Get uncaught null check error when trying to modify widget tree

[pckimlong]

As an example

class Example extends StatefulWidget {
  const Example({super.key, required this.path});

  final String path;

  @override
  State<Example> createState() => _ExampleState();
}

class _ExampleState extends State<Example> {
  final controller = PdfViewerController();
  bool darkMode = false;

  @override
  Widget build(BuildContext context) {
    Widget pdfWidget = PdfViewer.file(widget.path, controller: controller);

    if (darkMode) {
      pdfWidget = ColorFiltered(
        colorFilter: const ColorFilter.mode(Colors.white, BlendMode.difference),
        child: pdfWidget,
      );
    }

    return Scaffold(
      appBar: AppBar(
        title: const Text('TEST'),
        actions: [
          IconButton(
            onPressed: () => setState(() => darkMode = !darkMode),
            icon: const Icon(Icons.dark_mode),
          ),
        ],
      ),
      body: pdfWidget,
    );
  }
}

This is the error:
E/flutter (30841): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Null check operator used on a null value E/flutter (30841): #0 PdfViewerController.goToPage (package:pdfrx/src/widgets/pdf_viewer.dart:1020:19) E/flutter (30841): #1 _PdfViewerState.build.<anonymous closure>.<anonymous closure> (package:pdfrx/src/widgets/pdf_viewer.dart:372:26) E/flutter (30841): #2 new Future.microtask.<anonymous closure> (dart:async/future.dart:280:37) E/flutter (30841): #3 _microtaskLoop (dart:async/schedule_microtask.dart:40:21) E/flutter (30841): #4 _startMicrotaskLoop (dart:async/schedule_microtask.dart:49:5) E/flutter (30841): I/flutter (30841): ┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── I/flutter (30841): │ Null check operator used on a null value I/flutter (30841): ├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄ I/flutter (30841): │ 08:18:00.958 (+0:00:21.649522) I/flutter (30841): ├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄ I/flutter (30841): │ ⛔ Uncaught flutter error I/flutter (30841): └─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── I/flutter (30841): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════ I/flutter (30841): The following _TypeError was thrown during paint(): I/flutter (30841): Null check operator used on a null value I/flutter (30841): I/flutter (30841): The relevant error-causing widget was: I/flutter (30841): PdfViewer I/flutter (30841): PdfViewer:file:///Users/kim/Development/projects/freelance/books_5000/lib/src/presentation/modules/book/viewer/book_viewer_page.dart:116:34 I/flutter (30841): I/flutter (30841): When the exception was thrown, this was the stack: I/flutter (30841): #0 PdfViewerController.viewSize (package:pdfrx/src/widgets/pdf_viewer.dart:874:30) I/flutter (30841): #1 PdfViewerController.visibleRect (package:pdfrx/src/widgets/pdf_viewer.dart:887:49) I/flutter (30841): #2 _PdfViewerState._getCacheExtentRect (package:pdfrx/src/widgets/pdf_viewer.dart:666:38) I/flutter (30841): #3 _PdfViewerState._customPaint (package:pdfrx/src/widgets/pdf_viewer.dart:707:24) I/flutter (30841): #4 _CustomPainter.paint (package:pdfrx/src/widgets/pdf_viewer.dart:1296:62) I/flutter (30841): #5 RenderCustomPaint._paintWithPainter (package:flutter/src/rendering/custom_paint.dart:588:13) I/flutter (30841): #6 RenderCustomPaint.paint (package:flutter/src/rendering/custom_paint.dart:635:7) I/flutter (30841): #7 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #8 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #9 RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:129:13) I/flutter (30841): #10 PaintingContext.pushTransform (package:flutter/src/rendering/object.dart:687:14) I/flutter (30841): #11 RenderTransform.paint (package:flutter/src/rendering/proxy_box.dart:2529:27) I/flutter (30841): #12 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #13 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #14 RenderShiftedBox.paint (package:flutter/src/rendering/shifted_box.dart:74:15) I/flutter (30841): #15 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #16 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #17 RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:129:13) I/flutter (30841): #18 PaintingContext.pushClipRect.<anonymous closure> (package:flutter/src/rendering/object.dart:549:83) I/flutter (30841): #19 ClipContext._clipAndPaint (package:flutter/src/painting/clip.dart:25:12) I/flutter (30841): #20 ClipContext.clipRectAndPaint (package:flutter/src/painting/clip.dart:53:5) I/flutter (30841): #21 PaintingContext.pushClipRect (package:flutter/src/rendering/object.dart:549:7) I/flutter (30841): #22 RenderClipRect.paint (package:flutter/src/rendering/proxy_box.dart:1532:25) I/flutter (30841): #23 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #24 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #25 RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:129:13) I/flutter (30841): #26 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #27 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #28 RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:129:13) I/flutter (30841): #29 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #30 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #31 RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:129:13) I/flutter (30841): #32 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #33 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #34 RenderBoxContainerDefaultsMixin.defaultPaint (package:flutter/src/rendering/box.dart:2882:15) I/flutter (30841): #35 RenderStack.paintStack (package:flutter/src/rendering/stack.dart:640:5) I/flutter (30841): #36 RenderStack.paint (package:flutter/src/rendering/stack.dart:656:7) I/flutter (30841): #37 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #38 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #39 RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:129:13) I/flutter (30841): #40 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #41 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #42 _RenderColoredBox.paint (package:flutter/src/widgets/basic.dart:7813:15) I/flutter (30841): #43 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #44 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13) I/flutter (30841): #45 _RenderLayoutBuilder.paint (package:flutter/src/widgets/layout_builder.dart:333:15) I/flutter (30841): #46 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3208:7) I/flutter (30841): #47 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:250:13)

