一起谈.NET技术，C# 基础概念之延迟加载

class Program
{
static void Main( string [] args)
{
/// 这行代码表明：要创建一个延迟加载的字符串对象s
/// 原型为Lazy <T> 对象名=new Lazy <T> (Fun <T> )
/// 采用泛型委托进行构造，实例化此委托时要求必须是返回值T类型的方法
/// 如在本例中，T为string，则TestLazy.GetString方法的返回值必须也是string类型
Lazy < string > s = new Lazy < string > (TestLazy.GetString);
Console.WriteLine(s.IsValueCreated); // 返回False
Console.WriteLine(s.Value); // 返回S的当前值
Console.WriteLine(s.IsValueCreated); // 返回True
}
}
public class TestLazy
{
public static string GetString()
{
return DateTime.Now.ToLongTimeString();
}
}

class Program
{
static void Main( string [] args)
{
BlogUser blogUser = new BlogUser( 1 );
Console.WriteLine( " blogUser has been initialized " );

foreach (var article in blogUser.Articles.Value)
{
Console.WriteLine(article.Title);
}
}
}

public class BlogUser
{
public int Id { get ; private set ; }
public Lazy < List < Article >> Articles { get ; private set ; }
public BlogUser( int id)
{
this .Id = id;
Articles = new Lazy < List < Article >> (() => ArticleServices.GetArticesByID(id));
Console.WriteLine( " BlogUser Initializer " );
}
}
public class Article
{
public int Id { get ; set ; }
public string Title{ get ; set ;}
public DateTime PublishDate { get ; set ; }
}
public class ArticleServices
{
public static List < Article > GetArticesByID( int blogUserID)
{
List < Article > articles = new List < Article > {
new Article{Id = 1 ,Title = " Lazy Load " ,PublishDate = DateTime.Parse( " 2011-4-20 " )},
new Article{Id = 2 ,Title = " Delegate " ,PublishDate = DateTime.Parse( " 2011-4-21 " )},
new Article{Id = 3 ,Title = " Event " ,PublishDate = DateTime.Parse( " 2011-4-22 " )},
new Article{Id = 4 ,Title = " Thread " ,PublishDate = DateTime.Parse( " 2011-4-23 " )}
};
Console.WriteLine( " Article Initalizer " );
return articles;
}
}