然后在未来中返回未来

Question

我有两个共同的偏好

<string name="flutter.39281a04d2b8c8ba">{"name":"student","id":"UmWq","token":"LVF-M","isIncoming":true,"uuid":"39281a04d2b8c8ba"}</string>

<string name="flutter.4c434612edcff4bc">{"name":"student","id":"ozjU","token":"GXUTR","isIncoming":true,"uuid":"4c434612edcff4bc"}</string>

我有一个id，我想从这个id中检索uuid，以便创建一个文件：

MySharedPreferences.getUuid(id).then((uuid) {
   print("ended up with this uuid: $uuid");
   FileManager.createFile(uuid, form.title).then((file) => {
       file.writeAsString(str)
   });
});

这是getUuid方法：

static Future<String> getUuid(String id) async {
    final prefs = await SharedPreferences.getInstance();
    for (String key in prefs.getKeys()){
      print("looking at $key");
      if (!key.contains("#")){
        return getData(key).then((value){
          print("got this value: $value");
          Map<String, dynamic> endpointJson = jsonDecode(value);
          EndpointData endpoint = EndpointData.fromJson(endpointJson);
          print("endpoint.id: ${endpoint.id}");
          print("id: $id");
          if (endpoint.id == id){
            print("the good return");
            return endpoint.uuid;
          }
          return null;
        });
      }else{
        continue;
      }
    }
  }

如您所见，getUuid检索共享首选项中的所有键的列表，并对它们进行迭代。对于每个键，我读取相关的数据并检查id是否与我的匹配，因此返回uuid。

现在，我知道问题所在，但我找不到解决它的方法。问题如下。假设我的id是ozjU，我的getUuid函数会按顺序迭代键，所以如果第一次检查39281a04d2b8c8ba。39281a04d2b8c8ba的id不等于我的id，所以在getData内部返回null，这使得getUuid也返回null。我不知道如何让getData在endpoint.id == id或不返回任何东西的情况下返回值，并让外部的for继续迭代其余的键。

EDIT:根据要求，测试如下，但uuid仍然为空：

static Future<String> getUuid(String id) async {
    final prefs = await SharedPreferences.getInstance();
    for (String key in prefs.getKeys()){
      print("looking at $key");
      if (!key.contains("#")){
        return getData(key).then((value){
          print("got this value: $value");
          Map<String, dynamic> endpointJson = jsonDecode(value);
          EndpointData endpoint = EndpointData.fromJson(endpointJson);
          print("endpoint.id: ${endpoint.id}");
          print("id: $id");
          if (endpoint.id == id){
            print("the good return");
            return endpoint.uuid;
          }
        });
      }else{
        continue;
      }
    }
    return null;
  }

最终编辑:等待getData结果如下：

static Future<String> getUuid(String id) async {
    final prefs = await SharedPreferences.getInstance();
    for (String key in prefs.getKeys()){
      print("looking at $key");
      if (!key.contains("#")){
        var value = await getData(key);
        print("got this value: $value");
        Map<String, dynamic> endpointJson = jsonDecode(value);
        EndpointData endpoint = EndpointData.fromJson(endpointJson);
        print("endpoint.id: ${endpoint.id}");
        print("id: $id");
        if (endpoint.id == id){
          print("the good return");
          return endpoint.uuid;
        }
      }else{
        continue;
      }
    }
    return null;
  }

Answer 1

正确的代码：

static Future<String> getUuid(String id) async {
    final prefs = await SharedPreferences.getInstance();
    for (String key in prefs.getKeys()){
      print("looking at $key");
      if (!key.contains("#")){
        var value = await getData(key);
        print("got this value: $value");
        Map<String, dynamic> endpointJson = jsonDecode(value);
        EndpointData endpoint = EndpointData.fromJson(endpointJson);
        print("endpoint.id: ${endpoint.id}");
        print("id: $id");
        if (endpoint.id == id){
          print("the good return");
          return endpoint.uuid;
        }
      }else{
        continue;
      }
    }
    return null;
  }