通用接口和运行时对象的转换问题 [英] Generic Interfaces and casting from object at runtime problem

问题描述

让我们说我想要一个支持Min / Max

属性的泛型类型，如果需要，可以是double或整数甚至是datetime，

灵活的东西。


所以我开始创建以下通用接口：


*注意：实际上我实现了IComparable和IEquatable泛型

接口和相关的覆盖方法，但是我已经将这个例子的所有内容减少到了最低限度。


public界面IMinMax< T>

{

T Min {get;}

T Max {get;}

} $ / $

和以下通用结构：

public struct MinMax< T：IMinMax< T>

{

私人读取T min;

私人读取T max;


public T Min

{

get

{

返回分钟;

}

}


public T Max

{

get

{

返回最大值;

}

}


公共MinMax（T min，T max）

{

this.min = min;

this.max = max;

}


}

现在这里有一些使用它的代码：

IMinMax< intintMinMax = new MinMax< int>（ 0,100）; //百分比范围

IMinMax< ddateMinMax = new MinMax< DateTime>（new DateTime（1973,10，

4），DateTime.Now）; //日期范围

好​​的，所以这就是问题......如果我有以下

程序怎么办？


public void DoSomething（object o）

{

IMinMax< mm =（IMinMax<>）o; //这个不行吗


//用mm.Min和mm.Max做点什么

}


我想按如下方式调用该程序：


DoSomething（intMinMax）;

DoSomething（dateMinMax）;

我们如何与Min和Max做点什么？显然，代码中缺少了很多肉，而且我为了这个新闻组的目的而将其简化为非常简单的

所以请不要

问我为什么要这样做...这会以一种或另一种形式出现所有

时间。


我猜真实问题是......一旦你将一个通用界面

投射到一个对象上，你如何在run-

时间内提取它的信息呢？在我的情况下，我碰巧在运行时知道类型，但是修改后的方法后面的

仍然不起作用：


public void DoSomething（Type t，对象o）

{

IMinMax< tmm =（IMinMax< t>）o; //仍然无法工作


//用mm.Min和mm.Max做点什么

}

问候！


Anthony

Let''s say that I would like a generic type that supports Min/Max
properties and can be double or integer or even datetime if need be,
something flexible.

So I go about creating the following generic interface :

*note : in reality I implement the IComparable and IEquatable generic
interfaces and associated overriden methods, but I''ve cut everything
down to the bare minimum for this example.

public interface IMinMax<T>
{
T Min{get;}
T Max{get;}
}

and the following generic struct :

public struct MinMax<T: IMinMax<T>
{
private readonly T min;
private readonly T max;

public T Min
{
get
{
return min;
}
}

public T Max
{
get
{
return max;
}
}

public MinMax(T min, T max)
{
this.min = min;
this.max = max;
}

}
Now here''s some code to use it :

IMinMax<intintMinMax = new MinMax<int>(0, 100); // percentage range
IMinMax<ddateMinMax = new MinMax<DateTime>(new DateTime(1973, 10,
4), DateTime.Now); // date range
Okay, so here''s the problem... what if I have the following
procedure :

public void DoSomething(object o)
{
IMinMax<mm = (IMinMax<>) o; // this doesn''t work

// do something with mm.Min and mm.Max here
}

and I want to call the procedure as follows :

DoSomething(intMinMax);
DoSomething(dateMinMax);
How do we go about doing something with Min and Max? Obviously there''s
a lot of meat missing in the code and I simplified it quite
unrealistically for the purpose of this newsgroup so please no
questions as to why I would want to do it... this comes up all the
time in one form or another.

I guess the real question is... once you''ve cast a generic interface
to an object, how do you go about extracting its information at run-
time? In my case I happen to know the type at runtime but the
following modified method still doesn''t work :

public void DoSomething(Type t, object o)
{
IMinMax<tmm = (IMinMax<t>) o; // still doesn''t work

// do something with mm.Min and mm.Max here
}
Regards!

