在實務上，目前自行開發一個泛型類別或函式的機會的確是不多。能想的到的範例，大致上就是利用XMLSerializer來序列化物件時可以改寫成泛型的版本吧。
利用XMLSerializer我們可以將任何型別的物件(當然會有些基本限制)給轉換成XML的格式，並儲存到檔案中。
在第一個版本中，我們實作了一個XMLPersistence類別，其中有兩個靜態函式Load()及Save()，可用來將型別為MySettings的物件儲存到指定的檔名中，或是由指定的檔名中讀取出來，還原成一個MySettings的物件。
XMLPersistence.Test()是用來測試的程式碼。說明如何使用XMLPersistence這個類別。
在做完第一版後，可以發現Load()跟Save()這兩個函式中，其實我們如果能將MySettings這個型別抽離出來，作為一個參數的話，那Load()跟Save()這兩個函式就可以改寫成泛型的函式。不論你需要儲存或讀出的型別的哪一種，都可以透過這兩個泛型函式來儲存成xml檔，或是由xml讀出轉回成物件。
程式碼下載：XMLPersistence.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.Serialization;
using System.IO;
namespace UT
{
/// <summary>
/// 要用來儲存成xml檔案的類別
/// </summary>
public class MySettings
{
public string DBName = "";
public string ServerIP = "";
public string User = "";
public string Password = "";
/// <summary>
/// xml persistence時需要預設建構子
/// </summary>
public MySettings()
{
}
public MySettings(string dbName, string serverIP, string user, string password)
{
DBName = dbName;
ServerIP = serverIP;
User = user;
Password = password;
}
public override string ToString()
{
return string.Format("DBName : {0}, ServerIP : {1}, User : {2}, Password : {3}",
DBName, ServerIP, User, Password);
}
}
/// <summary>
/// 第一版：只能處理MySettings的型別
/// </summary>
public class XMLPersistence
{
#region xml檔案存取
public static MySettings Load(string xmlFile )
{
StreamReader sr = null;
try
{
XmlSerializer xmlReader = new XmlSerializer(typeof(MySettings));
sr = new StreamReader(xmlFile, System.Text.Encoding.Default);
object tmp = xmlReader.Deserialize(sr);
if (tmp is MySettings)
{
return tmp as MySettings;
}
else
return null;
}
catch (Exception exp)
{
return null;
}
finally
{
if( sr != null )
sr.Close();
}
}
public static bool Save(string xmlFile, MySettings xmlData )
{
StreamWriter sw = null;
try
{
XmlSerializer xmlWriter = new XmlSerializer(typeof(MySettings));
sw = new StreamWriter(xmlFile, false, System.Text.Encoding.Default);
xmlWriter.Serialize(sw, xmlData );
return true;
}
catch (Exception exp)
{
return false;
}
finally
{
if( sw != null )
sw.Close();
}
}
#endregion
public static void Test()
{
MySettings setting = new MySettings( "PositionV4", "10.6.228.81", "user", "pwd" );
string filename = "TestXML.xml";
if (XMLPersistence.Save(filename, setting) == false)
{
Console.WriteLine("儲存xml失敗");
return;
}
MySettings loadFromXml = XMLPersistence.Load(filename);
if (loadFromXml != null)
{
Console.WriteLine(loadFromXml.ToString());
}
else
{
Console.WriteLine("載入xml失敗");
}
}
}
/// <summary>
/// 泛型版：可處理多種型別
/// </summary>
public class GenericXMLPersistence
{
#region xml檔案存取
/// <summary>
/// 加入class的條件式，是因為要使用到as
/// 加入new()的條件式，是因為xml可讀寫的類別要有預設建構子
/// </summary>
/// <typeparam name="TSetting"></typeparam>
/// <param name="xmlFile"></param>
/// <returns></returns>
public static TSetting Load<TSetting>(string xmlFile) where TSetting : class,new()
{
StreamReader sr = null;
try
{
XmlSerializer xmlReader = new XmlSerializer(typeof(TSetting));
sr = new StreamReader(xmlFile, System.Text.Encoding.Default);
object tmp = xmlReader.Deserialize(sr);
if (tmp is TSetting)
{
return tmp as TSetting;
}
else
return null;
}
catch (Exception exp)
{
return null;
}
finally
{
if (sr != null)
sr.Close();
}
}
public static bool Save<TSetting>(string xmlFile, TSetting xmlData) where TSetting : new()
{
StreamWriter sw = null;
try
{
XmlSerializer xmlWriter = new XmlSerializer(typeof(TSetting));
sw = new StreamWriter(xmlFile, false, System.Text.Encoding.Default);
xmlWriter.Serialize(sw, xmlData);
return true;
}
catch (Exception exp)
{
return false;
}
finally
{
if (sw != null)
sw.Close();
}
}
#endregion
public static void Test()
{
MySettings setting = new MySettings("PositionV4", "10.6.228.81", "user", "pwd");
string filename = "TestXML.xml";
if (GenericXMLPersistence.Save(filename, setting) == false)
{
Console.WriteLine("儲存xml失敗");
return;
}
// 這裏不能使用編譯器自動推論的方式，因為傳回值型別不會在進行型別推論時被使用到。
// 所以要明確指定型別
MySettings loadFromXml = GenericXMLPersistence.Load<MySettings>(filename);
if (loadFromXml != null)
{
Console.WriteLine(loadFromXml.ToString());
}
else
{
Console.WriteLine("載入xml失敗");
}
}
}
}
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