在构建过程中调用的setState()或markNeedsBuild()-Flutter

Question

我收到这个错误。调试控制台中可能发生错误的包的链接是下面给出的ResponsiveSafeArea类的生成器函数

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following assertion was thrown building LayoutBuilder:
setState() or markNeedsBuild() called during build.
This _ModalScope<dynamic> widget cannot be marked as needing to build because the framework is
already in the process of building widgets.  A widget can be marked as needing to be built during
the build phase only if one of its ancestors is currently building. This exception is allowed
because the framework builds parent widgets before children, which means a dirty descendant will
always be built. Otherwise, the framework might not visit this widget during this build phase.
The widget on which setState() or markNeedsBuild() was called was:
_ModalScope<dynamic>-[LabeledGlobalKey<_ModalScopeState<dynamic>>#e51b7]
The widget which was currently being built when the offending call was made was:
LayoutBuilder

以下是导致类错误的

class CustSigninView extends StatefulWidget {
@override
_CustSigninViewState createState() => _CustSigninViewState();
}
class _CustSigninViewState extends State<CustSigninView> {
final TextEditingController _phNoController = TextEditingController();
@override
Widget build(BuildContext context) {
final deviceSize = MediaQuery.of(context).size;
bool tempBool = true;             <------------ TEMP "BOOL" JUST FOR TESTING

return BaseView<CustSignInViewModel>(
builder: (context, model, child) => ResponsiveSafeArea(
builder: (context, widgetSize) => Scaffold(
body: Material(
type: MaterialType.card,
child: Stack(
children: <Widget>[
ListView(  //ListView

// --------  I'M GETTING  E R R O R  IN BELOW LINE.
tempBool
? UIHelper().showErrorButtomSheet(context, "errorText"))
: Container(),
],
),
),
),
),
);
}
}

如果我在tempBool条件下用Container()替换UIHelper().showErrorButtomSheet(context, "errorText"))，它工作得很好。UIHelper().showErrorButtomSheet(context, "errorText"))出现问题。

以下是UIHelper类中的showErrorButtomSheet函数

/// Returns a Error Dialog
Future showErrorButtomSheet(BuildContext context, String errorText) {
Size deviceSize = MediaQuery.of(context).size;
return showModalBottomSheet(
context: context,
builder: (context) => Container(
child: StatefulBuilder(
builder: (BuildContext context, StateSetter stateSetter) {
return Row(
children: <Widget>[
Icon(...),
Text(...),
),
],
);
},
),
),
);
}

ResponsiveSafeArea类看起来像这样。单击Debug Console中的错误包链接后重定向到生成器功能

typedef Responsive_Builder = Widget Function(
BuildContext context,
Size,
);
class ResponsiveSafeArea extends StatelessWidget {
final Responsive_Builder responsiveBuilder;
const ResponsiveSafeArea({
Key key,
@required Responsive_Builder builder,
})  : responsiveBuilder = builder,
super(key: key);
@override
Widget build(BuildContext context) {
return SafeArea(
child: LayoutBuilder(
builder: (context, constraints) {
return responsiveBuilder(
context,
constraints.biggest,
);
},
),
);
}
}

Answer 1

Faizan Kamal您正在尝试显示showModalBottomSheet，它无法像其他小部件一样显示。我建议您使用自定义小部件来显示下面的errorText：

Widget showErrorWidget(BuildContext context, String errorText) {
return Row(
children: <Widget>[
Icon(Icons.error),
Text(errorText),
],
);
}

并像这样使用：

...
tempBool
? UIHelper(). showErrorWidget(context, "errorText"))
: Container(),
...

为了显示对话框，您必须处理一个事件来实现这一点，例如在布局事件之后：

if(!tempBool)
Container(), // We display this container when tempBool is false, else we display the dialog

最后添加afterLayout事件：

@override
void initState() {
WidgetsBinding.instance.addPostFrameCallback((_) => _afterLayout(context));
super.initState();
...
}
_afterLayout(BuildContext context) async {
if(tempBool)
await UIHelper().showErrorButtomSheet(context, "errorText");
}