Null 참조 오류 직접 PagedList에 목록 개체를 할당 할 때

Question

KeyMaster 모델

 public class KeyMasterModel 
     { 
      public int KeyId { get; set; } 

      public int TypeId { get; set; } 

      public string TypeName { get; set;} 

     } 

PagedKeyModel

 public class PagedKeyModel 
     { 
      // Collection of our KeyMasterModel , trying to populate this and send it to ViewModel to display a Grid// 

      public IPagedList<Security.Models.KeyMasterModel> pagedkeymaster; 
     } 

// 뷰 모델 //

  public class KeyMasterViewModel 
     { 

// 방법을 말해 생성자에서 KeyMasterViewModel.pagedkeymodel.pagedkeymaster를 초기화하면 null이되지 않습니다.

  public PagedKeyModel pagedkeymodel; 

      public KeyMasterModel keymastermodel; 

     } 

// 컨트롤러 //

    [HttpGet] 
       public ActionResult ListOfKey(string sortOrder, string CurrentSort, int? page) 
       {  

// View Model Object // 

KeyMasterViewModel keyMasterViewModel = new KeyMasterViewModel(); 


    // At the gollowing step keyMasterModelObject has values retrieved from db // 

//Next aim is to place it into ViewModel Object by assigning the retrieved PagedList of KeyMasterModel to IPagedList<Security.Models.KeyMasterModel> pagedkeymaster 


    IPagedList<KeyMasterModel> KeyMasterModelObject= datalayercall.GetAll(sortOrder, CurrentSort, page); 

    // Here is where error is thrown , all of a sudden I get the error , KeyMasterModelObject becomes null . 

    // I am trying finally to populate everything into ViewModel object 

      keyMasterViewModel .pagedkeymodel.pagedkeymaster = KeyMasterModelObject; 

      return View(keyMasterViewModel); 
     } 

// 비즈니스 로직 계층

  public IPagedList<KeyMasterModel> GetAll(string sortOrder, string CurrentSort, int? page) 
       { 

        var retrieveddatalayerobject = datalayerobject.KeyMasters; 

    // Retrieving Data from db and forming a list according to my model in App// 

        List<KeyMasterModel> keymastermodellist = new List<KeyMasterModel>(); 

        KeyMasterModel keymastermodelobject=new KeyMasterModel(); 

        foreach(var retrieveditems in retrieveddatalayerobject) 
        { 
         keymastermodelobject.KeyId = retrieveditems.KeyId; 
         keymastermodelobject.TypeName = retrieveditems.TypeMaster.TypeName; 

// Create a New List Of KeyMasterModel // 

         keymastermodellist.Add(keymastermodelobject); 
        } 

    // Paged List of KeyMaster Model // 

        IPagedList<KeyMasterModel> IPagedListKeyMasterModel = null; 

        switch (sortOrder) 
        { 

         case "KeyId": 
          if (sortOrder.Equals(CurrentSort)) 

           IPagedListKeyMasterModel = keymastermodellist.OrderByDescending 
             (m => m.KeyId).ToPagedList(pageIndex, pageSize); 

        } 

        return IPagedListKeyMasterModel; 

       } 

Answer 1

에 코드를 나는 그것을 이해 : 그래서 여기 당신이 사용하는

KeyMasterViewModel keyMasterViewModel = new KeyMasterViewModel(); 
[...] 
keyMasterViewModel.pagedkeymodel.pagedkeymaster = KeyMasterModelObject; 

을 keyMasterViewModel.pagedkeymodel이며 null이 아니라고 가정합니다 (시도했기 때문에). 그것에 속성에 할당). 그러나 KeyMasterViewModel에는 생성자가 없으므로 선언시에 pagedkeymodel을 설정하지 않으므로 기본값은 null입니다. 그러므로 당신 문제.