.NET的值类型和引用类型

先看下微软官方介绍:

如果数据类型在它自己的内存分配中存储数据，则该数据类型就是“值类型”。“引用类型”包含指向存储数据的其他内存位置的指针。

值类型

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值类型包括：

• 所有数字数据类型

• Boolean 、Char 和 Date

• 所有结构，即使其成员是引用类型

• 枚举，因为其基础类型总是 SByte、Short、Integer、Long、Byte、UShort、UInteger 或 ULong

引用类型

---

引用类型包括：

• String

• 所有数组，即使其元素是值类型

• 类类型，如 Form

• 委托

非类型的元素

---

以下编程元素未限定为类型，因为您无法将它们中的任何一个指定为声明元素的数据类型：

• 命名空间

• 模块

• 事件

• 属性和过程

• 变量、常数和字段

如果如下这样是值类型;

int i = 10;

int j = i;

i++;

Console.Write(i);

Console.Write(j);

i的值是11,j的值是10;

如下这样DataTable传递是引用类型:

        /// <summary>
        /// 
        /// </summary>
        /// <param name="dtOriginalData"></param>
        /// <returns></returns>
        protected override DataTable TransferData(DataTable dtOriginalData)
        {
            DataTable dtFinalData = null;
            try
            {

                DataTable dtFolderData = base.ExcuteOracleReader(GetSqlQueryGetFolder);
                dtQARelate = base.ExcuteOracleReader(GetQARelateSql);               
                if (dtOriginalData != null && dtOriginalData.Rows.Count > 0)
                {
                    dtFinalData = dtOriginalData.Copy();
                    AddGlossaryToDataTable(dtFinalData);
                    AddReferencesToDataTable(dtFinalData);                   
                    AddImageUrlToDataTable(dtFinalData);
                    TransforFolderData(dtFolderData, base.SiteUrl);
                    AddProductCatagory(dtFinalData, dtFolderData);
                    this.ChangeFieldName(dtFinalData);
                }
            }
            catch (Exception ex)
            {
            }
            return dtFinalData;
        }
        private void AddImageUrlToDataTable(DataTable dtFinalData)
        {
            DataTable dtImageUrl = base.ExcuteOracleReader(GetAnswerSummarySql);

            foreach (DataRow dr in dtFinalData.Rows)
            {
                if (dtImageUrl != null && dtImageUrl.Rows.Count > 0)
                {
                    string ID = dr["ID"].ToString();
                    DataRow[] newdrs = dtImageUrl.Select(string.Format("ID='{0}'", ID));
                    dr[this.ORACLE_FIELD_ANSWER_DETAIL] += GetImageUrl(newdrs);
                }
            }
            if (dtImageUrl != null && dtImageUrl.Rows.Count > 0)
            {
                dtImageUrl.Dispose();
                dtImageUrl.Clear();
            }
        }
        private string GetImageUrl(DataRow[] drs)
        {
            string strImageUrl = "";
            if (drs != null && drs.Count() > 0)
            {
                string NewUrl = "";
                string ImageUrl = "<src img=\"{0}\"/>";
                foreach (DataRow dr in drs)
                {
                    if (dr[this.ORACLE_FIELD_ANSWER_ImageURL] != null && !string.IsNullOrEmpty(dr[this.ORACLE_FIELD_ANSWER_ImageURL].ToString()))
                    {

                        NewUrl = dr[this.ORACLE_FIELD_ANSWER_ImageURL].ToString();

                        strImageUrl += "<br />" + string.Format(ImageUrl, NewUrl);
                    }
                }
            }
            return strImageUrl;
        }



        protected override List<SingleResultBE> ModifyQARelateAndRelateBy(List<SingleResultBE> newlistResult)
        {
            List<SingleResultBE> onelistResult = new List<SingleResultBE>();
           foreach (SingleResultBE entity in newlistResult)
            {
                if (!string.IsNullOrEmpty(entity.Id) && !string.IsNullOrEmpty(entity.ListItemId.ToString()))
                {
                    DataRow[] newdrs = dtQARelate.Select(string.Format("ID='{0}'", entity.Id));
                    if (newdrs != null && newdrs.Count() > 0)
                        entity.QARelate = GetQARelate(newdrs, newlistResult);
                    DataRow[] otherdrs = dtQARelate.Select(string.Format("RELATEID='{0}'", entity.Id));
                    if (otherdrs != null && otherdrs.Count() > 0)
                        entity.RelateBy = GetQARelateBy(otherdrs, newlistResult);
                    onelistResult.Add(entity);
                }

            }
            if (dtQARelate != null && dtQARelate.Rows.Count > 0)
            {
                dtQARelate.Dispose();
                dtQARelate.Clear();
            }
            return onelistResult;
        }


        #endregion

        #region Private Methods

        private string GetQARelateBy(DataRow[] drs, List<SingleResultBE> newlistResult)
        {
            string strQARelateBy = "";
            foreach (DataRow dr in drs)
            {
                string strQARelateID = "";
                string strTitle = "";

                if (dr[this.ORACLE_FIELD_ID] != null)
                    strQARelateID = dr[this.ORACLE_FIELD_ID].ToString();

                if (dr[this.ORACLE_FIELD_TITLE] != null)
                {
                    strTitle = dr[this.ORACLE_FIELD_TITLE].ToString();
                }
                List<SingleResultBE> needlistfolder = new List<SingleResultBE>();
                if (!string.IsNullOrEmpty(strTitle) && !string.IsNullOrEmpty(strQARelateID))
                    needlistfolder = GetlistResult(newlistResult, strTitle, strQARelateID);
                if (needlistfolder != null && needlistfolder.Count > 0)
                {
                    strQARelateBy += GetlistItemGuid(needlistfolder[0].ListItemGuid);
                }

