先貼一下該方法的源碼：

/*** Handles errors emitted by this [Future].** This is the asynchronous equivalent of a "catch" block.** Returns a new [Future] that will be completed with either the result of* this future or the result of calling the `onError` callback.** If this future completes with a value,* the returned future completes with the same value.** If this future completes with an error,* then [test] is first called with the error value.** If `test` returns false, the exception is not handled by this `catchError`,* and the returned future completes with the same error and stack trace* as this future.** If `test` returns `true`,* [onError] is called with the error and possibly stack trace,* and the returned future is completed with the result of this call* in exactly the same way as for [then]'s `onError`.** If `test` is omitted, it defaults to a function that always returns true.* The `test` function should not throw, but if it does, it is handled as* if the `onError` function had thrown.** Note that futures don't delay reporting of errors until listeners are* added. If the first `catchError` (or `then`) call happens after this future* has completed with an error then the error is reported as unhandled error.* See the description on [Future].*/// The `Function` below stands for one of two types:// - (dynamic) -> FutureOr<T>// - (dynamic, StackTrace) -> FutureOr<T>// Given that there is a `test` function that is usually used to do an// `isCheck` we should also expect functions that take a specific argument.// Note: making `catchError` return a `Future<T>` in non-strong mode could be// a breaking change.Future<T> catchError(Function onError, {bool test(Object error)}); 復制代碼

翻譯一下主要的意思，就是這個catchError方法可以捕獲其他Futrue的異常信息，如果重寫了test方法，test返回true就可以在catchError的onError方法里捕獲到異常，如果test返回false，就把該異常繼續拋出而不會在catchError方法里被捕獲，如果不寫test默認實現一個返回true的test方法，注意catchError只能捕獲Future的異常，而不能捕獲同步代碼的異常，測試代碼如下：

import 'dart:async';Future testFutureError() {return new Future(() {throw "error";//1 // return "abc";//2}); }main() {testFutureError().then((value) {print("then " + value);}).catchError((e) {print("catchError " + e);}, test: (Object o) {print("test " + o);return true;//3 // return false;//4}).catchError((e) {print("catchError2 " + e);}, test: (_) => true); } 復制代碼

如果是上面的代碼，會輸出

test error catchError error 復制代碼

因為//3這行返回了true，所以會在第一個catchError里被捕獲。 如果//4不注釋了，把//3注釋，那么第一個catchError不能捕獲該異常，該異常會繼續拋出，然后在第二個catchError里被捕獲。具體的可自行測試。

還有就是用whenComplete方法的時候，不是所有then都執行完再執行whenComplete方法，而是then、catchError、whenComplete這些方法會按照順序（除非中途有異常會進入下一個catchError）執行，這一點和rxjava+retrofit不一樣，原生開發請知悉。

總結

以上是生活随笔為你收集整理的Dart中的catchError捕获顺序的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。