添加模型對象列表失敗

Question

我有這樣

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; } 
    } 
} 

模型類，我試圖將數據添加到它像這樣

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); 

    } 

但這種失敗，並給出了一個錯誤

Object reference not set to an instance of an object. 

有沒有人能指出我做錯了什麼？

Answer 1

某處，你需要初始化CategorySettingsList。

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

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

Answer 2

您正在使用受造的對象cs和CategorySettingsList，你應該使用之前創建它們：

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

Answer 3

什麼是CS？有什麼遺漏？

你忘了這樣做：

var cs = new CategorySettings(); 

而且

您需要實例化CategorySettingsList在構造函數CategorySettingsListResponse。

Answer 4

您正在初始化之前綁定使用List實例。

之前

csr.CategorySettingsList.Add(cs); 

插入：

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