blocks|key|4538570|text|使用LINQ：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4538571|Ireaders.Cast<ReaderInfo>().ToList();|code-block|syntax|javascript|4538572|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Using LINQ:

<pre><code>Ireaders.Cast&lt;ReaderInfo&gt;().ToList();
</code></pre>

blocks|key|4538584|text|您必须创建一个新列表，其中包含已抛出的项：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4538585|var+readers+=+Ireaders.Cast<ReaderInfo>().ToList();|code-block|syntax|javascript|4538586|或者，如果有可能有不兼容的IReaderInfo条目，并且您只希望得到结果中的实际ReaderInfo对象：|4538587|var+readers+=+Ireaders.OfType<ReaderInfo>().ToList();|4538588|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You have to create a new list with casted items:

<pre><code>var readers = Ireaders.Cast&lt;ReaderInfo&gt;().ToList();
</code></pre>

Or, if there is a possibility to have incompatible IReaderInfo entries and you only want the actual ReaderInfo objects in the result:

<pre><code>var readers = Ireaders.OfType&lt;ReaderInfo&gt;().ToList();
</code></pre>

blocks|key|4538598|text|通过使用Linq|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4538599|var+derivedList+=+Ireaders.Cast<ReaderInfo>();|code-block|syntax|javascript|4538600|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

By using Linq

<pre><code>var derivedList = Ireaders.Cast&lt;ReaderInfo&gt;();
</code></pre>

blocks|key|4538635|text|快速和非常脏的修复是只传递实际上是ReaderInfo的对象，使用OfType<>。如果任何对象实现了Cast<>而实际上不是ReaderInfo，那么使用ReaderInfo就会失败。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4538636|var+Ireaders+=+someobject.Getreaders();
var+readers=Ireaders.OfType<ReaderInfo>().ToList();
return+readers;|code-block|syntax|javascript|4538637|更好的解决方案是更改方法的签名以返回List<IReaderInfo>，或者更抽象的IList<IReaderInfo>。如果GetReaders返回一个接口列表，这意味着它可以返回实现该接口的任何对象。|style|CODE|4538638|为什么要抛弃他们中的一些？当所有实现相同的接口时，GetReaders为什么要决定使用哪些对象和丢弃哪些对象？|4538639|public+IList<IReaderInfo>+GetReaders
{
++++var+readers+=+new+List<ReaderInfo>();
++++var+Ireaders+=+someobject.Getreaders();//+Returns+the+list+of+IReaderInfo.
++++return+Ireaders;
}|4538640|例如，方法通常在打算返回不同类型(例如模拟对象或处理多个实现)时返回接口。通过返回List<ReaderInfo>，可以防止方法处理有效对象|4538641|更新|BOLD|4538642|版本控制是不应该将接口转换为具体类型的另一个非常强烈的原因。|4538643|在谷歌上搜索IReaderInfo时，我找到了几个页面，这些页面都提到了RFID阅读器。ReaderInfo返回读取器的功能，但是如何为新读取器公开新特性？|4538644|在不破坏兼容性的情况下，公开新特性的一个常见方法是引入一个实现旧接口IReaderInfo的新类，并通过新接口(如IReaderInfo2+)公开新特性。或者使用IReaderInfo2扩展现有的类。库可以这样做，因为客户端只能通过接口工作，而不是直接针对具体的类工作。|4538645|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/bb360913(v=vs.110).aspx)|1|https://msdn.microsoft.com/en-us/library/bb341406(v=vs.110).aspx^0|X|8|0|1F|6|1|0|0|I|H|16|I|1R|A|0|P|A|0|0|15|G|0|0|2|0|0|0|Y|B|1L|C|29|C|0^^$0|@$1|2|3|4|5|6|7|1B|8|@]|9|@$A|1C|B|1D|1|1E]|$A|1F|B|1G|1|1H]]|C|$]]|$1|D|3|E|5|F|7|1I|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1J|8|@$A|1K|B|1L|K|L]|$A|1M|B|1N|K|L]|$A|1O|B|1P|K|L]]|9|@]|C|$]]|$1|M|3|N|5|6|7|1Q|8|@$A|1R|B|1S|K|L]]|9|@]|C|$]]|$1|O|3|P|5|F|7|1T|8|@]|9|@]|C|$G|H]]|$1|Q|3|R|5|6|7|1U|8|@$A|1V|B|1W|K|L]]|9|@]|C|$]]|$1|S|3|T|5|6|7|1X|8|@$A|1Y|B|1Z|K|U]]|9|@]|C|$]]|$1|V|3|W|5|6|7|20|8|@]|9|@]|C|$]]|$1|X|3|Y|5|6|7|21|8|@]|9|@]|C|$]]|$1|Z|3|10|5|6|7|22|8|@$A|23|B|24|K|L]|$A|25|B|26|K|L]|$A|27|B|28|K|L]]|9|@]|C|$]]|$1|11|3|-4|5|6|7|29|8|@]|9|@]|C|$]]]|12|$13|$5|14|15|16|C|$17|18]]|19|$5|14|15|16|C|$17|1A]]]]

