c# - 使用Newtonsoft和biding View(MVVM)反序列化JSON

Question

我是C#和Xamarin的初学者。我正在尝试使用newtonsoft反序列化json数组吗？
这是我的json文件:

{
    "next": {
        "$ref": "http://192.168.0.100:8080/ords/hr/employees/?page=1"
    },
    "items": [
        {
            "empno": 7369,
            "ename": "SMITH",
            "job": "CLERK",
            "mgr": 7902,
            "sal": 800,
            "deptno": 20
        },
        {
            "empno": 7934,
            "ename": "MILLER",
            "job": "CLERK",
            "mgr": 7782,
            "sal": 1300,
            "deptno": 10
        }
    ]
}

她是我的模特类:

public class RootObject
    {
        [JsonProperty("items")]
        public Item[] Items { get; set; }

        [JsonProperty("next")]
        public Next Next { get; set; }
    }

    public class Next
    {
        [JsonProperty("$ref")]
        public string Ref { get; set; }
    }

    public class Item
    {
        [JsonProperty("deptno")]
        public long Deptno { get; set; }

        [JsonProperty("empno")]
        public long Empno { get; set; }

        [JsonProperty("ename")]
        public string Ename { get; set; }

        [JsonProperty("job")]
        public string Job { get; set; }

        [JsonProperty("mgr")]
        public long Mgr { get; set; }

        [JsonProperty("sal")]
        public long Sal { get; set; }
    }

当我尝试反序列化为List时，它将在此行上引发异常:

var data = JsonConvert.DeserializeObject<List<RootObject>>(json);

错误是:

Additional information: Cannot deserialize the current JSON object (e.g. {"name":"value"}) into type 'System.Collections.Generic.List`1[System.Object]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly.

To fix this error either change the JSON to a JSON array (e.g. [1,2,3]) or change the deserialized type so that it is a normal .NET type (e.g. not a primitive type like integer, not a collection type like an array or List) that can be deserialized from a JSON object. JsonObjectAttribute can also be added to the type to force it to deserialize from a JSON object.

这段代码对Json进行了反序列化，但是我现在不检索数据并填充类:

public class ApiServices    {


        public async Task<RootObject> GetRootObject()
        {
            var client = new HttpClient();
            var url = string.Format("http://mysite/ords/hr/employees");
            var response = await client.GetAsync(url);

            var json = await response.Content.ReadAsStringAsync();

           dynamic jsonDe = JsonConvert.DeserializeObject<RootObject>(json);

            return jsonDe;
        }

我已经在MainViewModel中创建了一些代码，但是我不知道如何检索数据并插入类Item:

public class MainViewModel
    {
        #region Properties
     
        public ObservableCollection<RootItemViewModel> RootObjects { get; set; }

        private ApiServices apiServices;

        #endregion

        #region Constructors
        public MainViewModel()
        {
            //Create observable collections
            RootObjects = new ObservableCollection<RootItemViewModel>();

            //Instance services
            apiServices = new ApiServices();

            //Load Data
            LoadData();
        }
        #endregion

        #region Methods


        private async void LoadData()

        {
            var emps = new RootObject();
                      
            emps = await apiServices.GetRootObject();

            RootObjects.Clear();

            foreach (var item in RootObjects)
            {

                RootObjects.Add(new RootItemViewModel
                {


                });
            }
        }
            
        #endregion
    }
}

RootItemViewModel类:

    public class RootItemViewModel : RootObject
    {

       
    }

Answer 1

1)您的Json响应显示，它仅包含RootObject类型的实例。

2) var data = JsonConvert.DeserializeObject<List<RootObject>>(json); 将不起作用，因为您尝试将RootObject转换为List<RootObject>。在您的错误响应中进行了描述。

3) dynamic jsonDe = JsonConvert.DeserializeObject<RootObject>(json);将起作用，因为在这里您将RootObject转换为RootObject。我还建议您使用“var”代替“dynamic”(请查看原因:dynamic vs var)

4)您的以下方法似乎存在错误:

private async void LoadData()
{
    var emps = new RootObject();

    emps = await apiServices.GetRootObject();

    RootObjects.Clear();

    //Mistake:
    //You iterate through the previously cleared observable collection.
    //it really should be "foreach (var item in emps.Items)"
    foreach (var item in RootObjects)
    {

        RootObjects.Add(new RootItemViewModel
        {


        });
    }
}

5)您似乎想用 Item上的 RootObject类型的数组喂可观察的集合:

public class RootObject
    {
        [JsonProperty("items")]
        public Item[] Items { get; set; } //This property

        [JsonProperty("next")]
        public Next Next { get; set; }
    }

因此，您实际上应该做的是像这样设置数据:

private async void GetRootObjectItems()
        {
            RootObject emps = await apiServices.GetRootObject();   //Get the root object
            RootObjects.Clear();                        //clear the list

            foreach (var item in emps.Items)    //Important, to get the data from the Array on the RootObject
            {
                ///its a nice way to give your viewmodel a ctor signature that ensures a correct initialization
                ///public RootItemViewModel(Item item)
                ///{ 
                /// this.Deptno = item.Deptno;
                ///}
                RootObjects.Add(new RootItemViewModel(item));  
            }
        }
    }

6)从 RootItemViewModel继承 RootObject没有任何意义。您应该使它继承自 Item或使其拥有 Item类型的属性。

希望我能把事情弄清楚!