public void Delete(List EntityList) where T : class, new()

http://xdwangiflytek.iteye.com/blog/1390464 今天熟悉项目时遇到下面这段代码竟不知道什么意思，记录一下：     C#代码  

1. public T CreateViewModel<T>() where T : BaseViewModel, new()
2.     {
3.         T viewModel = new T
4.         {
5.             SiteTitle = Settings.SiteTitle,
6.             SiteDescription = Settings.SiteDescription,
7.             RootUrl = Settings.RootUrl.TrimEnd('/'),
8.             AbsolutePath = Settings.AbsolutePath.TrimEnd('\\'),
9.             MetaKeywords = Settings.MetaKeywords,
10.             MetaDescription = Settings.MetaDescription,
11.             IsCurrentUserAuthenticated = IsCurrentUserAuthenticated,
12.             CurrentUser = CurrentUser,
13.             ThemeName = ThemeName,
14.             StyleSheetUrl = GetThemeStyleSheetUrl()
15.         };
17.         if (CurrentUser != null)
18.         {
19.             viewModel.IsAdmin = CurrentUser.SysRoles.Contains(SysRoles.Administrator);
20.         }
21.         else
22.         {
23.             viewModel.IsAdmin = false;
24.         }
26.         return viewModel;
27.     }

public T CreateViewModel<T>() where T : BaseViewModel, new() { T viewModel = new T { SiteTitle = Settings.SiteTitle, SiteDescription = Settings.SiteDescription, RootUrl = Settings.RootUrl.TrimEnd('/'), AbsolutePath = Settings.AbsolutePath.TrimEnd('\\'), MetaKeywords = Settings.MetaKeywords, MetaDescription = Settings.MetaDescription, IsCurrentUserAuthenticated = IsCurrentUserAuthenticated, CurrentUser = CurrentUser, ThemeName = ThemeName, StyleSheetUrl = GetThemeStyleSheetUrl() }; if (CurrentUser != null) { viewModel.IsAdmin = CurrentUser.SysRoles.Contains(SysRoles.Administrator); } else { viewModel.IsAdmin = false; } return viewModel; }   查找后发现这是类型参数约束，.NET支持的类型参数约束有以下五种：   where T : struct | T必须是一个结构类型 where T : class T必须是一个类（class）类型 where T : new() | T必须要有一个无参构造函数 where T : NameOfBaseClass | T必须继承名为NameOfBaseClass的类 where T : NameOfInterface | T必须实现名为NameOfInterface的接口