如何使用C / C ++编写的函数从dart进行异步调用？

Question

I carefully read the article https://www.dartlang.org/articles/server/native-extensions and first decided to just test the standard example that is in the sdk-master/samples/sample_extension folder. The synchronous call works, but when executing the $ dart test_sample_asynchronous_extension.dart command, an "Unhandled exception" error occurs:

~/Downloads/sdk-master/samples/sample_extension $ dart test_sample_asynchronous_extension.dart
Unhandled exception:
type 'Future<dynamic>' is not a subtype of type 'Future<List<int>>'
#0      RandomArray.randomArray (file:///home/michael_k/Downloads/sdk-master/samples/sample_extension/sample_asynchronous_extension.dart:32:5)
#1      main (file:///home/michael_k/Downloads/sdk-master/samples/sample_extension/test_sample_asynchronous_extension.dart:17:5)
#2      _startIsolate.<anonymous closure> (dart:isolate/runtime/libisolate_patch.dart:289:19)
#3      _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
~/Downloads/sdk-master/samples/sample_extension $

Can anyone know how to solve the problem?

Answer 1

I can see the sample files for the example has recently been updated. Try use the latest version of this file: https://github.com/dart-lang/sdk/blob/master/samples/sample_extension/sample_asynchronous_extension.dart

The recent change is the following which seems to fix your problem:

Before:

    var completer = new Completer();

After:

    var completer = new Completer<List<int>>();