ASP.NET Core Razor Page create new for list always give System.NullReferenceException-CodePudding

when I open create new items open this page to enter the values for save to list but I always get null also inside the item there is group of item i show as drop list also give null error

in view

<input asp-for="@Model.Items.Id" />
<label asp-for="@Model.Items.Groups.Id">Group nme</label>
        <select asp-for="@Model.Items.Groups.Id"  asp-items="@(new SelectList(Model.AllGroup,"Id","GroupName" ))"></select>

in CS file

    public class Items_Class
    {
        public int Id  { get; set; }
        public string ItemName { get; set; }
        public decimal ItemPrice { get; set; }
        public decimal ItemQuantity { get; set; }
        public Groups_Class Groups { get; set; }
    }


    public class CreateModel : PageModel
    {
       private readonly Groups_Methods g_Mrthod;

       [BindProperty]
       public Items_Class Items { get; set; }
       public List<Groups_Class> AllGroup { get; set; }
       
       public CreateModel(Groups_Methods  G_Mrthod)
       {
            g_Mrthod = G_Mrthod;
          
       }    
    

       public void OnGet()
       {
           AllGroup = g_Mrthod.GetAllGroups();        
       }
   }

CodePudding user response：

I've hard time to understand your problem. What are the steps?

Load the page
Add new item
Save
Server side has null values in ItemName, ItemPrice and ItemQuantity If these are the steps, please consider adding a

public void OnPost() and read https://docs.microsoft.com/en-us/aspnet/core/razor-pages/?view=aspnetcore-6.0&tabs=visual-studio#write-a-basic-form

CodePudding user response：

You can try to set your Items and AllGroup :

[BindProperty]
        public Items_Class Items { get; set; } = new Items_Class();
        public List<Groups_Class> AllGroup { get; set; } = new List<Groups_Class>();

If it still doesn't work,try to check if g_Mrthod.GetAllGroups(); is null.