Alfred框架异步处理函数执行顺序错乱，如何实现预期执行逻辑？

问题原因 #

Dart 中的 Timer.periodic 属于非阻塞异步 API，调用后会立即返回，不会等待定时器回调内的异步逻辑执行完成。虽然你给 complexTendexAPIRequest 加了 async 修饰，但函数在创建完定时器后就直接结束返回了，外层的 await complexTendexAPIRequest(...) 并没有真正等待轮询、拉取结果、写文件的完整流程执行完成，因此会出现输出顺序错乱的问题。

修复方案 #

方案1：用 Completer 封装 Timer 逻辑（保留 Timer 实现） #

可以通过 Completer 包装整个轮询流程，只有当所有操作执行完成后再标记流程结束，外层的 await 就能正常等待整个函数执行完成：

import 'dart:async';

// 明确声明返回 Future<void>
Future<void> complexTendexAPIRequest(Map<String, dynamic> data) async {
  print('Request: $data');
  final completer = Completer<void>();
  try {
      final response = await http.post(
        Uri.parse(COMPLEX_URL),
        headers: {'Content-Type': 'application/json', 'Authorization': 'bearer $ACCESS_TOKEN'},
        body: json.encode(data)
      );

      if(response.statusCode == 200) {
        var res = json.decode(response.body);
        int latestId = res['id'];
        String url = 'https://api.ru/v2/complex/status?id=$latestId';
        stdout.write('Waiting for "complete" status from API: ');
        Timer.periodic(Duration(seconds: 1), (timer) async {
          try {
            final response = await http.get(
              Uri.parse(url),
              headers: {'Content-Type': 'application/json', 'Authorization': 'bearer $ACCESS_TOKEN'}
            );

            var data = json.decode(response.body);
            if(data['status'] == 'completed') {
              timer.cancel();
              stdout.write('[DONE]');
              stdout.write('\nFetching result: ');
              String url = "https://api.ru/v2/complex/results?id=$latestId";
              final response = await http.get(
                Uri.parse(url),
                headers: {'Content-Type': 'application/json', 'Authorization': 'bearer $ACCESS_TOKEN'}
              );
              stdout.write('[DONE]');
              var data = prettyJson(json.decode(response.body));
              await File('result.json').writeAsString(data.toString());
              print("\nCreating dump of result: [DONE]");
              // 所有逻辑执行完成，标记结束
              completer.complete();
            }
          } catch(e) {
            timer.cancel();
            // 轮询过程出现异常，向外抛出
            completer.completeError(e);
          }
        });
        
      }
      else {
        print('[ERROR] Wrong status code for complex request. StatusCode: ${response.statusCode}');
        completer.complete();
      }
  } 
  on SocketException catch(e) {
    print('No Internet connection: $e');
    completer.completeError(e);
  } on TimeoutException catch(e) {
    print('TenderAPI Timeout: $e');
    completer.completeError(e);
  } on Exception catch(e) {
    print('Some unknown Exception: $e');
    completer.completeError(e);
  }
  // 返回 Completer 的 Future 供外层 await
  return completer.future;
}

方案2：改用 while 循环实现轮询（更简洁的方案） #

这种方案不需要额外引入 Completer，本身就是顺序执行的异步逻辑，外层 await 可以直接等待整个流程结束，也是你当前已经验证可行的方案：

Future<void> complexTendexAPIRequest(Map<String, dynamic> data) async {
  print('Request: $data');
  try {
      final response = await http.post(
        Uri.parse(COMPLEX_URL),
        headers: {'Content-Type': 'application/json', 'Authorization': 'bearer $ACCESS_TOKEN'},
        body: json.encode(data)
      );

      if(response.statusCode == 200) {
        var res = json.decode(response.body);
        int latestId = res['id'];
        String statusUrl = 'https://api.ru/v2/complex/status?id=$latestId';
        stdout.write('Waiting for "complete" status from API: ');
        // while 循环轮询状态
        while(true) {
          final response = await http.get(
            Uri.parse(statusUrl),
            headers: {'Content-Type': 'application/json', 'Authorization': 'bearer $ACCESS_TOKEN'}
          );
          var statusData = json.decode(response.body);
          if(statusData['status'] == 'completed') {
            break;
          }
          // 每秒轮询一次
          await Future.delayed(Duration(seconds: 1));
        }
        stdout.write('[DONE]');
        stdout.write('\nFetching result: ');
        String resultUrl = "https://api.ru/v2/complex/results?id=$latestId";
        final resultResponse = await http.get(
          Uri.parse(resultUrl),
          headers: {'Content-Type': 'application/json', 'Authorization': 'bearer $ACCESS_TOKEN'}
        );
        stdout.write('[DONE]');
        var resultData = prettyJson(json.decode(resultResponse.body));
        await File('result.json').writeAsString(resultData.toString());
        print("\nCreating dump of result: [DONE]");
      }
      else {
        print('[ERROR] Wrong status code for complex request. StatusCode: ${response.statusCode}');
      }
  } 
  on SocketException catch(e) {
    print('No Internet connection: $e');
    rethrow;
  } on TimeoutException catch(e) {
    print('TenderAPI Timeout: $e');
    rethrow;
  } on Exception catch(e) {
    print('Some unknown Exception: $e');
    rethrow;
  }
}

以上两种方案都可以保证 print('Hello World') 和 await res.json({'data': 'ok'}) 会在 complexTendexAPIRequest 所有逻辑执行完成后再运行。

内容的提问来源于stack exchange，提问作者Dmitry Bubnenkov