviewWidget; default → UnsupportedTypeWidget. For ImagePreviewWidget, use CachedNetworkImage with a loadingBuilder (show placeholder) and errorBuilder (show error state). Wrap it in InteractiveViewer with minScale: 0.5, maxScale: 4.0, clipBehavior: Clip.none.
For PdfPreviewWidget, if using flutter_pdfview, pass the signed URL to PDFView(filePath: ...) after downloading to a temp file with http package or dio, then delete the file in dispose(). If using syncfusion_flutter_pdfviewer, SfPdfViewer.network(signedUrl) is simpler but requires a license for commercial use — confirm with the team. Wrap the entire content area in AnimatedSwitcher with a FadeTransition for smooth loading→content animation.
Testing Requirements
Widget tests: verify InteractiveViewer is in the tree when mimeType is image/jpeg or image/png; verify PDF viewer widget is in the tree when mimeType is application/pdf; verify error state widget appears when image loader throws (use a mocked image provider); verify error state widget appears for unsupported mimeType; verify retry button in error state triggers reload. Integration test (optional, TestFlight): manually verify pinch-to-zoom on a real device. Unit test: mimeType routing function — given each mimeType, returns correct ContentRenderStrategy enum value.
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.