ブロックストリームが正しく更新されない

コード内のコメントでいくつかの変更を加えました。動作することを確認するためにテストすることはできないので、試してみてください。

SinglePlayer.dart

import 'dart:async';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:tv_series_jokes/blocs/bloc_provider.dart';
import 'package:ultimate_mtg/dropdownmenu.dart';
import 'package:ultimate_mtg/model/colorBloc.dart';

class SinglePlayerMode extends StatefulWidget {
  @override
  SinglePlayerModeParentState createState() => SinglePlayerModeParentState();
}

class SinglePlayerModeParentState extends State<SinglePlayerMode> {

  ColorBloc colorBloc = ColorBloc(); // our color bloc instance

  @override
  void initState() {
    super.initState();
    SystemChrome.setEnabledSystemUIOverlays([]);
    SystemChrome.setPreferredOrientations([DeviceOrientation.landscapeLeft,]);
    Screen.keepOn(true);
  }

  @override
  dispose() {
    colorBloc.dispose();
    super.dispose();
  }

  _changeColourButton() {
    colorBloc.changeColor();
  }

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () => _exitApp(context),
      child: Scaffold(
        body: BlocProvider<ColorBloc>( // DropDownMenu can now access the bloc with this
            bloc: colorBloc,
            child: Container(
          child: Row(
            children: <Widget> [
              FloatingActionButton(
                backgroundColor: Colors.blue,
                heroTag: null,
                onPressed: _changeColourButton,
                child: Text(
                  'change',
                ),
              ),
              dropDownMenu(
                singlePlayerCallbacks: callBacks,
              ),
            ],
          ),
        ),   
        ),
      ),
    );
  }
}  

DropDownMenu.dart

import 'package:flutter/material.dart';
import 'dart:math';
import 'package:ultimate_mtg/model/colorBloc.dart';
import 'package:ultimate_mtg/model/blocprovider.dart';

// ignore: camel_case_types
class dropDownMenu extends StatefulWidget {
  final Function() onPressed;
  final String tooltip;
  final IconData icon;
  final _callback;

  dropDownMenu({Key key, this.onPressed, this.tooltip, this.icon, @required void singlePlayerCallbacks(String callBackType), @required StatefulWidget styleMenu }  ):
      _callback = singlePlayerCallbacks;

  @override
  dropDownMenuState createState() => dropDownMenuState();
}

// ignore: camel_case_types
class dropDownMenuState extends State<dropDownMenu>
    with SingleTickerProviderStateMixin {
  bool isOpened = false;
  AnimationController _animationController;
  Animation<double> _translateButton;
  Curve _curve = Curves.easeOut;
  double _fabHeight = 58;
  double menuButtonSize = 55;
  Color menuButtonTheme;
  ColorBloc colorBloc; // we no longer create the instance here.

  @override
  initState() {
    _animationController =
    AnimationController(vsync: this, duration: Duration(milliseconds: 600))
      ..addListener(() {
        setState(() {});
      });
    _translateButton = Tween<double>(
      begin: 0.0,
      end: _fabHeight,
    ).animate(CurvedAnimation(
      parent: _animationController,
      curve: Interval(
        0.0,
        1.0,
        curve: _curve,
      ),
    ));


    colorBloc = BlocProvider.of<ColorBloc>(context); // Getting the color bloc from the widget tree
    super.initState();
  }

  @override
  dispose() {
    _animationController.dispose();
    super.dispose();
  }

  animate() {
    if (!isOpened) {
      _animationController.forward();
    } else {
      _animationController.reverse();
    }
    isOpened = !isOpened;
  }

  Widget backgroundColour() {
    return StreamBuilder(
      initialData: Colors.blue,
      stream: colorBloc.colorStream,
      builder: (BuildContext context, snapShot) => Container(
        width: menuButtonSize,
        height: menuButtonSize,
        child: RawMaterialButton(
          shape: CircleBorder(),
          fillColor: Colors.black,
          elevation: 5.0,
          onPressed: (){},
          child: Container(
            height: menuButtonSize - 3,
            width: menuButtonSize - 3,
            decoration: BoxDecoration(
              color: snapShot.data,
              shape: BoxShape.circle,
            ),
            child: Image.asset(
              'lib/images/background_colour.png',
              scale: 4,
            ),
          ),
        ),
      ),
    );
  }

  Widget toggle() {
    return Transform.rotate(
      angle: _animationController.value * (pi * 2),
      child: Container(
        width: menuButtonSize,
        height: menuButtonSize,
        child: RawMaterialButton(
          shape: CircleBorder(),
          fillColor: Colors.black,
          elevation: 5.0,
          onPressed: animate,
          child: SizedBox(
            height: menuButtonSize - 3,
            width: menuButtonSize - 3,
            child: Image.asset('lib/images/ic_launcher.png'),
          ),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {

    return Stack(
      children: <Widget> [
       // Removed the BlocProvider widget here. It wasn't working anything and was creating a separate bloc instance
       // I also see why you tried to make us of the blocprovider in the backgroundColour method and it gave null.Couldn't
       // have worked from that context.
       Column(
            mainAxisAlignment: MainAxisAlignment.start,
            children: [
              Stack(
                children: <Widget>[
                  Transform(
                    transform: Matrix4.translationValues(
                      0,
                      _translateButton.value,
                      0,
                    ),
                    child: backgroundColour(),
                  ),
                  toggle(),
                ],
              ),
            ],
        ),
        Column(
          mainAxisAlignment: MainAxisAlignment.start,
          children: <Widget>[
            Container(
              height: menuButtonSize,
              width: menuButtonSize,
              child: Opacity(
                opacity: 0.0,
                child: FloatingActionButton(
                  heroTag: null,
                  onPressed: animate,
                ),
              ),
            ),
            SizedBox(
              height: 3.0,
            ),
            Container(
              height: menuButtonSize,
              width: menuButtonSize,
              child: Opacity(
                opacity: 0.0,
                child: FloatingActionButton(
                  heroTag: null,
                  onPressed:  isOpened == true? (){
                    widget?._callback('background');
                  } : () {},
                ),
              ),
            ),
          ],
        ),
      ],
    );
  }
}