将ASP.Net Forms标签设置为Model Property值？

Question

我正在使用ASP.NET Forms应用程序，为了简单起见，我添加了模型属性[TotalService] & [PurchasedorReinstatedService]其中我将来自另一个模型的值存储到此属性中以供第一个模型使用。

然后，我试图引用此Model属性并为其设置一个ASP标签.Text属性。问题是，我不断收到NullReferenceException异常，具体为：

An exception of type 'System.NullReferenceException' occurred in PROJECT.dll but was not handled in user code 

Additional information: Object reference not set to an instance of an object. 

这是我的自定义控制在那里我遇到了错误：

using PROJECT.Models.Default; 
using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Web; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using PROJECT.Classes; 

namespace PROJECT.CustomControls.Default 
{ 
    public partial class YearsOfService : System.Web.UI.UserControl 
    { 
     public List<Years_Of_Service> yos { get; set; } 
     public Years_Of_Service_Data yosd { get; set; } 


     protected void Page_Load(object sender, EventArgs e) 
     { 
      if (!Page.IsPostBack) 
      { 
       ApplyData(); 
      } 
     } 

     private void ApplyData() 
     { 
      salaryGridView.DataSource = yos; 
      salaryGridView.DataBind(); 

      decimal totalService = 0; 
      foreach (GridViewRow row in salaryGridView.Rows) 
      { 
       totalService += Convert.ToDecimal(row.Cells[1].Text); 
      } 

      if (yosd.YearsOfService.OrderByDescending(y => y.TotalService).FirstOrDefault().ToString() != null) // NULL REFERENCE HERE 
      { 
       creditSalLabel.Text = yosd.YearsOfService.OrderByDescending(y => y.TotalService).FirstOrDefault().ToString(); 
      } 
      else 
      { 
       creditSalLabel.Text = String.Empty; 
      } 
     } 
    } 
} 

这是我Years_Of_Service型号：

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

namespace PROJECT.Models.Default 
{ 
    public class Years_Of_Service 
    { 
     public int Year { get; set; } 
     public string FiscalYear 
     { 
      get 
      { 
       return Year + "-" + (Year + 1); 
      } 
     } 
     public decimal ServiceCredited { get; set; } 
     public decimal Salary { get; set; } 
     public string CoveredEmployer { get; set; } 

     // New properties added for Label Values 
     public string TotalService { get; set; } 
     public string PurchasedorReinstatedService { get; set; } 
    } 
} 

Years_Of_Service_Data型号：

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

namespace PROJECT.Models.Default 
{ 
    public class Years_Of_Service_Data 
    { 
     public List<Years_Of_Service> YearsOfService { get; set; } 
    } 
} 

，这是代码在我的帮助，我是从我的数据库结果（Oracle Data Reader）到我的模型实体读取位（我已确认的值越来越正确添加到TotalService & PurchasedorReinstatedService属性）：

  while (odr.Read()) 
      { 
       Years_Of_Service yosRecord = new Years_Of_Service(); 

       yosRecord.Year = gh.GetSafeInt(odr, 0); 
       yosRecord.ServiceCredited = gh.ConvertNullDecimal(odr.GetValue(1)); 
       yosRecord.Salary = gh.ConvertNullDecimal(odr.GetValue(2)); 
       yosRecord.CoveredEmployer = gh.GetSafeString(odr, 3); 

       // Use the Default Info Model Class - At_A_Glance Model properties to fill these properties for text labels. 
       yosRecord.TotalService = defInfoOasis.At_A_Glance.CreditTotal.ToString("N5"); 
       yosRecord.PurchasedorReinstatedService = defInfoOasis.At_A_Glance.TotalPurchase.ToString("N5"); 
       yos.Add(yosRecord); 
      } 

本来我尝试以下，也得到FirstOrDefault（）的实体，与NullReferenceException相同的结果：

creditSalLabel.Text = yosd.YearsOfService.OrderByDescending(y => y.TotalService).FirstOrDefault() != null ? yosd.YearsOfService.OrderByDescending(y => y.TotalService).FirstOrDefault().ToString() : String.Empty; 

purchaseCreditLabel.Text = yosd.YearsOfService.OrderByDescending(y => y.PurchasedorReinstatedService).FirstOrDefault() != null ? yosd.YearsOfService.OrderByDescending(y => y.PurchasedorReinstatedService).FirstOrDefault().ToString() : string.Empty; 

任何人有我如何可以设置我的任何想法属性给我的（任何实体）模型属性[TotalService] & [PurchasedorReinstatedService]？通过我设置属性的方式，被引用的模型类中的每个实体对这两个属性都具有相同的值。

Answer 1

我的猜测是您找回默认是空

yosd.YearsOfService.OrderByDescending(y => y.TotalService).FirstOrDefault() 

然后你正在做的ToString（）这个空。

如果不是这样，我会查看yosd为null或yosd.YearsOfService为null。