C＃JSON反序列化：Type是接口或抽象类，无法实例化

Question

I'm using this C# project which uses APIs to communicate with the online trading platform Poloniex .

This code is supposed to get balances in a wallet:

var x = await polo_client.Wallet.GetBalancesAsync();

Although this code gives this error:

Error getting wallet:Could not create an instance of type Jojatekok.PoloniexAPI.WalletTools.IBalance.
Type is an interface or abstract class and cannot be instantiated.
Path '1CR.available', line 1, position 20.

in Helper.cs here:

[SuppressMessage("Microsoft.Usage", "CA2202:Do not dispose objects multiple times")]
internal static T DeserializeObject<T>(this JsonSerializer serializer, string value)
{ 
    using (var stringReader = new StringReader(value))
    {
        using (var jsonTextReader = new JsonTextReader(stringReader))
        {
            return (T)serializer.Deserialize(jsonTextReader, typeof(T));
        }
    } 
}

The code to call this is:

public T GetData<T>(string command, params object[] parameters)
{
    var relativeUrl = CreateRelativeUrl(command, parameters);
    var jsonString = QueryString(relativeUrl);
    var output = JsonSerializer.DeserializeObject<T>(jsonString);
    return output;
}

Can someone tell me why I'm getting an error deserializing this JSON response?

The response is JSON, here is a sample of it:

{
"1CR":{"available":"0.00000000","onOrders":"0.00000000","btcValue":"0.00000000"},
"ABY":{"available":"0.00000000","onOrders":"0.00000000","btcValue":"0.00000000"}
}

Answer 1

JSON or not, the error is self-describing. You can not instantiate an interface or abstract class. They are just blue-prints of what functionality or object structure they'd represent.

For example, you can not do this:

var something = new ISomething();

but, you can do this:

ISomething something = new Something();

All you need is just some concrete implementation of that interface. Something like:

public JsonReceived : IBalance
{
// rest of the implementation
}

Or that might already be provided by the third-party, check their SDK documentation.

Answer 2

This is what i have done to get it working. Thanks to Chris from Guru.com for getting this working. Great guy and very well priced. You can find him here: http://www.guru.com/freelancers/deatc

private IDictionary<string, IBalance> GetBalances()
{
    var postData = new Dictionary<string, object>();
    var data = PostData<IDictionary<string, Balance>>("returnCompleteBalances", postData);
    var returnData = new Dictionary<string, IBalance>();

    foreach (string key in data.Keys)
    {
        returnData.Add(key, data[key]);
    }

    return returnData;
}

Answer 3

The error causing due to DeSerialization of an object, that internally creates an Jobject and Cast it as a input Generic, in the above scenario since we cannot create an object of Interface it is throwing an error, we can achieve in the below ways according to your solution that is posted in GitHub

add a Hashtable as a generic input to PostData method

change your wallet.cs as ex:

 IBalance CreateFactory(string typeOfBalance, string jsonString) { IBalance balance = null; switch (typeOfBalance) { case "balanceClassIdentification": balance = new Balance(); balance = Newtonsoft.Json.JsonConvert.DeserializeObject<Balance>(jsonString); break; case "": // write logic if Ibalance interface implemented in any childClass ex: class stockBalance: IBalance , then balance = new StockBalance();balance = Newtonsoft.Json.JsonConvert.DeserializeObject<stockBalance>(jsonString); default: balance = new Balance(); balance = Newtonsoft.Json.JsonConvert.DeserializeObject<Balance>(jsonString); break; } return balance; } private IDictionary<string, IBalance> GetBalances() { IDictionary<string, IBalance> data = null; var postData = new Dictionary<string, object>(); //var data = PostData<IDictionary<string, object>>("returnCompleteBalances", postData); Hashtable output = PostData<Hashtable>("returnCompleteBalances", postData); if (output.Count > 0) { data = new Dictionary<string, IBalance>(); } foreach (string jsonObjKey in output.Keys) { IBalance balace = CreateFactoty("balanceClassIdentification", output[jsonObjKey].ToString()); // this "balanceClassIdentification" just used as a string but we can add the condition in createFactory according to the type of object that wallet data.Add(jsonObjKey, balace); } return data; } 

Create another intermediate class that implemented Ibalance

like

 public class BalanceBase: IBalace { } 

need to change the balance class

 private IDictionary<string, Balance> GetBalances()
        {

            var postData = new Dictionary<string, object>();
            var data = PostData<IDictionary<string, Balance>>("returnCompleteBalances", postData);

            return data;
        }

if No other classes are implemented for IBalance except balance

you can directly use return type for GetBalance() method as IDictionary and change the implementaion

  private IDictionary<string, Balance> GetBalances() { var postData = new Dictionary<string, object>(); var data = PostData<IDictionary<string, Balance>>("returnCompleteBalances", postData); return data; }