将模型对象添加到列表失败

Question

我有一个像这样的模型类

  namespace ConnectBLL.DTO.Response
{
    public class CategorySettings
    {
        public bool NeedsLoginToViewLongText { get; set; }
        public bool NeedsLoginToViewAnyDetails { get; set; }
        public bool ShowAttachment { get; set; }
        public string CategoryPageID { get; set; }
        public string TpUrl { get; set; }
    }

    public class CategorySettingsListResponse
    {
        public List<CategorySettings> CategorySettingsList { get; set; }
    }
}

我正试图像这样向它添加数据

    private readonly CategorySettings cs = new CategorySettings();
 CategorySettingsListResponse csr=new CategorySettingsListResponse();
 public string GetAllCategorySettings()
    {


            cs.NeedsLoginToViewLongText = true;
            cs.NeedsLoginToViewAnyDetails = false;
            cs.ShowAttachment = true;
            cs.CategoryPageID = "1";
            cs.TpUrl = "url";
            csr.CategorySettingsList.Add(cs);

    }

但是这失败了，给出了一个错误。

Object reference not set to an instance of an object.

有人能指出我做错了什么吗？

Answer 1

在某个地方，您需要初始化CategorySettingsList。

public class CategorySettingsListResponse
{
    CategorySettingsListResponse() {
        CategorySettingsList = new List<CategorySettings>();
    }

    public List<CategorySettings> CategorySettingsList { get; set; }
}

Answer 2

在初始化之前，您要绑定到使用List实例。在此之前

csr.CategorySettingsList.Add(cs);

插入：

if (csr.CategorySettingsList == null) {
    csr.CategorySettingsList = new List<CategorySettings>();
}

Answer 3

您正在使用未创建的对象cs和CategorySettingsList，您应该在使用之前创建它们：

public string GetAllCategorySettings()
{
    csr.CategorySettingsList = new ListCategorySettings<>();
    var cs = new CategorySettings
        {
           NeedsLoginToViewLongText = true,
           ...