Anthony

推荐答案

你的结构（或价值类型）是盒装的类型信息似乎丢失

转换为对象时..

您可以尝试C ++ / CLI，它会在您输入值时保留类型信息

类型。

参考

C ++：Kenny最强大的.NET框架编程语言

Kerr，MSDN

-

盛江

VC ++中的微软MVP

" Anthony Paul" < a ********** @ gmail.comwrote in message

news：11 ******************** **@o11g2000prd.googlegr oups.com ...

Your struct (or value type) is boxed and the type information seems lost
when it is converted to object..
You can try C++/CLI, which retains type information when you box a value
type.
Reference
C++: The Most Powerful Language for .NET Framework Programming by Kenny
Kerr, MSDN
--
Sheng Jiang
Microsoft MVP in VC++
"Anthony Paul" <an**********@gmail.comwrote in message
news:11**********************@o11g2000prd.googlegr oups.com...

让我们说我想要一个支持Min / Max的通用类型

属性，如果需要可以是double或整数甚至是datetime，

灵活的东西。


所以我要创建以下通用接口：


*注意：实际上我实现了IComparable和IEquatable通用

接口和相关的覆盖方法，但我已经削减了一切

这个例子的最低限度。


公共接口IMinMax< T>

{

T Min { get;}

T Max {get;}

}


和以下通用结构：


public struct MinMax< T：IMinMax< T>

{

private readonly T min;

private readonly T max ;


public T Min

{

get

{

返回分钟;

}

}


public T Max

{

get

{

返回最大值;

}

}


公共MinMax（T min，T max）

{

this.min = min;

this.max = max;

}


}


现在这里有一些代码可以使用它：

IMinMax< intintMinMax = new MinMax< int>（ 0,100）; //百分比范围

IMinMax< ddateMinMax = new MinMax< DateTime>（new DateTime（1973,10，

4），DateTime.Now）; //日期范围


好​​的，所以这就是问题......如果我有以下

程序怎么办？


public void DoSomething（object o）

{

IMinMax< mm =（IMinMax<>）o; //这个不行吗


//用mm.Min和mm.Max做点什么

}


我想按如下方式调用该程序：


DoSomething（intMinMax）;

DoSomething（dateMinMax）;


我们如何与Min和Max做点什么？显然，代码中缺少了很多肉，而且我为了这个新闻组的目的而将其简化为非常简单的

所以请不要

问我为什么要这样做...这会以一种或另一种形式出现所有

时间。


我猜真实问题是......一旦你将一个通用界面

投射到一个对象上，你如何在run-

时间内提取它的信息呢？在我的情况下，我碰巧在运行时知道类型，但是修改后的方法后面的

仍然不起作用：


public void DoSomething（Type t，对象o）

{

IMinMax< tmm =（IMinMax< t>）o; //仍然无法工作


//用mm.Min和mm.Max做点什么

}


问候！


Anthony

Let''s say that I would like a generic type that supports Min/Max
properties and can be double or integer or even datetime if need be,
something flexible.

So I go about creating the following generic interface :

*note : in reality I implement the IComparable and IEquatable generic
interfaces and associated overriden methods, but I''ve cut everything
down to the bare minimum for this example.

public interface IMinMax<T>
{
T Min{get;}
T Max{get;}
}

and the following generic struct :

public struct MinMax<T: IMinMax<T>
{
private readonly T min;
private readonly T max;

public T Min
{
get
{
return min;
}
}

public T Max
{
get
{
return max;
}
}

public MinMax(T min, T max)
{
this.min = min;
this.max = max;
}

}
Now here''s some code to use it :

IMinMax<intintMinMax = new MinMax<int>(0, 100); // percentage range
IMinMax<ddateMinMax = new MinMax<DateTime>(new DateTime(1973, 10,
4), DateTime.Now); // date range
Okay, so here''s the problem... what if I have the following
procedure :

public void DoSomething(object o)
{
IMinMax<mm = (IMinMax<>) o; // this doesn''t work

// do something with mm.Min and mm.Max here
}

and I want to call the procedure as follows :

DoSomething(intMinMax);
DoSomething(dateMinMax);
How do we go about doing something with Min and Max? Obviously there''s
a lot of meat missing in the code and I simplified it quite
unrealistically for the purpose of this newsgroup so please no
questions as to why I would want to do it... this comes up all the
time in one form or another.

