split file_viewer into focused sub-widgets

lib/widget/file_viewer/deferred_pdf_viewer.dart

@@ -0,0 +1,53 @@
+import 'dart:io';
+
+import 'package:flutter/material.dart';
+import 'package:syncfusion_flutter_pdfviewer/pdfviewer.dart';
+
+import '../app_progress_indicator.dart';
+
+/// SfPdfViewer asserts on `localToGlobal` if mounted during the page-push
+/// animation. Defer until the route enter animation completes.
+class DeferredPdfViewer extends StatefulWidget {
+  const DeferredPdfViewer({super.key, required this.path});
+  final String path;
+
+  @override
+  State<DeferredPdfViewer> createState() => _DeferredPdfViewerState();
+}
+
+class _DeferredPdfViewerState extends State<DeferredPdfViewer> {
+  bool _ready = false;
+  Animation<double>? _routeAnimation;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    if (_ready || _routeAnimation != null) return;
+    final animation = ModalRoute.of(context)?.animation;
+    if (animation == null || animation.isCompleted) {
+      _ready = true;
+      return;
+    }
+    _routeAnimation = animation..addStatusListener(_onAnimationStatus);
+  }
+
+  void _onAnimationStatus(AnimationStatus status) {
+    if (status == AnimationStatus.completed && mounted) {
+      setState(() => _ready = true);
+    }
+  }
+
+  @override
+  void dispose() {
+    _routeAnimation?.removeStatusListener(_onAnimationStatus);
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (!_ready) {
+      return const Center(child: AppProgressIndicator.large());
+    }
+    return SfPdfViewer.file(File(widget.path));
+  }
+}