在小部件初始化中设置提供程序不起作用

Question

我正在尝试在小部件初始化时设置一个提供程序变量，以便小部件具有适当的数据。执行此操作时出现错误。代码如下：

class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
builder: (context) => ListManager(),
child: MaterialApp(
title: 'crud-to-do',
home: Home(), // Home calls ListWidget()
),
);
}
}
class ListWidget extends StatelessWidget {
@override
Widget build(BuildContext context) {
final listManager = Provider.of<ListManager>(context);
listManager.list = [
ListItem(title: 'myTtitle', description: 'My desc', id: '1324j323e')
];
if (listManager.list.isEmpty) return Text("hey");
return Text(listManager.list[0].title);
}
}

这有效，但我收到一个错误：

flutter: ══╡ EXCEPTION CAUGHT BY FOUNDATION LIBRARY ╞════════════════════════════════════════════════════════
flutter: The following assertion was thrown while dispatching notifications for ListManager:
flutter: setState() or markNeedsBuild() called during build.
flutter: This ChangeNotifierProvider<ListManager> widget cannot be marked as needing to build because the
flutter: framework is already in the process of building widgets.  A widget can be marked as needing to be
flutter: built during the build phase only if one of its ancestors is currently building. This exception is
flutter: allowed because the framework builds parent widgets before children, which means a dirty descendant
flutter: will always be built. Otherwise, the framework might not visit this widget during this build phase.
flutter: The widget on which setState() or markNeedsBuild() was called was:
flutter:   ChangeNotifierProvider<ListManager>
flutter: The widget which was currently being built when the offending call was made was:
flutter:   ListWidget
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0      Element.markNeedsBuild.<anonymous closure> 
package:flutter/…/widgets/framework.dart:3680
flutter: #1      Element.markNeedsBuild 
package:flutter/…/widgets/framework.dart:3695
flutter: #2      State.setState

因此，我尝试像这样对listManager.list设置进行initState：

@override
void initState() {
listManager.list = [
ListItem(title: 'myTtitle', description: 'My desc', id: '1324j323e')
];
}

但是我收到一个错误说：

声明"initState"未被引用。

在这两种情况下，我都做错了什么，设置provider的正确方法是什么？

Answer 1

在生成方法中，使用Provider.of<ListManager>(context, listen: false)来防止重新生成。

默认情况下，listen设置为true，并在模型更改时触发重新生成，这将在build()方法或initState()中引发异常。