I guess the real question is... once you''ve cast a generic interface
to an object, how do you go about extracting its information at run-
time? In my case I happen to know the type at runtime but the
following modified method still doesn''t work :

public void DoSomething(Type t, object o)
{
IMinMax<tmm = (IMinMax<t>) o; // still doesn''t work

// do something with mm.Min and mm.Max here
}
Regards!

Anthony

盛江[MVP]< sh *********@hotmail.com.discusswrote：

Sheng Jiang[MVP] <sh*********@hotmail.com.discusswrote:

您的结构（或值类型）已装箱且类型信息似乎丢失了

转换为对象时..

Your struct (or value type) is boxed and the type information seems lost
when it is converted to object..

不，当盒装信息时，类型信息肯定不会丢失。试试

取消装箱错误的类型 - 你会很快发现的。


-

Jon Skeet - < sk *** @ pobox.com>
http：// www .pobox.com / ~silet 博客： http：//www.msmvps .com / jon.skeet

如果回复小组，请不要给我发邮件

No, type information is certainly *not* lost when it''s boxed. Just try
unboxing something to the wrong type - you''ll find out soon enough.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

看来他没有指定泛型的类型

这个程序运行正常

static void Main（string [] args）

{

IMinMax< intintMinMax = new MinMax< int>（0,100）; //百分比

范围

IMinMax< DateTimedateMinMax = new MinMax< DateTime>（新

DateTime（1973,10，

4），DateTime.Now）; //日期范围

DoSomething< int>（intMinMax）;

DoSomething< DateTime>（dateMinMax）;


}

public static void DoSomething< T>（对象o）

{

IMinMax< Tmm =（IMinMax< T>）o;


//用mm.Min和mm.Max做点什么

}


-

Sheng Jiang

VC ++中的Microsoft MVP

" Jon Skeet [C＃MVP]" < sk *** @ pobox.com写了留言

新闻：MP ********************* @ msnews.microsoft.com 。 ..

It seems he did not specify the type for the generics
this program runs fine
static void Main(string[] args)
{
IMinMax<intintMinMax = new MinMax<int>(0, 100); // percentage
range
IMinMax<DateTimedateMinMax = new MinMax<DateTime>(new
DateTime(1973, 10,
4), DateTime.Now); // date range
DoSomething<int>(intMinMax);
DoSomething<DateTime>(dateMinMax);

}
public static void DoSomething<T>(object o)
{
IMinMax<Tmm = (IMinMax<T>) o;

// do something with mm.Min and mm.Max here
}

--
Sheng Jiang
Microsoft MVP in VC++
"Jon Skeet [C# MVP]" <sk***@pobox.comwrote in message
news:MP*********************@msnews.microsoft.com. ..

盛江[MVP]< sh ********* @ hotmail.com.discusswrote：

Sheng Jiang[MVP] <sh*********@hotmail.com.discusswrote:

您的结构（或值类型）被装箱，类型信息似乎丢失

转换为对象时..

Your struct (or value type) is boxed and the type information seems lost
when it is converted to object..

不，当盒装信息时，类型信息肯定不会丢失。试试

取消装箱错误的类型 - 你会很快发现的。


-

Jon Skeet - < sk *** @ pobox.com>
http：// www .pobox.com / ~silet 博客： http：//www.msmvps .com / jon.skeet

如果回复小组，请不要给我发邮件

No, type information is certainly *not* lost when it''s boxed. Just try
unboxing something to the wrong type - you''ll find out soon enough.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

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