foreach循环和泛型类 [英] foreach loop and generic class
问题描述
我是仿制药的新手。我写了一个简单的类，我通过一个通用列表来获得
。我能够通过列表甚至传递列表的
类型，以便我可以使用它来遍历它。这是一个通用列表
的业务对象。我能够在调试器中看到类型是正确的
。
但是当我尝试使用类型I遍历列表时不能
编译。我已验证在调试器中正确传递
的相同类型变量给出错误：
类型或命名空间rectype无法找到。
当我尝试在foreach循环中使用它时会发生这种情况。我尝试了实现IEnumerabler的
但是从那里得到了编译错误。这是
代码。正如你所看到的，我已经注意到了令人讨厌的foreach循环。在
调试器中，我可以看到rectype是正确的底层类型，但
我可以在foreach循环中使用它：
使用System;
使用System.Data;
使用System.Configuration;
使用System.Web;
使用System.Web.Security;
使用System.Web.UI;
使用System.Web.UI.WebControls;
使用System .Web.UI.WebControls.WebParts;
使用System.Web.UI.HtmlControls;
使用System.Collections.Generic;
使用System.Reflection;
///< summary>
/// BusinessObjectsGeneric的摘要描述
///< / summary>
公共类BusinessObjectsGeneric< T>
{
public BusinessObjectsGeneric（）
{
//
// TODO：在这里添加构造函数逻辑
//
}
public DataTable ReturnObjectCollectioAsTable（List< TGenList，Type
typ）
{
if（GenList == null）
返回null;
DataTable dt = new DataTable（）;
PropertyInfo [] pi = typ.GetProperties（）;
foreach（PropertyInfo p in pi）
{
dt.Columns.Add（new DataColumn（p.Name，p.PropertyType））;
}
类型def = typeof（BusinessObjectsGeneric< T>）;
类型rectype = typ;
// foreach（GenList中的rectype项目）
// {
//}
返回dt;
}
}
任何帮助都将不胜感激。
Fig000
I''m new to generics. I''ve written a simple class to which I''m
passing a generic list. I''m able to pass the list and even pass the
type of the list so I can use it to traverse it. It''s a generic list
of business objects. I''m able to see that the type is the correct one
in the debugger.
However when I try to traverse the list using the type I can''t
compile. The same type variable I''ve verified as being passed
correctly in the debugger gives the error:
The type or namespace "rectype" could not be found.
This happens when I try to use it in a foreach loop. I tried
implementing IEnumerabler but got compile error from that. Here is the
code. As you can see I''ve commented out the offending foreach loop. In
the debugger I can see that rectype is the correct underlying type but
I can use it in the foreach loop:
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;
using System.Reflection;
/// <summary>
/// Summary description for BusinessObjectsGeneric
/// </summary>
public class BusinessObjectsGeneric<T>
{
public BusinessObjectsGeneric()
{
//
// TODO: Add constructor logic here
//
}
public DataTable ReturnObjectCollectioAsTable(List<TGenList,Type
typ)
{
if (GenList == null)
return null;
DataTable dt = new DataTable();
PropertyInfo[] pi = typ.GetProperties();
foreach (PropertyInfo p in pi)
{
dt.Columns.Add(new DataColumn(p.Name, p.PropertyType));
}
Type def = typeof(BusinessObjectsGeneric<T>);
Type rectype = typ;
// foreach (rectype item in GenList)
// {
// }
return dt;
}
}
Any help would be appreciated.
Fig000
推荐答案
2007-11-12 16:15:08 -0800，fig000< ne *********** @ yahoo.comsaid：
On 2007-11-12 16:15:08 -0800, fig000 <ne***********@yahoo.comsaid:
HI，
我是仿制药的新手。我写了一个简单的类，我通过一个通用列表来获得
。我能够通过列表甚至传递列表的
类型，以便我可以使用它来遍历它。这是一个通用列表
的业务对象。我能够在调试器中看到类型是正确的
。
但是当我尝试使用类型I遍历列表时不能
编译。我已验证在调试器中正确传递
的相同类型变量给出错误：
类型或命名空间rectype无法找到。
I''m new to generics. I''ve written a simple class to which I''m
passing a generic list. I''m able to pass the list and even pass the
type of the list so I can use it to traverse it. It''s a generic list
of business objects. I''m able to see that the type is the correct one
in the debugger.
However when I try to traverse the list using the type I can''t
compile. The same type variable I''ve verified as being passed
correctly in the debugger gives the error:
The type or namespace "rectype" could not be found.
