blocks|key|1508141|text|在内部，yield语句被转换成作为实现IEnumerator接口类实现的状态机。它允许同时使用多个foreach语句遍历结果集。该类对您的代码不可见，它没有标记为可序列化。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1508142|所以，答案是否定的，这是不可能的。但是，您可以自己实现所需的枚举器，但它比yield需要更多的工作量。|1508143|entityMap^0|4|5|0|11|5|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

Internally, <code>yield</code> statement is transformed to state machine implemented as class that implements IEnumerator interface. It allows to iterate throught resultset using multiple foreach statements at the same time. That class is not visible to your code, it is not marked as serializable.

So, answer is no, it is not possible. But, you can implement desired enumerator by itself, but it requires more labor than <code>yield</code>.

blocks|key|1511337|text|只需确保在调用yield之前，将状态(即迭代器位置)保存在一个可序列化的字段(位置字段，或任何您称之为它的字段)中。然后，当类被反序列化时，只需使用location字段从您停止的地方继续。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1511338|但是，这将在什么时候有用呢？您是否计划在foreach循环中间序列化对象？如果你给你的类一个SetIteratorPosition()方法，它缺省为当前的位置，你可能会让它变得容易得多。这比在现有的定义良好的行为(收益)中增加副作用要明显得多，每个人都会明白IteratorPosition是可以保存的。|offset|length|style|CODE|1511339|注意:方法不能序列化。序列化数据，即属性和字段。|1511340|entityMap^0|0|1A|L|3L|G|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]|$D|P|E|Q|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|R|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|K|$]]

Just make sure that just before you call yield, that you save state (i.e., the iterators position) in a serializable field (the location field, or whatever you call it). Then, when the class is deserialized, simply continue where you left off, using the location field.

But, when will this be useful? Do you plan to serialize objects in the middle of a foreach loop? Maybe you make it a lot easier if you give you class a <code>SetIteratorPosition()</code> method, which defaults to the current position. It's clearer than adding side effects to existing well defined behavior (yield) and everyone'll understand that <code>IteratorPosition</code> can be saved.

Note: methods cannot be serialized. You serialize data, i.e., properties and fields.

blocks|key|765390|text|是。任何返回IEnumerable的方法都可以拥有自己的yield+return代码。如果您序列化了对象的内部状态，即它正在迭代什么以及它到达了多远，那么您可以在将来的某个时间重新加载该状态，并从您停止的地方继续枚举。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|765391|entityMap^0|S|C|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

Yes. Any method that returns an IEnumerable can have it's own code for <code>yield return</code> whatever you tell it to. If you serialize the internal state of your object as to what it was iterating and how far it got, then you can reload that state at some future time, and continue the enumeration right where you left off.

blocks|key|3901198|text|是的，你可以做到。注意事项。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|3901199|在这里可以找到一个使用yield序列化方法、反序列化和继续的示例：http://www.agilekiwi.com/dotnet/CountingDemo.cs+(Web+Archive+Link)。|CODE|3901200|一般来说，在不做额外工作的情况下尝试序列化将会失败。这是因为编译器生成的类没有使用Serializable属性进行标记。但是，您可以解决此问题。|3901201|我会注意到，它们没有被标记为可序列化的原因是因为它们是一个实现细节，并且在未来的版本中会受到破坏性更改的影响，因此您可能无法在较新的版本中对其进行反序列化。|3901202|与我在how+to+serialize+anonymous+delegates上问的一个问题有关，这个问题应该也适用于这个案例。|3901203|以下是“hack”的源代码：|3901204|//+Copyright+©+2007+John+M+Rusk+(http://www.agilekiwi.com)
//+
//+You+may+use+this+source+code+in+any+manner+you+wish,+subject+to+
//+the+following+conditions:
//
//+(a)+The+above+copyright+notice+and+this+permission+notice+shall+be
//+++++included+in+all+copies+or+substantial+portions+of+the+Software.
//
//+(b)+THE+SOFTWARE+IS+PROVIDED+"AS+IS",+WITHOUT+WARRANTY+OF+ANY+KIND,
//+++++EXPRESS+OR+IMPLIED,+INCLUDING+BUT+NOT+LIMITED+TO+THE+WARRANTIES
//+++++OF+MERCHANTABILITY,+FITNESS+FOR+A+PARTICULAR+PURPOSE+AND
//+++++NONINFRINGEMENT.+IN+NO+EVENT+SHALL+THE+AUTHORS+OR+COPYRIGHT
//+++++HOLDERS+BE+LIABLE+FOR+ANY+CLAIM,+DAMAGES+OR+OTHER+LIABILITY,
//+++++WHETHER+IN+AN+ACTION+OF+CONTRACT,+TORT+OR+OTHERWISE,+ARISING
//+++++FROM,+OUT+OF+OR+IN+CONNECTION+WITH+THE+SOFTWARE+OR+THE+USE+OR
//+++++OTHER+DEALINGS+IN+THE+SOFTWARE.

