# 在 Flutter 里处理错误 > 如何在 Flutter 里处理和打印错误信息 The Flutter framework catches errors that occur during callbacks triggered by the framework itself, including errors encountered during the build, layout, and paint phases. Errors that don't occur within Flutter's callbacks can't be caught by the framework, but you can handle them by setting up an error handler on the [`PlatformDispatcher`][]. Flutter 框架会捕获框架自身触发的回调期间发生的错误，包括构建、布局和绘制阶段遇到的错误。 不在 Flutter 回调内发生的错误无法被框架捕获，但你可以通过在 [`PlatformDispatcher`][] 上设置错误处理器来处理它们。 All errors caught by Flutter are routed to the [`FlutterError.onError`][] handler. By default, this calls [`FlutterError.presentError`][], which dumps the error to the device logs. When running from an IDE, the inspector overrides this behavior so that errors can also be routed to the IDE's console, allowing you to inspect the objects mentioned in the message. 所有 Flutter 的错误均会被回调方法 [`FlutterError.onError`][] 捕获。 默认情况下，会调用 [`FlutterError.presentError`][] 方法， 并将错误转储到当前的设备日志中。 当从 IDE 运行应用时，检查器重写了该方法， 错误也被发送到 IDE 的控制台，可以在控制台中检查出错的对象。 :::note Consider calling [`FlutterError.presentError`][] from your custom error handler in order to see the logs in the console as well. 考虑从自定义错误处理程序调用 [`FlutterError.presentError`][] 以查看控制台中的日志。 ::: When an error occurs during the build phase, the [`ErrorWidget.builder`][] callback is invoked to build the widget that is used instead of the one that failed. By default, in debug mode this shows an error message in red, and in release mode this shows a gray background. 当构建期间发生错误时，回调函数 [`ErrorWidget.builder`][] 会被调用， 来生成一个新的 widget，用来代替构建失败的 widget。 默认情况，debug 模式下会显示一个红色背景的错误页面， release 模式下会展示一个灰色背景的空白页面。 When errors occur without a Flutter callback on the call stack, they are handled by the `PlatformDispatcher`'s error callback. By default, this only prints errors and does nothing else. 如果错误发生时调用堆栈上没有 Flutter 回调， 它们会由 `PlatformDispatcher` 的错误回调处理。 默认情况下，它仅会打印错误，而不执行其他任何操作。 You can customize these behaviors, typically by setting them to values in your `void main()` function. 这些回调方法都可以被重写，通常在 `void main()` 方法中重写。 Below each error type handling is explained. At the bottom there's a code snippet which handles all types of errors. Even though you can just copy-paste the snippet, we recommend you to first get acquainted with each of the error types. 下面解释了所有的错误捕获类型。 在最后的代码段可以用于处理所有类型的错误。 尽管你可以直接复制粘贴代码段，但我们建议你先了解每种错误类型。 ## Errors caught by Flutter ## 被 Flutter 捕获的错误 For example, to make your application quit immediately any time an error is caught by Flutter in release mode, you could use the following handler: 例如，如果你想在 release 模式下发生错误时立刻关闭应用， 可以使用下面的回调方法: ```dart import 'dart:io'; import 'package:flutter/foundation.dart'; import 'package:flutter/material.dart'; void main() { FlutterError.onError = (details) { FlutterError.presentError(details); if (kReleaseMode) exit(1); }; runApp(const MyApp()); } // The rest of the `flutter create` code... ``` :::note The top-level [`kReleaseMode`][] constant indicates whether the app was compiled in release mode. 顶层的 [`kReleaseMode`][] 常数表示该应用是否在 release 模式下编译。 ::: This handler can also be used to report errors to a logging service. For more details, see our cookbook chapter for [reporting errors to a service][]. 这个回调方法也可以上报错误到日志服务平台。更多信息可以查看文档 [报错信息通过服务上传][reporting errors to a service]。 ## Define a custom error widget for build phase errors ## 自定义一个 ErrorWidget 以展示 build 时的错误 To define a customized error widget that displays whenever the builder fails to build a widget, use [`MaterialApp.builder`][]. 