那么，你究竟想要做什么？
你得到的错误是因为rectype实际上并不是一种可以使用的类型
用于变量声明。它是Type类型的类实例。
你可以写这样的东西：
foreach（GenList中的T项）
{
}
然后这就引出了一个问题：你将用item做什么？循环内部？
为什么要将Type作为参数传递给方法，以及你真的想用这个参数怎么样？
？
Pete
Well, what exactly are you actually trying to do?
You get the error because "rectype" isn''t actually a type you can use
for a variable declaration. It''s a class instance of type Type.
You could write something like this:
foreach (T item in GenList)
{
}
but then that begs the question: what will you do with "item" inside the loop?
Why are you passing a Type as a parameter to the method, and how is it
that you really want to use that parameter?
Pete
你有一个类型为T的通用列表：
List< ; TGenList; // =新列表< T>（）;
此列表的每种语法都是
：
foreach（GenList中的T项）
{
//用物品做的东西。
}
" fig000" < ne *********** @ yahoo.com写了留言
新闻：11 ******************* *@19g2000hsx.googlegroup s.com ...
You have a generic list of type T:
List<TGenList; // = new List<T>();
for each syntax for this list is:
foreach( T item in GenList )
{
// do stuff with the item.
}
"fig000" <ne***********@yahoo.comwrote in message
news:11********************@19g2000hsx.googlegroup s.com...
HI，
我是仿制药的新手。我写了一个简单的类，我通过一个通用列表来获得
。我能够通过列表甚至传递列表的
类型，以便我可以使用它来遍历它。这是一个通用列表
的业务对象。我能够在调试器中看到类型是正确的
。
但是当我尝试使用类型I遍历列表时不能
编译。我已验证在调试器中正确传递
的相同类型变量给出错误：
类型或命名空间rectype无法找到。
当我尝试在foreach循环中使用它时会发生这种情况。我尝试了实现IEnumerabler的
但是从那里得到了编译错误。这是
代码。正如你所看到的，我已经注意到了令人讨厌的foreach循环。在
调试器中，我可以看到rectype是正确的底层类型，但
我可以在foreach循环中使用它：
使用System;
使用System.Data;
使用System.Configuration;
使用System.Web;
使用System.Web.Security;
使用System.Web.UI;
使用System.Web.UI.WebControls;
使用System .Web.UI.WebControls.WebParts;
使用System.Web.UI.HtmlControls;
使用System.Collections.Generic;
使用System.Reflection;
///< summary>
/// BusinessObjectsGeneric的摘要说明
///< ; / summary>
公共类BusinessObjectsGeneric< T>
{
public BusinessObjectsGeneric（）
{
//
// TODO：在这里添加构造函数逻辑
//
}
public DataTable ReturnObjectCollectioAsTable（List< TGenList，Type
typ）
{
if（GenList == null）
返回null;
DataTable dt = new DataTable（）;
PropertyInfo [] pi = typ.GetProperties（）;
foreach（PropertyInfo p in pi）
{
dt.Columns.Add（new DataColumn（p.Name，p.PropertyType））;
}
类型def = typeof（BusinessObjectsGeneric< T>）;
类型rectype = typ;
// foreach （GenList中的rectype项目）
// {
//}
return dt;
}
}
任何帮助都将不胜感激。
Fig000
I''m new to generics. I''ve written a simple class to which I''m
passing a generic list. I''m able to pass the list and even pass the
type of the list so I can use it to traverse it. It''s a generic list
of business objects. I''m able to see that the type is the correct one
in the debugger.
However when I try to traverse the list using the type I can''t
compile. The same type variable I''ve verified as being passed
correctly in the debugger gives the error:
The type or namespace "rectype" could not be found.
This happens when I try to use it in a foreach loop. I tried
implementing IEnumerabler but got compile error from that. Here is the
code. As you can see I''ve commented out the offending foreach loop. In
the debugger I can see that rectype is the correct underlying type but
I can use it in the foreach loop:
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;
using System.Reflection;
/// <summary>
/// Summary description for BusinessObjectsGeneric
/// </summary>
public class BusinessObjectsGeneric<T>
{
public BusinessObjectsGeneric()
{
//
// TODO: Add constructor logic here
//
}
public DataTable ReturnObjectCollectioAsTable(List<TGenList,Type
typ)
{
if (GenList == null)
return null;
DataTable dt = new DataTable();
PropertyInfo[] pi = typ.GetProperties();
foreach (PropertyInfo p in pi)
{
dt.Columns.Add(new DataColumn(p.Name, p.PropertyType));
}
Type def = typeof(BusinessObjectsGeneric<T>);
Type rectype = typ;
// foreach (rectype item in GenList)
// {
// }
return dt;
}
}
Any help would be appreciated.
