blocks|key|1270996|text|需要记住的一件事是，LINQ语句使用deferred+execution。这意味着，直到您在foreach语句中迭代LINQ语句或调用myLine上的.ToList()方法，您的you语句才会实际执行。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1270997|对于您的示例，请尝试更改：|1270998|return+myLine;|code-block|syntax|javascript|1270999|至：|1271000|return+myLine.ToList();|1271001|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/bb669162.aspx^0|A|4|1A|7|1M|4|1V|6|23|9|I|I|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@$9|19|A|1A|1|1B]]|E|$]]|$1|F|3|G|5|6|7|1C|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1D|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1E|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1F|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

One thing to remember is that <code>LINQ</code> statements use <a href="http://msdn.microsoft.com/en-us/library/bb669162.aspx" rel="nofollow noreferrer">deferred execution</a>. What that means is that your <code>LINQ</code> statement doesn't actually execute until you either iterate over it in a <code>foreach</code> statement or you call the <code>.ToList()</code> method on <code>myLine</code>. 
For your example try changing:

<pre><code>return myLine;
</code></pre>

To:

<pre><code>return myLine.ToList();
</code></pre>

blocks|key|4028460|text|不能声明IEnumerable<AnonymousType>，因为该类型在生成时没有(已知)名称。因此，如果您想在函数声明中使用此类型，请将其设置为普通类型。或者只是修改您的查询以返回一个IENumerable<String>并坚持使用该类型。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4028461|或者使用下面的select语句返回IEnumerable<KeyValuePair<Int32,+String>>。|4028462|select+new+KeyValuePair<Int32,+String>(id,+m.Groups[2].Value)|code-block|syntax|javascript|4028463|entityMap^0|4|Q|2M|J|0|H|14|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

You cannot declare <code>IEnumerable&lt;AnonymousType&gt;</code> because the type has no (known) name at build time. So if you want to use this type in a function declaration, make it a normal type. Or just modify your query to return a <code>IENumerable&lt;String&gt;</code> and stick with that type.

Or return <code>IEnumerable&lt;KeyValuePair&lt;Int32, String&gt;&gt;</code> using the following select statement.

<pre><code>select new KeyValuePair&lt;Int32, String&gt;(id, m.Groups[2].Value)
</code></pre>

blocks|key|4028505|text|SearchItem上的方法签名指示该方法返回IEnumerable<string>，但在LINQ查询中声明的匿名类型不是string类型。如果你想保持相同的方法签名，你必须改变你的查询来只选择string。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4028506|return+myLine.Select(a+=>+a.Text);|code-block|syntax|javascript|4028507|如果坚持返回查询选择的数据，并且将return语句替换为，则可以返回IEnumerable<object>|4028508|return+myLine.Cast<object>();|4028509|然后，您可以使用反射来使用对象。|4028510|但实际上，如果您要在声明匿名类型的方法之外使用它，则应该定义一个类，并让该方法返回该类的IEnumerable。匿名类型很方便，但容易被滥用。|4028511|entityMap^0|0|A|N|J|1P|6|2P|6|0|0|H|6|Y|J|0|0|0|18|B|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1A|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|T|$]]

The method signature on <code>SearchItem</code> indicates that the method returns an <code>IEnumerable&lt;string&gt;</code> but the anonymous type declared in your LINQ query is not of type <code>string</code>. If you want to keep the same method signature, you have to change your query to only select <code>string</code>s. e.g.

<pre><code>return myLine.Select(a =&gt; a.Text);
</code></pre>

If you insist on returning the data selected by your query, you can return an <code>IEnumerable&lt;object&gt;</code> if you replace your <code>return</code> statement with

<pre><code>return myLine.Cast&lt;object&gt;();
</code></pre>

Then you can consume the objects using reflection.

But really, if your going to be consuming an anonymous type outside the method that it is declared in, you should define a class an have the method return an <code>IEnumerable</code> of that class. Anonymous types are convenience but they are subject to abuse.

blocks|key|4028568|text|当您正在执行的LINQ语句实际上返回一个IEnumerable时，您的函数正在尝试返回IEnumerable，其中T是编译时生成的类型。匿名类型并不总是匿名的，因为它们在代码编译后呈现出特定的、具体的类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4028569|但是，由于匿名类型在编译之前是短暂的，因此只能在创建它们的范围内使用。为了支持您提供的示例中的需求，我认为最简单的解决方案是创建一个简单的实体来存储查询结果：|4028570|public+class+SearchItemResult
{
++++public+string+Text+{+get;+set;+}
++++public+int+ItemId+{+get;+set;+}
++++public+string+Path+{+get;+set;+}
}