using+System;
using+System.Collections.Generic;
using+System.Diagnostics;
using+System.IO;
using+System.Reflection;
using+System.Runtime.Serialization;
using+System.Runtime.Serialization.Formatters.Soap;

namespace+AgileKiwi.PersistentIterator.Demo
{
++++///+<summary>
++++///+This+is+the+class+we+will+enumerate+over
++++///+</summary>
++++[Serializable]
++++public+class+SimpleEnumerable
++++{
++++++++public+IEnumerator<string>+Foo()
++++++++{
++++++++++++yield+return+"One";
++++++++++++yield+return+"Two";
++++++++++++yield+return+"Three";
++++++++}

++++++++#region+Here+is+a+more+advanced+example
++++++++//+This+shows+that+the+solution+even+works+for+iterators+which+call+other+iterators
++++++++//+See+SimpleFoo+below+for+a+simpler+example
++++++++public+IEnumerator<string>+AdvancedFoo()
++++++++{
++++++++++++yield+return+"One";
++++++++++++foreach+(string+s+in+Letters())
++++++++++++++++yield+return+"Two+"+%2B+s;
++++++++++++yield+return+"Three";
++++++++}

++++++++private+IEnumerable<string>+Letters()
++++++++{
++++++++++++yield+return+"a";
++++++++++++yield+return+"b";
++++++++++++yield+return+"c";
++++++++}
++++++++#endregion
++++}

++++///+<summary>
++++///+This+is+the+command-line+program+which+calls+the+iterator+and+serializes+the+state
++++///+</summary>
++++public+class+Program
++++{
++++++++public+static+void+Main()
++++++++{
++++++++++++//+Create/restore+the+iterator
++++++++++++IEnumerator<string>+e;
++++++++++++if+(File.Exists(StateFile))
++++++++++++++++e+=+LoadIterator();
++++++++++++else
++++++++++++++++e+=+(new+SimpleEnumerable()).Foo();+//+start+new+iterator

++++++++++++//+Move+to+next+item+and+display+it.
++++++++++++//+We+can't+use+foreach+here,+because+we+only+want+to+get+ONE+
++++++++++++//+result+at+a+time.
++++++++++++if+(e.MoveNext())
++++++++++++++++Console.WriteLine(e.Current);
++++++++++++else
++++++++++++++++Console.WriteLine("Finished.++Delete+the+state.xml+file+to+restart");

++++++++++++//+Save+the+iterator+state+back+to+the+file
++++++++++++SaveIterator(e);

++++++++++++//+Pause+if+running+from+the+IDE
++++++++++++if+(Debugger.IsAttached)
++++++++++++{
++++++++++++++++Console.Write("Press+any+key...");
++++++++++++++++Console.ReadKey();
++++++++++++}
++++++++}

++++++++static+string+StateFile
++++++++{
++++++++++++get+{
++++++++++++++++return+Path.Combine(
++++++++++++++++++++Path.GetDirectoryName(Assembly.GetEntryAssembly().Location),
++++++++++++++++++++"State.xml");
++++++++++++}
++++++++}