定义一个自定义的 error widget，以当 builder 构建 widget 失败时显示， 请使用 [`MaterialApp.builder`][]。 ```dart class MyApp extends StatelessWidget { const MyApp({super.key}); @override Widget build(BuildContext context) { return MaterialApp( builder: (context, widget) { Widget error = const Text('...rendering error...'); if (widget is Scaffold || widget is Navigator) { error = Scaffold(body: Center(child: error)); } ErrorWidget.builder = (errorDetails) => error; if (widget != null) return widget; throw StateError('widget is null'); }, ); } } ``` ## Errors not caught by Flutter ## 未被 Flutter 捕获的错误 Consider an `onPressed` callback that invokes an asynchronous function, such as `MethodChannel.invokeMethod` (or pretty much any plugin). For example: 假设一个 `onPressed` 回调调用了异步方法，例如 `MethodChannel.invokeMethod` （或者其他 plugin 的方法）： ```dart OutlinedButton( child: const Text('Click me!'), onPressed: () async { const channel = MethodChannel('crashy-custom-channel'); await channel.invokeMethod('blah'); }, ) ``` If `invokeMethod` throws an error, it won't be forwarded to `FlutterError.onError`. Instead, it's forwarded to the `PlatformDispatcher`. 如果 `invokeMethod` 抛出了错误，它不会传递至 `FlutterError.onError`， 而是转发给 `PlatformDispatcher`。 To catch such an error, use [`PlatformDispatcher.instance.onError`][]. 如果你想捕获这样的错误，请使用 [`PlatformDispatcher.instance.onError`][]。 ```dart import 'package:flutter/material.dart'; import 'dart:ui'; void main() { MyBackend myBackend = MyBackend(); PlatformDispatcher.instance.onError = (error, stack) { myBackend.sendError(error, stack); return true; }; runApp(const MyApp()); } ``` ## Handling all types of errors ## 处理所有类型的错误 Say you want to exit application on any exception and to display a custom error widget whenever a widget building fails - you can base your errors handling on next code snippet: 如果你想在异常抛出时退出应用，并在 build 错误时展示自定义的 ErrorWidget， 你可以在下面的代码片段的基础上定制你的处理： ```dart import 'package:flutter/material.dart'; import 'dart:ui'; Future main() async { await myErrorsHandler.initialize(); FlutterError.onError = (details) { FlutterError.presentError(details); myErrorsHandler.onErrorDetails(details); }; PlatformDispatcher.instance.onError = (error, stack) { myErrorsHandler.onError(error, stack); return true; }; runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); @override Widget build(BuildContext context) { return MaterialApp( builder: (context, widget) { Widget error = const Text('...rendering error...'); if (widget is Scaffold || widget is Navigator) { error = Scaffold(body: Center(child: error)); } ErrorWidget.builder = (errorDetails) => error; if (widget != null) return widget; throw StateError('widget is null'); }, ); } } ``` [`ErrorWidget.builder`]: https://api.flutter-io.cn/flutter/widgets/ErrorWidget/builder.html [`FlutterError.onError`]: https://api.flutter-io.cn/flutter/foundation/FlutterError/onError.html [`FlutterError.presentError`]: https://api.flutter-io.cn/flutter/foundation/FlutterError/presentError.html [`kReleaseMode`]: https://api.flutter-io.cn/flutter/foundation/kReleaseMode-constant.html [`MaterialApp.builder`]: https://api.flutter-io.cn/flutter/material/MaterialApp/builder.html [reporting errors to a service]: /cookbook/maintenance/error-reporting [`PlatformDispatcher.instance.onError`]: https://api.flutter-io.cn/flutter/dart-ui/PlatformDispatcher/onError.html [`PlatformDispatcher`]: https://api.flutter-io.cn/flutter/dart-ui/PlatformDispatcher-class.html