尝试在MVC中使用Web Api数据时的空对象引用

Question

从我之前的帖子开始，我正在为一个大学项目制作一个网络ATM。为此，我有一个MVC应用程序，其中大部分功能都是基于它，以及一个API项目，其中包含一个数据库。我正在尝试使用此数据库中的数据并将其显示在我的索引方法中。但是，当我运行我的解决方案时，我在索引视图的以下行给出了一个空对象引用：

  @foreach (var item in Model.ExcRateList)

我正在努力弄清楚为什么这不起作用，并且正在向你们寻求可能的解决方案。

以下是我的控制器中的索引获取方法：

   // GET: AtmAccounts
    public ActionResult Index()
    {
        ViewModels.ExcClient ex = new ViewModels.ExcClient();
        ViewBag.listRates = ex.findAll();
        var userID = User.Identity.GetUserId();
        ViewModels.AtmAccountVM atmVm = new ViewModels.AtmAccountVM();
        atmVm.AtmAccountList = db.AtmAccounts.Where(a => a.UserId == userID).ToList();
        atmVm.UserName = User.Identity.GetUserName();
        atmVm.ExcRateList = ViewBag.listRates;
        return View(atmVm);
 }

涉及此问题的部分是：

  ViewModels.ExcClient ex = new ViewModels.ExcClient();
        ViewBag.listRates = ex.findAll();

和

atmVm.ExcRateList = ViewBag.listRates;

视图模型AtmAccountVM控制我的不同方法之间传递的值，包括我的API（或者至少应该）：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using ATMApplication.Models;
using System.Data.SqlClient;

namespace ATMApplication.ViewModels
{
public class AtmAccountVM
{
    public List<AtmAccount> AtmAccountList { get; set; }
    public List<Transaction> TransactionsList { get; set; }
    public string UserName { get; set; }

    public int Id { get; set; }

    //These variables are used for the various ATM functions accessible to     customers
    public decimal DepositAmount { get; set; }
    public decimal WithdrawAmount { get; set; }
    public decimal TransferAmount { get; set; }
    public string AccTransfer { get; set; }


    // These are Used for the Restful Service
    public int id { get; set; }
    public string Code { get; set; }
    public string Name { get; set; }
    public decimal Rate { get; set; }
    public List<ExcRate> ExcRateList { get; set; }





    }
  }    

以下是视图模型ExcRate，它存储从API检索的数据，以及获取它的ExcClient：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;


namespace ATMApplication.ViewModels
{
public class ExcRate
{
    public int id { get; set; }
    public string Code { get; set; }
    public string Name { get; set; }
    public decimal Rate { get; set;}
}
}



using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using Newtonsoft.Json;



namespace ATMApplication.ViewModels
{
public class ExcClient
{
    private string Base_Url = "http://localhost.57341/api/values";

    public IEnumerable<ExcRate> findAll()
    {


        try
        {
            HttpClient client = new HttpClient();
            client.BaseAddress = new Uri(Base_Url);
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            HttpResponseMessage response = client.GetAsync("rates").Result;
            if (response.IsSuccessStatusCode)
            {
                var responseData = response.Content.ReadAsStringAsync().Result;
                var Rates = JsonConvert.DeserializeObject<List<ExcRate>>(responseData);
                return Rates;
            }
            return null;
        }
        catch
        {
            return null;
        }
    }
}
}

最后，这里是索引视图，其底部部分用于在表格中显示此数据：

@using ATMApplication.ViewModels
@model ATMApplication.ViewModels.AtmAccountVM


<h2> Accounts Held for Customer: @Model.UserName </h2>

<p>
@Html.ActionLink("Create New Account", "Create")
</p>
<style typw ="text/css">
span {
color: darkcyan;

}

</style>
<div style="background-color:lightyellow; color: black;">


<table class="table">

    <tr>
        <th>
            @Html.DisplayNameFor(model => model.AtmAccountList.First().AccountNumber)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.AtmAccountList.First().AccountBalance)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.AtmAccountList.First().AccType.AccountType)
        </th>
        <th></th>
    </tr>

    @foreach (var item in Model.AtmAccountList)
    {

        <tr>

            <td>
                <div style="background-color:lightyellow">
                    @Html.DisplayFor(modelItem => item.AccountNumber)
                </div>
            </td>
            <td>
                <div style="background-color:lightyellow">
                    @Html.DisplayFor(modelItem => item.AccountBalance)
                </div>
            </td>
            <td>
                <div style="background-color:lightyellow">
                    @Html.DisplayFor(modelItem => item.AccType.AccountType)
                </div>
            </td>
            <td>
                <div style="background-color:lightyellow">
                    @Html.ActionLink("Deposit", "Deposit", new { id = item.Id })
                </div>
                <div style="background-color:lightyellow">
                    @Html.ActionLink("Quick Withdraw", "Quick Withdraw", new { id = item.Id })
                </div>
                <div style="background-color: lightyellow">
                    @Html.ActionLink("Withdraw", "Withdraw", new { id = item.Id })
                </div>
                <div style="background-color:lightyellow">
                    @Html.ActionLink("Transfer", "Transfer", new { id = item.Id })
                </div>
                <div style="background-color:lightyellow">
                    @Html.ActionLink("Transactions", "Transactions", new { id = item.Id })
                    <input type="hidden" name="Id" value="@Model.AtmAccountList[0].Id" />
                </div>

            </td>
        </tr>

    }
</table>
</div>

<br />
<br />
<h2>Exchange Rates</h2>
<p>
These are the current exchange rates (in GBP):
</p>
<br/>
<div style="background-color:lightcyan">
<table class="table">
   <tr>

       <th>Currency Code</th>
       <th>Currency Name</th>
       <th>Exchange Rate (GBP)</th>
   </tr>
   @foreach (var item in Model.ExcRateList)
   {
       <tr>
           <td>@item.Code</td>
           <td>@item.Name</td>
           <td>@item.Rate</td>
       </tr>
   }
</table>
</div>