android - 调用api时如何处理map<dynamic> null对象

Question

如果 status 不是 200，我如何管理服务器响应。

@JsonSerializable(nullable: false)
class LoginResponse {
  final String error;
  final int status;
  final List<User> userList;
  LoginResponse({this.error, this.status, this.userList});

  factory LoginResponse.fromJson(Map repJson){

List<dynamic> userListResp=repJson['userData'];
List<User> userList=userListResp.map((e)=>User.fromUser(e)).toList();
int s=repJson['status'];
   if(s==200){
     return LoginResponse(error:repJson['error'],status: repJson['status'],userList:userList);
   } else{
     return LoginResponse(error:repJson['error'],status: repJson['status']);
   }}}

  class User{
  String cust_id;
  String cust_name;
  String cust_email;
  String cust_mob;

  User({this.cust_id,this.cust_name,this.cust_email,this.cust_mob});
  factory User.fromUser(Map userJson){
    return User(cust_id: userJson['cust_id'],cust_name: userJson['cust_name'],
        cust_email: userJson['cust_email'],cust_mob: userJson['cust_mob']);
  }
}

发生错误时的服务器响应

{"error":"1","status":201,"message":"Entered email id already exist in our records"}

成功时服务器响应

  {
"error":"0",
"status":200,
"userData":[
 {
    "cust_id":"87",
    "cust_name":"kio",
    "cust_email":"kio1@kio.com",
    "cust_gend":null,
    "cust_dob":null,
    "cust_mob":"098998899889588",
    "cust_pass":"e10adc3949ba59abbe56e057f20f883e",
    "cust_age":null,
    "device_type":"android",
    "device_token":"eNWqzDwxqsQ:APA91bF-uK1MI11D3SgHGSw7Omv1imjDrPKBBCrN9JgmyJppHsNVeG5l56EkCCd5ZMaxL_ehQzVhtoEj0fTNB55wYGJt5BqYVvwfAb7HrBqwb_21M6VFPuF6LQINkvE1offQgZYweROO",
    "status":"0",
    "createAt":"2019-01-31 18:45:19",
    "updatedAt":"0000-00-00 00:00:00",
    "login_type":"",
    "login_id":null,
    "is_guest":"0",
    "auth_token":"",
    "forgot_token":null
 }]
}

当用户数据不存在或为空时如何管理，我尝试在状态代码为 201 但仍然显示时进行管理

NoSuchMethodError: The method 'map' was called on null.

Answer 1

要修复您的代码，请将 userList 映射移动到 if block 中。这样你将解析只有状态码为 200 的响应。

int s=repJson['status'];
if (s==200) {
  List<dynamic> userListResp=repJson['userData'];
  List<User> userList=userListResp.map((e)=>User.fromUser(e)).toList();
  return LoginResponse(error:repJson['error'], status:repJson['status'], userList:userList);
} else {
  return LoginResponse(error:repJson['error'], status:repJson['status']);
}

但是，您可能不想处理模型中的错误。最好在执行请求后检查错误，然后再决定是否要解析响应。

像这样的东西会更容易处理并且不会污染你的模型对象:

final response = await client.get(requestUrl);
if (response.statusCode == 200) {
  // If the call to the server was successful, parse the JSON
  final loginResponse = LoginResponse.fromJson(json.decode(response.body));

  // ...
} else {
  // If that call was not successful, throw an error or parse the error object.
  throw Exception('Failed to login');

  // ...
}