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[英]ASP.NET Core 5 MVC: ArgumentNullException: Value cannot be null. (Parameter 'items')
[英]"ArgumentNullException: Value cannot be null. (Parameter 'items')" using a dropdown in the view asp.net mvc to create new database records
當我嘗試創建新的數據庫記錄時,我收到錯誤“ArgumentNullException: Value cannot be null. (Parameter 'items')”。 我可以在 asp.net MVC 5 中編輯數據庫記錄,但不能創建它們。
我的模型是:
using System.ComponentModel.DataAnnotations.Schema;
namespace Speakers2.Models
{
[Table("SpeakerStatus", Schema = "SalesOps")]
public partial class SpeakerStatusLookupModel
{
public int Id { get; set; }
public string SpeakerStatus { get; set; }
}
}
上下文是:
using Microsoft.EntityFrameworkCore;
using Speakers2.Models;
namespace Speakers2.Data
{
public class Speakers2Context : DbContext
{
public Speakers2Context(DbContextOptions<Speakers2Context> options)
: base(options)
{
}
public DbSet<SpeakerStatusLookupModel> SpeakerStatusLookupModel { get; set; }
}
}
觀點是:
@model Speakers2.Models.SpeakerQuery
@{
ViewData["Title"] = "Create";
}
<h1>Create</h1>
<h4>Speaker</h4>
<hr />
<div class="row">
<div class="col-md-4">
<form asp-action="Create">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="form-group">
<label asp-for="SpeakerStatus" class="control-label"></label>
<select asp-for="SpeakerStatus" class="control-label" asp-items="@(new SelectList(@ViewBag.statusTypeList, "Id", "SpeakerStatus"))"></select>
</div>
</form>
</div>
</div>
<div>
<a asp-action="Index">Back to List</a>
</div>
@section Scripts {
@{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}
問題是<select asp-for="SpeakerStatus" class="control-label" asp-items="@(new SelectList(@ViewBag.statusTypeList, "Id", "SpeakerStatus"))"></select>
需要一個我沒有的 ID,因為我正在創建一個新記錄。
我將 @ViewBag.statusTypeList 設置為:
List<SpeakerStatusLookupModel> statusTypeList = new();
statusTypeList = (from SpeakerStatus in _context.SpeakerStatusLookupModel select SpeakerStatus).ToList();
statusTypeList.Insert(0, new SpeakerStatusLookupModel { Id = 0, SpeakerStatus = "Select" });
ViewBag.statusTypeList = statusTypeList;
我發現了問題 - 我在控制器的“編輯”部分中有 @ViewBag.statusTypeList 代碼,但在“創建”部分沒有,所以當我嘗試創建新記錄時它是 NULL。
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