Fig000
你不需要传入实际的类型。你只需要完全支持Generics这个
方法。请尝试这样做：
public DataTable ReturnObjectCollectionAsTable< T>（List< TGenList）
{
foreach（GenList中的T项） ）
{
//代码在这里
}
}
如果你需要确保T是一个实现某种类型的
接口的类，或者扩展某种类型的对象，你可以使用where子句约束函数
public DataTable ReturnObjectCollectionAsTable< T>（List< TGenList）其中T
：IDisposable //或任何其他基类或接口
-
Andrew Faust
andrew [at] andrewfaust.com
http://www.andrewfaust.com
" fig000" < ne *********** @ yahoo.com写了留言
新闻：11 ******************* *@19g2000hsx.googlegroup s.com ...
You don''t need to pass in the actual Type. You just need to make this
method support Generics fully. Try this instead:
public DataTable ReturnObjectCollectionAsTable<T>(List<TGenList)
{
foreach (T item in GenList)
{
//Code Here
}
}
If you need to make sure T is a class that implements a certain type of
interface or extends some type of object you can constrain the function
with a where clause
public DataTable ReturnObjectCollectionAsTable<T>(List<TGenList) where T
: IDisposable //Or any other base classes or Interfaces
--
Andrew Faust
andrew[at]andrewfaust.com
http://www.andrewfaust.com
"fig000" <ne***********@yahoo.comwrote in message
news:11********************@19g2000hsx.googlegroup s.com...
HI，
我是仿制药的新手。我写了一个简单的类，我通过一个通用列表来获得
。我能够通过列表甚至传递列表的
类型，以便我可以使用它来遍历它。这是一个通用列表
的业务对象。我能够在调试器中看到类型是正确的
。
但是当我尝试使用类型I遍历列表时不能
编译。我已验证在调试器中正确传递
的相同类型变量给出错误：
类型或命名空间rectype无法找到。
当我尝试在foreach循环中使用它时会发生这种情况。我尝试了实现IEnumerabler的
但是从那里得到了编译错误。这是
代码。正如你所看到的，我已经注意到了令人讨厌的foreach循环。在
调试器中，我可以看到rectype是正确的底层类型，但
我可以在foreach循环中使用它：
使用System;
使用System.Data;
使用System.Configuration;
使用System.Web;
使用System.Web.Security;
使用System.Web.UI;
使用System.Web.UI.WebControls;
使用System .Web.UI.WebControls.WebParts;
使用System.Web.UI.HtmlControls;
使用System.Collections.Generic;
使用System.Reflection;
///< summary>
/// BusinessObjectsGeneric的摘要说明
///< ; / summary>
公共类BusinessObjectsGeneric< T>
{
public BusinessObjectsGeneric（）
{
//
// TODO：在这里添加构造函数逻辑
//
}
public DataTable ReturnObjectCollectioAsTable（List< TGenList，Type
typ）
{
if（GenList == null）
返回null;
DataTable dt = new DataTable（）;
PropertyInfo [] pi = typ.GetProperties（）;
foreach（PropertyInfo p in pi）
{
dt.Columns.Add（new DataColumn（p.Name，p.PropertyType））;
}
类型def = typeof（BusinessObjectsGeneric< T>）;
类型rectype = typ;
// foreach （GenList中的rectype项目）
// {
//}
return dt;
}
}
任何帮助都将不胜感激。
Fig000
I''m new to generics. I''ve written a simple class to which I''m
passing a generic list. I''m able to pass the list and even pass the
type of the list so I can use it to traverse it. It''s a generic list
of business objects. I''m able to see that the type is the correct one
in the debugger.
However when I try to traverse the list using the type I can''t
compile. The same type variable I''ve verified as being passed
correctly in the debugger gives the error:
The type or namespace "rectype" could not be found.
This happens when I try to use it in a foreach loop. I tried
implementing IEnumerabler but got compile error from that. Here is the
code. As you can see I''ve commented out the offending foreach loop. In
the debugger I can see that rectype is the correct underlying type but
I can use it in the foreach loop:
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;
using System.Reflection;
/// <summary>
/// Summary description for BusinessObjectsGeneric
/// </summary>
public class BusinessObjectsGeneric<T>
{
public BusinessObjectsGeneric()
{
//
// TODO: Add constructor logic here
//
}
public DataTable ReturnObjectCollectioAsTable(List<TGenList,Type
typ)
{
if (GenList == null)
return null;
DataTable dt = new DataTable();
PropertyInfo[] pi = typ.GetProperties();
foreach (PropertyInfo p in pi)
{
dt.Columns.Add(new DataColumn(p.Name, p.PropertyType));
}
Type def = typeof(BusinessObjectsGeneric<T>);
Type rectype = typ;
// foreach (rectype item in GenList)
// {
// }
return dt;
}
}
Any help would be appreciated.
Fig000
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