public+IEnumerable<SearchItemResult>+SearchItem(int[]+itemIds)
{
++++//+...
++++IEnumerable<SearchItemResult>+results+=+from+...+select+new+SearchItemResult+{+...+}
}|code-block|syntax|javascript|4028571|但是，如果您的最终目标不是检索某种类型的对象，并且您只对Path...then感兴趣，那么您仍然可以生成IEnumerable|4028572|IEnumerable<string>+lines+=+from+...+select+m.Groups[2].Value;|4028573|我希望这有助于澄清您对LINQ、可枚举和匿名类型的理解。:)|4028574|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Your function is trying to return IEnumerable&lt;string&gt;, when the LINQ statement you are executing is actually returning an IEnumerable&lt;T&gt; where T is a compile-time generated type. Anonymous types are not always anonymous, as they take on a specific, concrete type after the code is compiled. 

Anonymous types, however, since they are ephemeral until compiled, can only be used within the scope they are created in. To support your needs in the example you provided, I would say the simplest solution is to create a simple entity that stores the results of your query:

<pre><code>public class SearchItemResult
{
 public string Text { get; set; }
 public int ItemId { get; set; }
 public string Path { get; set; }
}

public IEnumerable&lt;SearchItemResult&gt; SearchItem(int[] itemIds)
{
 // ...
 IEnumerable&lt;SearchItemResult&gt; results = from ... select new SearchItemResult { ... }
}
</code></pre>

However, if your ultimate goal is not to retrieve some kind of object, and you are only interested in, say, the Path...then you can still generate an IEnumerable&lt;string&gt;:

<pre><code>IEnumerable&lt;string&gt; lines = from ... select m.Groups[2].Value;
</code></pre>

I hope that helps clarify your understanding of LINQ, enumerables, and anonymous types. :)

blocks|key|4028627|text|我不一定要推荐这个...它是类型系统的一种颠覆，但您可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4028628|1)更改您的方法签名以返回IEnumerable+(非泛型签名)|offset|length|style|CODE|4028629|2)添加cast+by+example帮助器：|4028630|public+static+class+Extensions{
++++public+static+IEnumerable<T>+CastByExample<T>(
++++++++++++this+IEnumerable+sequence,+
++++++++++++T+example)+where+T:+class
++++{
++++++++foreach+(Object+o+in+sequence)
++++++++++++yield+return+o+as+T;
++++}
}|code-block|syntax|javascript|4028631|3)然后调用方法，如下所示：|4028632|var+example+=+new+{+Text+=+"",+ItemId+=+0,+Path+=+""+};
foreach+(var+x+in+SeachItem(ids).CastByExample(example))
{
++++//+now+you+can+access+the+properties+of+x+
++++Console.WriteLine("{0},{1},{2}",+x.Text,+x.ItemId,+x.Path);
}|4028633|你就完了。|4028634|关键在于，如果您创建一个具有相同顺序的匿名类型，则类型和属性名在两个位置将被重用。了解了这一点，您可以使用泛型来避免反射。|4028635|希望这能帮助亚历克斯|4028636|entityMap|0|LINK|mutability|MUTABLE|url|http://blogs.msdn.com/alexj/archive/2007/11/22/t-castbyexample-t-object-o-t-example.aspx^0|0|D|B|0|4|F|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@$D|18|E|19|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|1A|8|@]|9|@$D|1B|E|1C|1|1D]]|A|$]]|$1|J|3|K|5|L|7|1E|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|1F|8|@]|9|@]|A|$]]|$1|Q|3|R|5|L|7|1G|8|@]|9|@]|A|$M|N]]|$1|S|3|T|5|6|7|1H|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1I|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1J|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1K|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]]]

I am not necessarily recommending this... 
It is a kind of subversion of the type system but you could do this:

1) change your method signature to return <code>IEnumerable</code> (the non generic one)

2) add a <a href="http://blogs.msdn.com/alexj/archive/2007/11/22/t-castbyexample-t-object-o-t-example.aspx" rel="noreferrer">cast by example</a> helper:

<pre><code>public static class Extensions{
 public static IEnumerable&lt;T&gt; CastByExample&lt;T&gt;(
 this IEnumerable sequence, 
 T example) where T: class
 {
 foreach (Object o in sequence)
 yield return o as T;
 }
}
</code></pre>

3) then call the method something like this:

<pre><code>var example = new { Text = "", ItemId = 0, Path = "" };
foreach (var x in SeachItem(ids).CastByExample(example))
{
 // now you can access the properties of x 
 Console.WriteLine("{0},{1},{2}", x.Text, x.ItemId, x.Path);
}
</code></pre>

And you are done.

The key to this is the fact that if you create an anonymous type with the same order, types and property names in two places the types will be reused. Knowing this you can use generics to avoid reflection.