            }
            return strQARelateBy;
        }
        private string GetQARelate(DataRow[] drs, List<SingleResultBE> newlistResult)
        {
            string strQARelate = "";


            foreach (DataRow dr in drs)
            {
                string strQARelateID = "";
                string strTitle = "";

                if (dr[this.ORACLE_FIELD_QARELATEDID] != null)
                    strQARelateID = dr[this.ORACLE_FIELD_QARELATEDID].ToString();

                if (dr[this.ORACLE_FIELD_QARELATED_TITLE] != null)
                    strTitle = dr[this.ORACLE_FIELD_QARELATED_TITLE].ToString();
                List<SingleResultBE> needlistfolder = new List<SingleResultBE>();
                if (!string.IsNullOrEmpty(strTitle) && !string.IsNullOrEmpty(strQARelateID))
                    needlistfolder = GetlistResult(newlistResult, strTitle, strQARelateID);
                if (needlistfolder != null && needlistfolder.Count > 0)
                {
                    strQARelate += GetlistItemGuid(needlistfolder[0].ListItemGuid);
                }

            }
            return strQARelate;
        }


        private void AddProductCatagory(DataTable dtFinalData, DataTable dtFolderData)
        {
            dtFinalData.Columns[this.ORACLE_FIELD_PRODUCT_CATEGORY].MaxLength = 99999;
            foreach (DataRow dr in dtFinalData.Rows)
            {
                if (dtFolderData != null && dtFolderData.Rows.Count > 0)
                {
                    string ID = dr["ID"].ToString();
                    DataRow[] newdrs = dtFolderData.Select(string.Format("ID='{0}'", ID));
                    dr[this.ORACLE_FIELD_PRODUCT_CATEGORY] = GetProductCatagory(newdrs, dtFolderData);
                }
            }
        }
        private string GetProductCatagory(DataRow[] drs, DataTable dtFolderData)
        {
            List<SingleResultBE> listResult = new List<SingleResultBE>();
            listResult.AddRange(HavelistResult);
            string strProductCatagory = "";
            if (drs != null && drs.Count() > 0)
            {
                foreach (DataRow dr in drs)
                {
                    string foldername = "";
                    string folderID = "";
                    string ID = "";
                    if (dr[this.ORACLE_FIELD_FOLDERID] != null)
                        folderID = dr[this.ORACLE_FIELD_FOLDERID].ToString();
                     DataRow[] drfolders = dtFolderData.Select(string.Format("FOLDERID='{0}'", folderID));
                    List<SingleResultBE> needlistfolder = new List<SingleResultBE>();
                    foreach (DataRow drf in drfolders)
                    {
                        List<SingleResultBE> Islistfolder = new List<SingleResultBE>();
                        foldername = drf[this.ORACLE_FIELD_FATHERTITLE].ToString();
                        ID = drf[this.ORACLE_FIELD_FOLDERID].ToString();
                        if (!string.IsNullOrEmpty(ID))
                        {
                            Islistfolder = GetlistResult(listResult, foldername, ID);
                            if (Islistfolder != null && Islistfolder.Count() > 0)
                                needlistfolder.AddRange(Islistfolder);
                        }
                        if (needlistfolder.Count > 0)
                            needlistfolder = needlistfolder.Distinct().ToList();
                    }
                    if (needlistfolder != null && needlistfolder.Count > 0)
                    {
                        foreach (SingleResultBE entity in needlistfolder)
                        {
                            strProductCatagory += GetlistItemGuid(entity.ListItemGuid.ToString());
                        }
                    }

                }
            }

            return strProductCatagory;
        }

        private string GetlistItemGuid(string itemguid)
        {
            if (!string.IsNullOrEmpty(itemguid))
            {
                int startindex = itemguid.IndexOf(startwith) + 1;
                int endindex = itemguid.IndexOf(endwith);
                return itemguid.Substring(startindex, endindex - startindex).ToLower() + ";#";
            }
            return null;
        }


        private List<SingleResultBE> GetlistResult(List<SingleResultBE> listResult, string title, string ID)
        {

            List<SingleResultBE> needlistfolder = new List<SingleResultBE>();
            if (!string.IsNullOrEmpty(title))
            {
                needlistfolder = (from entity in listResult
                                  where entity.Title == title && entity.Id == ID
                                  select entity).ToList();
            }
            return needlistfolder;
        }

还有如下也是引用类型:

///新建一个类
 public class FolderBE
    {
       public string FolderOne
       { get; set; }
       public string FolderTwo
       { get; set; }
       public string FolderThree
       { get; set; }
       public string FolderFour
       { get; set; }
       public string FolderFive
       { get; set; }
    }

//然后:
         List<FolderBE> listFolder = new List<FolderBE>();

                    FolderBE folder = new FolderBE();
                    folder.FolderOne = "one";
                    folder.FolderTwo = "two";
                    folder.FolderThree = "three";

                    listFolder.Add(folder);

                    folder.FolderFour = "four";

  ///然后listFolder里的一条数据的FolderFour也会变成"four";

///   所以我们在使用它时要这样:

                     List<FolderBE> listFolder = new List<FolderBE>();

                    FolderBE folder = new FolderBE();
                    folder.FolderOne = "one";
                    folder.FolderTwo = "two";
                    folder.FolderThree = "three";

                    listFolder.Add(folder);

                  folder = new FolderBE();
                    folder.FolderOne = "one";
                    folder.FolderTwo = "two";
                    folder.FolderThree = "three";

                    folder.FolderFour = "four";

///listFolder里面的数据 FolderFour不会变成"four" 

先写到这里吧.