The quick&amp;very-dirty fix is to pass only the objects that actually are ReaderInfo, by using <a href="https://msdn.microsoft.com/en-us/library/bb360913(v=vs.110).aspx" rel="nofollow noreferrer">OfType&lt;></a>. Using <a href="https://msdn.microsoft.com/en-us/library/bb341406(v=vs.110).aspx" rel="nofollow noreferrer">Cast&lt;></a> will fail if any of the objects implements <code>IReaderInfo</code> without actually being a ReaderInfo

<pre><code>var Ireaders = someobject.Getreaders();
var readers=Ireaders.OfType&lt;ReaderInfo&gt;().ToList();
return readers;
</code></pre>

A better solution though would be to change the method's signature to return a <code>List&lt;IReaderInfo&gt;</code>, or the more abstract <code>IList&lt;IReaderInfo&gt;</code>. If <code>GetReaders</code> returns a list of interfaces it means it can return any object that implements the interface. 

Why discard some of them? Why should <code>GetReaders</code> decide which objects to use and which to discard when all implement the same interface?

<pre><code>public IList&lt;IReaderInfo&gt; GetReaders
{
 var readers = new List&lt;ReaderInfo&gt;();
 var Ireaders = someobject.Getreaders();// Returns the list of IReaderInfo.
 return Ireaders;
}
</code></pre>

For example, methods typically return interfaces when they do intend to return different types, eg mock objects, or handle multiple implementations. By returning <code>List&lt;ReaderInfo&gt;</code> you prevent your method from handling valid objects

UPDATE

Versioning is another very strong reason why one shouldn't cast interfaces to concrete types. 

Googling for IReaderInfo I found a couple of pages that refer to RFID readers. A ReaderInfo returns the capabilities of a reader, but how do you expose new features for a new reader?

A common way to expose new features without breaking compatibility is to introduce a new class that implement the old interface <code>IReaderInfo</code> and place expose new features through a new interface, eg <code>IReaderInfo2</code>. Or the existing class can be extended with <code>IReaderInfo2</code>. A library can do that because clients are expected to work only through the interfaces, not directly against the concrete classes.

I have an interface defined as 

<pre><code>public interface IReaderInfo
{
 string Displayname {get;}
}
</code></pre>

and a class that implements that interface

<pre><code>public class ReaderInfo : IReaderInfo
{
 string DisplayName {get;}
}
</code></pre>

I then created a function which return List 

<pre><code>public List&lt;ReaderInfo&gt; GetReaders
{
 var readers = new List&lt;ReaderInfo&gt;();
 var Ireaders = someobject.Getreaders();// Returns the list of IReaderInfo.
 // Now i would like cast Ireaders as readers and return.
}
</code></pre>

How do i cast it?

How do i convert a List<Interface> to List<Class> in c#

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个接口定义为public interface IReaderInfo{    string Displayname {get;}}以及实现该接口的类。public class ReaderInfo : IReaderInfo{    string DisplayName {get;}}然后我创建了一个返回列表的函...

问如何在List<Interface>中将List<Class>转换为c#
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