++++++++static+IEnumerator<string>+LoadIterator()
++++++++{
++++++++++++using+(FileStream+stream+=+new+FileStream(StateFile,+FileMode.Open))
++++++++++++{
++++++++++++++++ISurrogateSelector+selector+=+new+EnumerationSurrogateSelector();
++++++++++++++++IFormatter+f+=+new+SoapFormatter(selector,+new+StreamingContext());
++++++++++++++++return+(IEnumerator<string>)f.Deserialize(stream);
++++++++++++}
++++++++}

++++++++static+void+SaveIterator(IEnumerator<string>+e)
++++++++{
++++++++++++using+(FileStream+stream+=+new+FileStream(StateFile,+FileMode.Create))
++++++++++++{
++++++++++++++++ISurrogateSelector+selector+=+new+EnumerationSurrogateSelector();
++++++++++++++++IFormatter+f+=+new+SoapFormatter(selector,+new+StreamingContext());
++++++++++++++++f.Serialize(stream,+e);
++++++++++++}
++++++++++++#region+Note:+The+above+code+puts+the+name+of+the+compiler-generated+enumerator+class...
++++++++++++//+into+the+serialized+output.++Under+what+circumstances,+if+any,+might+a+recompile+result+in
++++++++++++//+a+different+class+name?++I+have+not+yet+investigated+what+the+answer+might+be.
++++++++++++//+I+suspect+MS+provide+no+guarantees+in+that+regard.
++++++++++++#endregion
++++++++}
++++}

++++#region+Helper+classes+to+serialize+iterator+state
++++//+See+http://msdn.microsoft.com/msdnmag/issues/02/09/net/#S3+
++++class+EnumerationSurrogateSelector+:+ISurrogateSelector
++++{
++++++++ISurrogateSelector+_next;

++++++++public+void+ChainSelector(ISurrogateSelector+selector)
++++++++{
++++++++++++_next+=+selector;
++++++++}

++++++++public+ISurrogateSelector+GetNextSelector()
++++++++{
++++++++++++return+_next;
++++++++}

++++++++public+ISerializationSurrogate+GetSurrogate(Type+type,+StreamingContext+context,+out+ISurrogateSelector+selector)
++++++++{
++++++++++++if+(typeof(System.Collections.IEnumerator).IsAssignableFrom(type))
++++++++++++{
++++++++++++++++selector+=+this;
++++++++++++++++return+new+EnumeratorSerializationSurrogate();
++++++++++++}
++++++++++++else
++++++++++++{
++++++++++++++++//todo:+check+this+section
++++++++++++++++if+(_next+==+null)
++++++++++++++++{
++++++++++++++++++++selector+=+null;
++++++++++++++++++++return+null;
++++++++++++++++}
++++++++++++++++else
++++++++++++++++{
++++++++++++++++++++return+_next.GetSurrogate(type,+context,+out+selector);
++++++++++++++++}
++++++++++++}
++++++++}
++++}

++++//+see+http://msdn.microsoft.com/msdnmag/issues/02/09/net/#S3
++++class+EnumeratorSerializationSurrogate+:+ISerializationSurrogate
++++{
++++++++public+void+GetObjectData(object+obj,+SerializationInfo+info,+StreamingContext+context)
++++++++{
++++++++++++foreach(FieldInfo+f+in+obj.GetType().GetFields(BindingFlags.Instance+%7C+BindingFlags.Public+%7C+BindingFlags.NonPublic))
++++++++++++++++info.AddValue(f.Name,+f.GetValue(obj));
++++++++}

