Question

检查下面的代码。我想将列表值设置为StorageFileDisplay类的MainFolderDisplay类。所以我想在控制器中做的是- var mainFolder初始化MainFolderDisplay类，然后尝试访问名为SubFolderDisplay的列表内的StorageFileDisplay，然后尝试为该StorageFileDisplay列表设置新值。但是当前代码的问题在于它无法访问mainFolder.SubFolderDisplay.StorageFileDisplay并引发异常-

实例未设置为对象的实例

任何人都可以告诉我如何从称为SubFolderDisplay.StorageFileDisplay.StorageFileDisplay的主要指标中为MainFolderDisplay列表增加价值？预先感谢

控制器：

var mainFolder = new MainFolderDisplay();

mainFolder.SubFolderDisplay.StorageFileDisplay.Add(new StorageFileDisplay
{
    AwsUniqueFileName = "foo",
    FileId = 0,
    FolderType = 0,
    RelatedFolderId = 0,
    UserDisplayFileName = "foo",
    UserId = 0,
});

型号：

using Test.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Test.ViewModels
{
    public class MainFolderDisplay
    {
        public int MainFolderId { get; set; }
        public string MainFolderName { get; set; }
        public int UserId { get; set; }

        public List<StorageFileDisplay> StorageFileDisplay { get; set; }
        public List<SubFolderDisplay> SubFolderDisplay { get; set; }
    }

    public class SubFolderDisplay
    {
        public int SubFolderId { get; set; }
        public string SubFolderName { get; set; }
        public int MainFolderId { get; set; }
        public List<StorageFileDisplay> StorageFileDisplay { get; set; }
    }

    public class StorageFileDisplay
    {

        public int FileId { get; set; }
        public string AwsUniqueFileName { get; set; }
        public string UserDisplayFileName { get; set; }
        public int UserId { get; set; }
        public int FolderType { get; set; }
        public int RelatedFolderId { get; set; }
    }
}

Answer 1

您还必须实例化所有嵌套属性，默认情况下它们为null。试试这个：

var mainFolder = new MainFolderDisplay
{
    SubFolderDisplay = new List<SubFolderDisplay>
    {
        new SubFolderDisplay
        {
            StorageFileDisplay = new List<StorageFileDisplay>
            {
                new StorageFileDisplay
                {
                    AwsUniqueFileName = "foo",
                    FileId = 0,
                    FolderType = 0,
                    RelatedFolderId = 0,
                    UserDisplayFileName = "foo",
                    UserId = 0,
                }
            }
        }
    }
};

Answer 2

实例未设置为对象的实例。

这显然是您在尝试对实际上为空的内容执行操作。

这意味着您在StorageFileDisplay对象中的SubFolderDisplay和MainFolderDisplay列表为空。因此，首先您必须初始化这些列表。您可以在MainFolderDisplay类中进行以下操作：

public class MainFolderDisplay
{
        public MainFolderDisplay()
        {
            StorageFileDisplay = new List<StorageFileDisplay>();
            SubFolderDisplay = new List<SubFolderDisplay>();
        }
        public int MainFolderId { get; set; }
        public string MainFolderName { get; set; }
        public int UserId { get; set; }

        public List<StorageFileDisplay> StorageFileDisplay { get; set; }
        public List<SubFolderDisplay> SubFolderDisplay { get; set; }
}

Answer 3

我认为SubFolderDisplay或StorageFileDisplay列表未实例化。确保在添加

之前

new List<SubFolderDisplay>()
new List<StorageFileDisplay>()

在主类的子类列表值中设置子

3 个答案: