接收錯誤消息：System.Reflection.TargetException：非靜態方法需要目標

Question

我正在使用Visual Studio 2013 Update 2，並且在我的一個控制器中出現未處理的異常，我無法確定它的位置來自（哪裏。 這是控制器：

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Net; 
using System.Threading.Tasks; 
using System.Web; 
using System.Web.Mvc; 
using System.Data.Entity; 
using Microsoft.AspNet.Identity; 

namespace SophicCeramics.Controllers 
{ 
public class ShopController : BaseController 
{ 
public ActionResult Cart() 
    { 
     var order = FindOrCreateOrder(); 
     var m = new Models.Order.Cart(); // 
     m.Date = order.OrderDate; 
     m.Total = order.OrderLineItems.Sum(i => i.Quantity * i.UnitPrice); 
     m.ItemCount = order.OrderLineItems.Count; 
     m.Items = order.OrderLineItems.ToList(); 
     return View(m); 
    } 
    public async Task<ActionResult> AddItem(int productId) 
    { 
     var product = _context.Products.FirstOrDefault(p => p.ProductId == productId); 
     var order = FindOrCreateOrder(); 
     var item = order.OrderLineItems.FirstOrDefault(i => i.ProductId == productId); 
     if (item != null) 
     { 
      item.Quantity++; 
      await _context.SaveChangesAsync(); 
     } 
     else 
     { 
      item = new OrderLineItem(); 
      item.OrderHeader = order; 
      item.Product = product; 
      item.Quantity = 1; 
      item.UnitPrice = product.Price; 
      order.OrderLineItems.Add(item); 
      await _context.SaveChangesAsync(); 
     } 
     return RedirectToAction("Cart"); 
    } 
    private OrderHeader FindOrCreateOrder() 
    { 
     var UserName = this.User.Identity.Name; 
     var user = UserManager.FindByName(UserName); 
     var customer = _context.Customers 
      .Include(c => c.OrderHeaders.Select(o => o.OrderLineItems.Select(i => i.Product))). 
      FirstOrDefault(c => c.UserId.Equals(user.Id)); 

     var order = customer.OrderHeaders 
      .OrderBy(o => o.OrderDate) 
      .LastOrDefault(o => o.Paid == false); 

     if(order == null) 
     { 
      order = new OrderHeader(); 
      //var Customer = new Customer(); 
      order.Customer = customer; 
      customer.OrderHeaders.Add(order); 
      _context.SaveChanges(); 
     } 
     return order; 
    } 
    } 
} 

這是視圖模型：

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

namespace SophicCeramics.Models.Order 
{ 
    public class Cart 
    { 
    public int ItemCount { get; set; } 
    public DateTime Date { get; set; } 
    public decimal Total { get; set; } 
    public List<OrderLineItem> Items { get; set; } 
    public decimal UnitPrice { get; set; } 
    public int OrderHeaderId { get; set; } 
    public string CustomerId { get; set; } 
    public System.DateTime OrderDate { get; set; } 
    public bool Paid { get; set; } 
    public int OrderLineItemId { get; set; } 
    public int ProductId { get; set; } 
    public int Quantity { get; set; } 
    public int CategoryId { get; set; } 
    public int ArtistId { get; set; } 
    public string Title { get; set; } 
    public decimal Price { get; set; } 
    public string ProductArtUrl { get; set; } 
    public string ProductArtMain { get; set; } 
    public string UserId { get; set; } 
    public string Firstname { get; set; } 
    public string Lastname { get; set; } 
    } 
} 

而且本所認爲：

@model SophicCeramics.Product 
@{ ViewBag.Title = "Cart"; } 
<div> 
<h4>Product</h4> 
<hr /> 
<dl class="dl-horizontal"> 
    <dt> 
     @Html.DisplayNameFor(model => model.Title) 
    </dt> 
    <dd> 
     @Html.DisplayFor(model => model.Title) 
    </dd> 
    <dt> 
     @Html.DisplayNameFor(model => model.Price) 
    </dt> 
    <dd> 
     @Html.DisplayFor(model => model.Price) 
    </dd> 
    <dt> 
     @Html.DisplayNameFor(model => model.ProductArtUrl) 
    </dt> 
    <dd> 
     @Html.DisplayFor(model => model.ProductArtUrl) 
    </dd> 
    <dt> 
     @Html.DisplayNameFor(model => model.ProductArtMain) 
    </dt> 
    <dd> 
     @Html.DisplayFor(model => model.ProductArtMain) 
    </dd> 
    <dt> 
     @Html.DisplayNameFor(model => model.Artist.Name) 
    </dt> 
    <dd> 
     @Html.DisplayFor(model => model.Artist.Name) 
    </dd> 
    <dt> 
     @Html.DisplayNameFor(model => model.Category.Name) 
    </dt> 
    <dd> 
     @Html.DisplayFor(model => model.Category.Name) 
    </dd> 
</dl> 
</div> 
<p> 
@Html.ActionLink("Edit", "Edit", new { id = Model.ProductId }) | 
@Html.ActionLink("Back to List", "Index") 
</p> 

視圖已經是自動佈局頁面。 我不斷收到指着這行代碼的錯誤：

var customer = _context.Customers 
     .Include(c => c.OrderHeaders.Select(o => o.OrderLineItems.Select(i => i.Product))). 
     FirstOrDefault(c => c.UserId.Equals(user.Id)); 

無論我如何重新安排包括聲明它只是將無法正常工作。 此外，控制器正在繼承另一個名爲BaseController的控制器，該控制器通過_context與數據庫建立連接。 我也試過在edmx中的.tt文件的相關類中添加幾乎所有的東西，但仍然出現錯誤。 另外，當我在customer變量上放置一個斷點並逐步完成時，它會直接轉到BaseController中的dispose方法。

Answer 1

我猜想，user爲空，所以訪問user.Id lambda表達式這裏

var customer = _context.Customers 
    .Include(c => c.OrderHeaders.Select(o => o.OrderLineItems 
    .Select(i => i.Product))) 
    .FirstOrDefault(c => c.UserId.Equals(user.Id)); 

您需要檢查是否user爲null，該行

var user = UserManager.FindByName(UserName); 

之後裏面，當你錯誤當user不爲空時，只執行FindOrCreateOrder方法內的其餘代碼。您還需要決定要怎麼做，如果user是空的else塊如下

private OrderHeader FindOrCreateOrder() 
{ 
    var UserName = this.User.Identity.Name; 
    var user = UserManager.FindByName(UserName); 
    if (user != null) 
    { 
     var customer = _context.Customers 
      .Include(c => c.OrderHeaders.Select(o => o.OrderLineItems.Select(i => i.Product))). 
      FirstOrDefault(c => c.UserId.Equals(user.Id)); 

     var order = customer.OrderHeaders 
      .OrderBy(o => o.OrderDate) 
      .LastOrDefault(o => o.Paid == false); 

     if(order == null) 
     { 
      order = new OrderHeader(); 
      //var Customer = new Customer(); 
      order.Customer = customer; 
      customer.OrderHeaders.Add(order); 
      _context.SaveChanges(); 
     } 
     return order; 
    } 
    else 
    { 
     // logic when user is null 
    } 
}