System.NullReferenceException - 帮助

Question

我的.NET可能会生锈但我不能在这里找出问题。

我知道它有一个错误，因为我没有检查“null”异常，但我不知道为什么它是null。

tNewObjFolder.cmdSets为null，但是是ICollection，所以我应该能够使用Add将tNewObjCmdSet添加到右边吗？

如果我删除了foreach（ * 中的var tCmdSets），它可以工作（但是我很可能没有运行第二个foreach，并且从不尝试向cmdSets.Add添加任何内容功能...

任何帮助都是适当的。

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel.DataAnnotations;
using System.Globalization;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Data;
using System.Data.Entity;
using System.Data.Objects;


namespace imageController.Models
{
public class settingsModels
{
    public class objFolder
    {
        public decimal id { get; set; }
        public string name { get; set; }
        public string description { get; set; }
        public string bulkDirectory { get; set; }
        public ICollection<objCmdSet> cmdSets { get; set; }
    }
    public class objCmdSet
    {
        public decimal id { get; set; }
        public string name { get; set; }
        public string command { get; set; }
        public string destination { get; set; }
        public string filetype { get; set; }
        public decimal? imageId { get; set; }
        public decimal? folderId { get; set; }
    }
    public interface ISettingsService
    {
        List<objFolder> getFolders();
    }
    public class settingsServices : ISettingsService
    {
        private settingsEntities _entities = new settingsEntities();

        public List<objFolder> getFolders()
        {
            ICollection<objFolder> tmpFolders = new Collection<objFolder>();

            foreach (var tFolders in _entities.IMG_SETTINGS_FOLDERS)
            {
                objFolder tNewObjFolder = new objFolder();
                tNewObjFolder.id = tFolders.SETTINGS_FOLDER_ID;
                tNewObjFolder.name = tFolders.SETTINGS_FOLDER_NAME;
                tNewObjFolder.description = tFolders.SETTINGS_FOLDER_DESCRIPTION;
                tNewObjFolder.bulkDirectory = tFolders.SETTINGS_FOLDER_BULK;

                foreach (var tCmdSets in _entities.IMG_SETTINGS_CMDSETS.Where("it.SETTINGS_FOLDER_ID = @folderid", new ObjectParameter("folderid",tFolders.SETTINGS_FOLDER_ID)))
                {
                    objCmdSet tNewObjCmdSet = new objCmdSet();
                    tNewObjCmdSet.id = tCmdSets.SETTINGS_CMDSET_ID;
                    tNewObjCmdSet.name = tCmdSets.SETTINGS_CMDSET_NAME;
                    tNewObjCmdSet.command = tCmdSets.SETTINGS_CMDSET_COMMAND;
                    tNewObjCmdSet.destination = tCmdSets.SETTINGS_CMDSET_DESTINATION;
                    tNewObjCmdSet.filetype = tCmdSets.SETTINGS_CMDSET_FILETYPE;
                    tNewObjCmdSet.imageId = tCmdSets.SETTINGS_IMAGETYPE_ID;
                    tNewObjCmdSet.folderId = tCmdSets.SETTINGS_FOLDER_ID;
                    tNewObjFolder.cmdSets.Add(tNewObjCmdSet);
                }
                tmpFolders.Add(tNewObjFolder);
            }
            return tmpFolders.ToList<objFolder>();
        }
    }
}

}

Answer 1

你的问题似乎在这里......

tNewObjFolder.cmdSets.Add(tNewObjCmdSet);

你无处可以实现cmdSets集合......

编辑for循环以显示..。

if(tNewObjFolder.cmdSets == null) tNewObjFolder.cmdSets = new Collection<objCmdSet>();
tNewObjFolder.objFolder.Add(tNewObjCmdSet);

或者在objFolder类中添加一个构造函数来初始化构造中的集合......

public objFolder()
{
    cmdSets = new Collection<objCmdSet>();
}

Answer 2

您可以对空集合使用.Add()，而不是null。您必须区分这两件事并按照iDevForFun的建议处理null。