++++++++public+object+SetObjectData(object+obj,+SerializationInfo+info,+StreamingContext+context,
++++++++++++++++++++++++++++++++++++ISurrogateSelector+selector)
++++++++{
++++++++++++foreach+(FieldInfo+f+in+obj.GetType().GetFields(BindingFlags.Instance+%7C+BindingFlags.Public+%7C+BindingFlags.NonPublic))
++++++++++++++++f.SetValue(obj,+info.GetValue(f.Name,+f.FieldType));
++++++++++++return+obj;
++++++++}
++++}
++++#endregion
}|code-block|syntax|javascript|3901205|entityMap|0|LINK|mutability|MUTABLE|url|http://www.agilekiwi.com/dotnet/CountingDemo.cs|1|http://web.archive.org/web/20120630161328/http://www.agilekiwi.com/dotnet/CountingDemo.cs|2|https://stackoverflow.com/questions/321827/serializing-anonymous-delegates-in-c^0|0|E|0|B|5|X|1B|0|2A|G|1|0|15|C|0|0|3|10|2|0|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1A|8|@$9|1B|A|1C|B|H]]|D|@$9|1D|A|1E|1|1F]|$9|1G|A|1H|1|1I]]|E|$]]|$1|I|3|J|5|6|7|1J|8|@$9|1K|A|1L|B|H]]|D|@]|E|$]]|$1|K|3|L|5|6|7|1M|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|1N|8|@]|D|@$9|1O|A|1P|1|1Q]]|E|$]]|$1|O|3|P|5|6|7|1R|8|@]|D|@]|E|$]]|$1|Q|3|R|5|S|7|1S|8|@]|D|@]|E|$T|U]]|$1|V|3|-4|5|6|7|1T|8|@]|D|@]|E|$]]]|W|$X|$5|Y|Z|10|E|$11|12]]|13|$5|Y|Z|10|E|$11|14]]|15|$5|Y|Z|10|E|$11|16]]]]

Yes, you can do this. With caveats.

An example of serializing a method with a <code>yield</code>, deserializing and continuing can be found here: <a href="http://www.agilekiwi.com/dotnet/CountingDemo.cs" rel="nofollow noreferrer">http://www.agilekiwi.com/dotnet/CountingDemo.cs</a> (<a href="http://web.archive.org/web/20120630161328/http://www.agilekiwi.com/dotnet/CountingDemo.cs" rel="nofollow noreferrer">Web Archive Link</a>).

In general, trying to serialize without doing some extra work will fail. This is bcause the compiler generated classes are not marked with the <code>Serializable</code> attribute. However, you can work around this.

I would note the reason that they aren't marked with serializable is because they are an implementation detail and subject to breaking changes in future versions, so you may not be able to deserialize it in a newer version.

Related to a question I asked on <a href="https://stackoverflow.com/questions/321827/serializing-anonymous-delegates-in-c">how to serialize anonymous delegates</a>, which should work for this case as well. 

Here's the source code of the "hack":

<pre><code>// Copyright © 2007 John M Rusk (http://www.agilekiwi.com)
// 
// You may use this source code in any manner you wish, subject to 
// the following conditions:
//
// (a) The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// (b) THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Reflection;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Soap;

namespace AgileKiwi.PersistentIterator.Demo
{
 /// &lt;summary&gt;
 /// This is the class we will enumerate over
 /// &lt;/summary&gt;
 [Serializable]
 public class SimpleEnumerable
 {
 public IEnumerator&lt;string&gt; Foo()
 {
 yield return "One";
 yield return "Two";
 yield return "Three";
 }

 #region Here is a more advanced example
 // This shows that the solution even works for iterators which call other iterators
 // See SimpleFoo below for a simpler example
 public IEnumerator&lt;string&gt; AdvancedFoo()
 {
 yield return "One";
 foreach (string s in Letters())
 yield return "Two " + s;
 yield return "Three";
 }

 private IEnumerable&lt;string&gt; Letters()
 {
 yield return "a";
 yield return "b";
 yield return "c";
 }
 #endregion
 }

