LateInitializationError in initialization of Stateful Widget

Question

In my mobile application, I am initializing a Stateful widget from another widget but I always get an exception

[ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: LateInitializationError: Field '_customAppLoaderState@64195267' has not been initialized

Below is the code for custom_loader.dart

import 'package:SMedoApp/util/app_textstyles.dart';
import 'package:SMedoApp/util/color_constants.dart';
import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
import 'package:flutter_spinkit/flutter_spinkit.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';

class CustomAppLoader extends StatefulWidget {
  // const CustomAppLoader({Key? key}) : super(key: key);
  late final _CustomAppLoaderState _customAppLoaderState;

  @override
  State<CustomAppLoader> createState() {
    _customAppLoaderState=_CustomAppLoaderState();
    return _customAppLoaderState;
  }

  void setLoaderVisible(bool _visibility){
    _customAppLoaderState.setVisibility(_visibility);
  }

  void setProgressPerc(double progress){
    _customAppLoaderState.setProgressValue(progress: progress);
  }

  void setCancelToken(CancelToken cancelToken) {
    _customAppLoaderState.setCancelToken(cancelToken: cancelToken);
  }
}

class _CustomAppLoaderState extends State<CustomAppLoader> {

  bool isLoaderVisible=false;
  double _progress=0.0;
  CancelToken? _cancelToken;
  bool isCancelButtonVisible=false;

  @override
  Widget build(BuildContext context) {
    return Visibility(
      visible: isLoaderVisible,
      child: Center(
        child: Container(
            color: ColorConstants.black.withOpacity(0.8),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                SpinKitWave(
                    size: 50,
                    color: ColorConstants.white,
                    type: SpinKitWaveType.start
                ),
                SizedBox(
                  height: 50,
                ),
                Container(
                  width: 200,
                  child: LinearProgressIndicator(
                    backgroundColor: ColorConstants.white,
                    valueColor: new AlwaysStoppedAnimation<Color>(ColorConstants.facebook_blue),
                    value: _progress,
                    minHeight: 2,
                  ),
                ),
                SizedBox(
                  height: 10,
                ),
                Visibility(
                  visible: isCancelButtonVisible,
                  child: TextButton(onPressed: (){
                    _cancelToken?.cancel();
                    if(_cancelToken!.isCancelled)
                      Navigator.pop(context);
                  }, child: Text(AppLocalizations.of(context)!.cancel, style: AppTextStyle.whiteOnBlackSmallWhite(context),), ),
                )
              ],
            )),
      ),
    );
  }

  void setVisibility(bool _visibility){
    setState(() {
      isLoaderVisible=_visibility;
    });
  }

  void setProgressValue({required double progress}) {
    setState(() {
        _progress=progress;
      }
    );
  }

  void setCancelToken({required CancelToken cancelToken}) {
    setState(() {
      _cancelToken=cancelToken;
      isCancelButtonVisible=true;
    });
  }
}

And this is how I invoke custom_loader from another widget

CustomAppLoader loader=CustomAppLoader();
loader.setProgressPerc(0.25);

Where am I going wrong? (I am new to flutter/ dart).

Answer 1

createState() is not called yet on initialization of the CustomAppLoader, so when you call setProgressPerc the state doesn't exist yet. It's also not really common to save the state in a variable and using it like that.

My IDE also actually suggest that you shouldn't do any logic in the createState():