.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

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>();<br>           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 = "";<br>                    string ID = "";<br>                    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" 