Noted that this error occurred only when using controller, If I don't apply controller, it'll worked just fine

[espresso3389]

How about to change the way ColorFiltered is toggled:

class _ExampleState extends State<Example> {
  final controller = PdfViewerController();
  bool darkMode = false;

  @override
  Widget build(BuildContext context) {
    final pdfWidget = ColorFiltered(
      colorFilter: ColorFilter.mode(
          Colors.white, darkMode ? BlendMode.difference : BlendMode.dst),
      child: PdfViewer.file(widget.path, controller: controller),
    );

    return Scaffold(
      appBar: AppBar(
        title: const Text('TEST'),
        actions: [
          IconButton(
            onPressed: () => setState(() => darkMode = !darkMode),
            icon: const Icon(Icons.dark_mode),
          ),
        ],
      ),
      body: pdfWidget,
    );
  }
}

[espresso3389]

Basically, this is the issue with PdfViewer itself (controller does not wait for widget recreated) but if you keep the parent structure, or keep the PdfViewer widget by some other mechanism such as GlobalKey, the problem is gone.

[espresso3389]

Other change proposals from GitHub Copilot (I'm not tested yet):

class _ExampleState extends State<Example> {
  final controller = PdfViewerController();
  bool darkMode = false;
  late final Widget pdfWidget;

  @override
  void initState() {
    super.initState();
    pdfWidget = PdfViewer.uri(widget.uri, controller: controller);
  }

  @override
  Widget build(BuildContext context) {
    Widget currentWidget = pdfWidget;

    if (darkMode) {
      currentWidget = ColorFiltered(
        colorFilter: const ColorFilter.mode(Colors.white, BlendMode.difference),
        child: currentWidget,
      );
    }

    return Scaffold(
      appBar: AppBar(
        title: const Text('TEST'),
        actions: [
          IconButton(
            onPressed: () => setState(() => darkMode = !darkMode),
            icon: const Icon(Icons.dark_mode),
          ),
        ],
      ),
      body: currentWidget,
    );
  }
}

class _ExampleState extends State<Example> {
  final controller = PdfViewerController();
  final ValueNotifier<bool> darkMode = ValueNotifier(false);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('TEST'),
        actions: [
          IconButton(
            onPressed: () => darkMode.value = !darkMode.value,
            icon: const Icon(Icons.dark_mode),
          ),
        ],
      ),
      body: ValueListenableBuilder<bool>(
        valueListenable: darkMode,
        builder: (context, darkModeValue, child) {
          return darkModeValue
              ? ColorFiltered(
                  colorFilter: const ColorFilter.mode(
                      Colors.white, BlendMode.difference),
                  child: child,
                )
              : child!;
        },
        child: PdfViewer.uri(widget.uri, controller: controller),
      ),
    );
  }
}

[espresso3389]

@pckimlong
On 1227b0f, I've added note about dark/night mode support on README.md; that is based on your code. Thanks so much!