improve page loading

lib/sheet_viewer_page.dart

@@ -9,8 +9,11 @@ class SheetViewerPage extends StatefulWidget {
   final Sheet sheet;
   final ApiClient apiClient;
 
-  const SheetViewerPage(
-      {super.key, required this.sheet, required this.apiClient});
+  const SheetViewerPage({
+    super.key,
+    required this.sheet,
+    required this.apiClient,
+  });
 
   @override
   State<SheetViewerPage> createState() => _SheetViewerPageState();
@@ -21,11 +24,13 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
   int page = 1;
   int numPages = 1;
   bool isFullscreen = false;
+  late Future<bool> documentLoaded;
   PdfDocument? document;
 
   @override
   void initState() {
     super.initState();
+    documentLoaded = loadPdf();
   }
 
   @override
@@ -34,15 +39,15 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
     super.dispose();
   }
 
-  Future<PdfDocument> loadPdf() async {
+  Future<bool> loadPdf() async {
     var file = await widget.apiClient.getPdfFileCached(widget.sheet.uuid);
     if (file == null) {
       throw Exception("Failed fetching pdf file");
     }
 
-    var document = await PdfDocument.openFile(file.path);
+    document = await PdfDocument.openFile(file.path);
 
-    return document;
+    return true;
   }
 
   void toggleFullscreen() {
@@ -50,30 +55,30 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
     if (isFullscreen) {
       log.info("enter fullscreen");
       // enter fullscreen
-      SystemChrome.setEnabledSystemUIMode(SystemUiMode.immersiveSticky,
-          overlays: []);
+      SystemChrome.setEnabledSystemUIMode(
+        SystemUiMode.immersiveSticky,
+        overlays: [],
+      );
     } else {
       // exit fullscreen
       log.info("exit fullscreen");
-      SystemChrome.setEnabledSystemUIMode(SystemUiMode.edgeToEdge,
-          overlays: SystemUiOverlay.values);
+      SystemChrome.setEnabledSystemUIMode(
+        SystemUiMode.edgeToEdge,
+        overlays: SystemUiOverlay.values,
+      );
     }
   }
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(
-        title: Text(widget.sheet.name),
-      ),
+      appBar: AppBar(title: Text(widget.sheet.name)),
       body: FutureBuilder(
-          future: loadPdf(),
-          builder: (BuildContext context, AsyncSnapshot<PdfDocument> snapshot) {
-            if (snapshot.hasData) {
-              document = snapshot.data;
-              if (document != null) {
+        future: documentLoaded,
+        builder: (BuildContext context, AsyncSnapshot<bool> snapshot) {
+          if (snapshot.hasData && document != null) {
             numPages = document!.pages.length;
-              }
+
             return GestureDetector(
               onTapUp: (TapUpDetails details) {
                 // Get the size of the screen
@@ -100,7 +105,10 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
                   });
                 }
               },
-                child: Stack(
+              child: Row(
+                mainAxisAlignment: MainAxisAlignment.center,
+                children: [
+                  Stack(
                     children: [
                       PdfPageView(
                         key: ValueKey(page),
@@ -115,20 +123,30 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
                       ),
                     ],
                   ),
+                  // PdfPageView(
+                  //   key: ValueKey(page),
+                  //   document: document,
+                  //   pageNumber: page + 1,
+                  //   alignment: Alignment.center,
+                  // ),
+                ],
+              ),
             );
           } else if (snapshot.hasError) {
             return Center(
               child: Text(
-                      style: Theme.of(context)
-                          .textTheme
-                          .displaySmall!
-                          .copyWith(color: Colors.red),
+                style: Theme.of(
+                  context,
+                ).textTheme.displaySmall!.copyWith(color: Colors.red),
                 textAlign: TextAlign.center,
-                      snapshot.error.toString()));
+                snapshot.error.toString(),
+              ),
+            );
           } else {
             return const Center(child: CircularProgressIndicator());
           }
-          }),
+        },
+      ),
     );
   }
 }