Bloc体系结构“将吸气剂x调用为null". [英] Bloc architecture "the getter x was called on null."
问题描述
根据文档，我正在尝试使用Bloc Architecture设置子小部件的颜色状态，但这是行不通的.这是我的相关文件:
I am trying to use Bloc Architecture to set the Color state of child widgets, according to the documentation, and it just doesn't work. Here are my relevant files:
blocProvider.dart
blocProvider.dart
import 'package:flutter/material.dart';
Type _typeOf<T>() => T;
abstract class BlocBase {
void dispose();
}
class BlocProvider<T extends BlocBase> extends StatefulWidget {
BlocProvider({
Key key,
@required this.child,
@required this.bloc,
}) : super(key: key);
final Widget child;
final T bloc;
@override
_BlocProviderState<T> createState() => _BlocProviderState<T>();
static T of<T extends BlocBase>(BuildContext context) {
final type = _typeOf<_BlocProviderInherited<T>>();
_BlocProviderInherited<T> provider =
context.ancestorInheritedElementForWidgetOfExactType(type)?.widget;
return provider?.bloc;
}
}
class _BlocProviderState<T extends BlocBase> extends State<BlocProvider<T>> {
@override
void dispose() {
widget.bloc?.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return new _BlocProviderInherited<T>(
bloc: widget.bloc,
child: widget.child,
);
}
}
class _BlocProviderInherited<T> extends InheritedWidget {
_BlocProviderInherited({
Key key,
@required Widget child,
@required this.bloc,
}) : super(key: key, child: child);
final T bloc;
@override
bool updateShouldNotify(_BlocProviderInherited oldWidget) => false;
}
colorBloc.dart
colorBloc.dart
import 'dart:async';
import 'package:ultimate_mtg/model/blocprovider.dart';
import 'dart:ui';
import 'dart:math';
class ColorBloc extends BlocBase {
// streams of Color
StreamController streamListController = StreamController<Color>.broadcast();
// sink
Sink get colorSink => streamListController.sink;
// stream
Stream<Color> get colorStream => streamListController.stream;
// function to change the color
changeColor() {
colorSink.add(getRandomColor());
}
@override
dispose() {
streamListController.close();
}
}
// Random Colour generator
Color getRandomColor() {
Random _random = Random();
return Color.fromARGB(
_random.nextInt(256),
_random.nextInt(256),
_random.nextInt(256),
_random.nextInt(256),
);
}
还有我的孩子小部件:
dropdownmenu.dart
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();
super.dispose();
}
animate() {
if (!isOpened) {
_animationController.forward();
} else {
_animationController.reverse();
}
isOpened = !isOpened;
}
Widget backgroundColour() {
colorBloc = BlocProvider.of(context);
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');
} : () {},
),
),
),
],
),
],
);
}
}
我遇到的错误是在backgroundColour()小部件中:
The error I am getting is in the backgroundColour() widget:
Widget backgroundColour() {
colorBloc = BlocProvider.of(context);
return StreamBuilder(
initialData: Colors.blue,
stream: colorBloc.colorStream,
在显示>流的行上:colorBloc.colorStream，
On the line that says > stream: colorBloc.colorStream,
这是日志中的特定错误:
And here is the specific error in the logs:
I/flutter (18865): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (18865): The following NoSuchMethodError was thrown building dropDownMenu(dirty, state:
I/flutter (18865): dropDownMenuState#7edb3(ticker inactive)):
I/flutter (18865): The getter 'colorStream' was called on null.
I/flutter (18865): Receiver: null
I/flutter (18865): Tried calling: colorStream
我已经尽可能地仔细阅读了文档，但是我看不到他们初始化此流的任何地方或任何类似性质的东西.我真的不了解此错误或如何解决它.有人对流有任何经验吗?
I have followed the documentation as closely as I can, but I can't see anywhere they they initialise this stream, or anything of that nature. I am really not understanding this error or how to resolve it. Anyone have any experience with streams?
推荐答案
调用'of'方法时，您没有传递BlocBase子类.
You didn't pass in your BlocBase subclass when calling your 'of' method.
使用colorBloc = BlocProvider.of<ColorBloc>(context);
代替
colorBloc = BlocProvider.of(context);
use colorBloc = BlocProvider.of<ColorBloc>(context);
instead of
colorBloc = BlocProvider.of(context);
再次查看代码，您不需要该行，因为ColorBloc位于当前类中，而不位于小部件树中.只需删除该行即可使用上面的ColorBloc实例.
Looking at the code again, You don't need that line since ColorBloc resides in the current class and not up the widget tree. Just delete that line to make use of the ColorBloc instance above.
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