这是来自Bloc architecture "the getter x was called on null."的直接后续内容，该问题已由@nonybrighto解决
现在的问题是，尽管我再也没有从应用程序中收到任何错误，但是由于颜色没有更新，因此逻辑在某处失败了，它们只是保持蓝色。如果我调用：colorBloc.changeColor（）;从回调到子项本身（下拉菜单），或者直接从父项进行回调，它实际上并没有更新这些小部件按钮的颜色。它们总是蓝色。
要让按钮小部件实际更新，还需要做些其他事情吗？
是否需要其他信息？
编辑：父类和子类，以及我如何使用块。
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 = ColorBloc();
@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,
),
));
super.initState();
}
@override
dispose() {
_animationController.dispose();
colorBloc.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> [
BlocProvider(
bloc: ColorBloc(),
child: 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');
} : () {},
),
),
),
],
),
],
);
}
}
singleplayer.dart
import 'dart:async';
import 'dart:io';
import 'package:flutter/material.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();
@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: Container(
child: Row(
children: <Widget> [
FloatingActionButton(
backgroundColor: Colors.blue,
heroTag: null,
onPressed: _changeColourButton,
child: Text(
'change',
),
),
dropDownMenu(
singlePlayerCallbacks: callBacks,
),
],
),
),
),
);
}
}
基本上，这就是我要尝试的方式。
答案 0 :(得分：1)
我对代码中的注释进行了一些修改。无法对其进行测试以确保其正常工作，因此请尝试一下。
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');
} : () {},
),
),
),
],
),
],
);
}
}
答案 1 :(得分：0)
我要删除 colorBloc = BlocProvider.of（context）; 并声明最终的colorBloc = ColorBloc;外部主要方法奏效。其余的都是一样的。 注意：我正在使用generic_bloc_provider 注意*：这不是最佳方法。