 /// &lt;summary&gt;
 /// This is the command-line program which calls the iterator and serializes the state
 /// &lt;/summary&gt;
 public class Program
 {
 public static void Main()
 {
 // Create/restore the iterator
 IEnumerator&lt;string&gt; e;
 if (File.Exists(StateFile))
 e = LoadIterator();
 else
 e = (new SimpleEnumerable()).Foo(); // start new iterator

 // Move to next item and display it.
 // We can't use foreach here, because we only want to get ONE 
 // result at a time.
 if (e.MoveNext())
 Console.WriteLine(e.Current);
 else
 Console.WriteLine("Finished. Delete the state.xml file to restart");

 // Save the iterator state back to the file
 SaveIterator(e);

 // Pause if running from the IDE
 if (Debugger.IsAttached)
 {
 Console.Write("Press any key...");
 Console.ReadKey();
 }
 }

 static string StateFile
 {
 get {
 return Path.Combine(
 Path.GetDirectoryName(Assembly.GetEntryAssembly().Location),
 "State.xml");
 }
 }

 static IEnumerator&lt;string&gt; LoadIterator()
 {
 using (FileStream stream = new FileStream(StateFile, FileMode.Open))
 {
 ISurrogateSelector selector = new EnumerationSurrogateSelector();
 IFormatter f = new SoapFormatter(selector, new StreamingContext());
 return (IEnumerator&lt;string&gt;)f.Deserialize(stream);
 }
 }

 static void SaveIterator(IEnumerator&lt;string&gt; e)
 {
 using (FileStream stream = new FileStream(StateFile, FileMode.Create))
 {
 ISurrogateSelector selector = new EnumerationSurrogateSelector();
 IFormatter f = new SoapFormatter(selector, new StreamingContext());
 f.Serialize(stream, e);
 }
 #region Note: The above code puts the name of the compiler-generated enumerator class...
 // into the serialized output. Under what circumstances, if any, might a recompile result in
 // a different class name? I have not yet investigated what the answer might be.
 // I suspect MS provide no guarantees in that regard.
 #endregion
 }
 }

 #region Helper classes to serialize iterator state
 // See http://msdn.microsoft.com/msdnmag/issues/02/09/net/#S3 
 class EnumerationSurrogateSelector : ISurrogateSelector
 {
 ISurrogateSelector _next;

 public void ChainSelector(ISurrogateSelector selector)
 {
 _next = selector;
 }

 public ISurrogateSelector GetNextSelector()
 {
 return _next;
 }

 public ISerializationSurrogate GetSurrogate(Type type, StreamingContext context, out ISurrogateSelector selector)
 {
 if (typeof(System.Collections.IEnumerator).IsAssignableFrom(type))
 {
 selector = this;
 return new EnumeratorSerializationSurrogate();
 }
 else
 {
 //todo: check this section
 if (_next == null)
 {
 selector = null;
 return null;
 }
 else
 {
 return _next.GetSurrogate(type, context, out selector);
 }
 }
 }
 }

 // see http://msdn.microsoft.com/msdnmag/issues/02/09/net/#S3
 class EnumeratorSerializationSurrogate : ISerializationSurrogate
 {
 public void GetObjectData(object obj, SerializationInfo info, StreamingContext context)
 {
 foreach(FieldInfo f in obj.GetType().GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic))
 info.AddValue(f.Name, f.GetValue(obj));
 }

 public object SetObjectData(object obj, SerializationInfo info, StreamingContext context,
 ISurrogateSelector selector)
 {
 foreach (FieldInfo f in obj.GetType().GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic))
 f.SetValue(obj, info.GetValue(f.Name, f.FieldType));
 return obj;
 }
 }
 #endregion
}
</code></pre>

Is it possible to serialize a method containing <code>yield</code> statements (or a class that contains such a method) such that when you rehydrate the class, the internal state of the generated iterator is retained?

Serialization and the Yield statement

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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是否可以序列化包含yield语句的方法(或包含此类方法的类)，使得当您恢复该类的消重状态时，生成的迭代器的内部状态将被保留？

问序列化和Yield语句
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