将字符串分配给 ViewModel 时出现 NullReferenceException

Question

我遇到错误 NullReferenceException was unhandled by user code 后跟 Object reference not set to an instance of an object. 我已经阅读了很多问题，包括非常详细的答案 here 但不明白为什么。

行发生在行vm.HomeView.ComputerName = Environment.MachineName;

发生错误时，Environemnt.MachineName 正确显示了预期的机器名称，因此肯定有一个字符串变量正在尝试分配。

谁能帮忙解释一下原因。

控制器：

[HttpGet]
public ActionResult Index()
{
    InventoryLogViewModel vm = new InventoryLogViewModel();

    vm.HomeView.ComputerName = Environment.MachineName;
    vm.HomeView.RACFID = Environment.UserName;

    vm.AssetTypes = (from at in db.AssetTypes
                     orderby at.Name
                     select new AssetType
                     {
                         AssetTypeId = at.AssetTypeId,
                         Name = at.Name
                     }).ToList();

    return View(vm);

ViewModel:

namespace ControlsTeam.Models
{
    public class InventoryLogViewModel : _LayoutViewModel
    {
        public IEnumerable<Department> Departments { get; set; }
        public IEnumerable<AssetType> AssetTypes { get; set; }
        public Inventory Inventory { get; set; }
        public HomeView HomeView { get; set; }
    }

    public class HomeView
    {
        public string RACFID { get; set; }
        public string ComputerName { get; set; }
    }
}

Answer 1

如何，给定这段代码：

InventoryLogViewModel vm = new InventoryLogViewModel();

vm.HomeView（在下一行中使用）可以是 null 以外的任何东西吗？

InventoryLogViewModel构造函数没有实现，所以构造后其HomeView成员只能是null.

您可能需要执行以下操作：

InventoryLogViewModel vm = new InventoryLogViewModel() {
   HomeView = new HomeView() {
       RACFID = Environment.UserName,
       ComputerName = Environment.MachineName
   }
};

将字符串分配给 ViewModel 时出现 NullReferenceException

NullReferenceException when Assigning String to ViewModel

c#

asp.net-mvc

nullreferenceexception