Hope this helps
Alex

blocks|key|4028681|text|返回ValueTuple而不是匿名类。Ex+(使用“命名元组”)-|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4028682|(Text:+line,+ItemId:+id,+Path:+m.Groups[2].Value)|code-block|syntax|javascript|4028683|https://docs.microsoft.com/en-us/dotnet/csharp/tuples|4028684|而不是-|4028685|new+{+Text+=+line,+ItemId+=+id,+Path+=+m.Groups[2].Value+}|4028686|ValueTuple是C#版本7的一部分，最初是作为单独的NuGet包(System.ValueTuple)实现的。从.NET+4.7开始，它是一个内置类型。对于.NET核心，2.0之前的版本需要NuGet包，但它是内置的2.0版。|4028687|entityMap|0|LINK|mutability|MUTABLE|url^0|2|A|0|0|0|1H|0|0|0|0|0|A|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@]|D|@$9|14|A|15|1|16]]|E|$]]|$1|M|3|N|5|6|7|17|8|@]|D|@]|E|$]]|$1|O|3|P|5|H|7|18|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|L]]]]

Return a <code>ValueTuple</code> instead of an anonymous class. Ex (using &quot;named tuples&quot;)-
<pre><code>(Text: line, ItemId: id, Path: m.Groups[2].Value)
</code></pre>
<a href="https://docs.microsoft.com/en-us/dotnet/csharp/tuples" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/dotnet/csharp/tuples</a>
Instead of-
<pre><code>new { Text = line, ItemId = id, Path = m.Groups[2].Value }
</code></pre>
The <code>ValueTuple</code> is part of C# version 7 and was originally implemented as a separate NuGet package (System.ValueTuple). Starting with .NET 4.7 it is a built-in type. For .NET Core, versions prior to 2.0 required the NuGet package but it is built-in with version 2.0.

blocks|key|809917|text|此链接可能对最终在此处https://idreesdotnet.blogspot.com/2019/08/c-how-to-create-list-of-anonymous-type.html的其他人很有用|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|809918|第一个解决方案(共6个)非常简单|809919|1:首先创建匿名类型的对象，然后将其传递给数组并调用ToList()方法。|809920|+++var+o1+=+new+{+Id+=+1,+Name+=+"Foo"+};
+++var+o2+=+new+{+Id+=+2,+Name+=+"Bar"+};
+++var+list+=+new[]+{+o1,+o2+}.ToList();|code-block|syntax|javascript|809921|entityMap|0|LINK|mutability|MUTABLE|url|https://idreesdotnet.blogspot.com/2019/08/c-how-to-create-list-of-anonymous-type.html^0|B|2D|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|C|$K|L]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

this link could be useful for others who end up here
<a href="https://idreesdotnet.blogspot.com/2019/08/c-how-to-create-list-of-anonymous-type.html" rel="nofollow noreferrer">https://idreesdotnet.blogspot.com/2019/08/c-how-to-create-list-of-anonymous-type.html</a>
the first solution (of 6) is delightlfully simple
1: First create the object(s) of anonymous type and then pass it to an array and call ToList() method.
<pre><code> var o1 = new { Id = 1, Name = &quot;Foo&quot; };
 var o2 = new { Id = 2, Name = &quot;Bar&quot; };
 var list = new[] { o1, o2 }.ToList();
</code></pre>

This is my function:

<pre><code> private IEnumerable&lt;string&gt; SeachItem(int[] ItemIds)
 {
 using (var reader = File.OpenText(Application.StartupPath + @"\temp\A_A.tmp"))
 {
 var myLine = from line in ReadLines(reader)
 where line.Length &gt; 1
 let id = int.Parse(line.Split('\t')[1])
 where ItemIds.Contains(id)
 let m = Regex.Match(line, @"^\d+\t(\d+)\t.+?\t(item\\[^\t]+\.ddj)")
 where m.Success == true
 select new { Text = line, ItemId = id, Path = m.Groups[2].Value };
 return myLine;
 }
 }
</code></pre>

I get a compile error,because "myLine" is not a IEnumerable[string] and I don't know how to write IEnumerable[Anonymous]

"Cannot implicitly convert type 'System.Collections.Generic.IEnumerable[AnonymousType#1]' to 'System.Collections.Generic.IEnumerable[string]'"

LINQ: How to declare IEnumerable[AnonymousType]?

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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这是我的函数： private IEnumerable<string> SeachItem(int[] ItemIds) { using (var reader = File.OpenText(Application.StartupPath + @"\temp\A_A.tmp")) ...

问LINQ:如何声明IEnumerable[AnonymousType]？
EN

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问LINQ:如何声明IEnumerable[AnonymousType]？EN