vb.net LINQ-to-List 和 IEnumerable 问题
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1449291/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
LINQ-to-List and IEnumerable issues
提问by Todd Main
I am querying an HTML file with LINQ-to-XML. It looks something like this:
我正在使用 LINQ-to-XML 查询 HTML 文件。它看起来像这样：
<html>
<body>
<div class="Players">
<div class="role">Goalies</div>
<div class="name">John Smith</div>
<div class="name">Shawn Xie</div>
<div class="role">Right Wings</div>
<div class="name">Hyman Davis</div>
<div class="name">Carl Yuns</div>
<div class="name">Wayne Gortonia</div>
<div class="role">Centers</div>
<div class="name">Lutz Gaspy</div>
<div class="name">John Jacobs</div>
</div>
</body>
</html>
What I'm trying to do is create a list of these folks like in a list of a structure called Players:
我想要做的是创建一个这些人的列表，就像在一个名为 Players 的结构列表中一样：
Structure Players
Public Name As String
Public Position As String
End Structure
But I've quickly found out I don't really know what I'm doing when it comes to LINQ.
但我很快发现，当谈到 LINQ 时，我真的不知道我在做什么。
I've got this far in my queries:
我在我的查询中已经走了这么远：
Dim goalieList = From d In player.Elements _
Where d.Value = "Goalies" _
Select From g In d.ElementsAfterSelf _
Take While (g.@class <> "role") _
Select New Players With {.Position = "Goalie", _
.Name = g.Value}
Dim centersList = From d In player.Elements _
Where d.Value = "Centers" _
Select From g In d.ElementsAfterSelf _
Take While (g.@class <> "role") _
Select New Players With {.Position = "Centers", _
.Name = g.Value}
Which gets me down to the players by position, but then I can't do much with this afterwards the result type is System.Collections.Generic.IEnumerable(Of System.Collections.Generic.IEnumerable(Of Player))
这让我按位置找到了球员，但是之后我无法做太多事情，结果类型是 System.Collections.Generic.IEnumerable(Of System.Collections.Generic.IEnumerable(Of Player))
What I want to do is add these two results to a new list, like:
我想要做的是将这两个结果添加到一个新列表中，例如：
Dim playersList As List(Of Players) = Nothing
playersList.AddRange(centersList)
playersList.AddRange(goalieList)
So that I can then query the list and use it. But it kicks the error:
这样我就可以查询列表并使用它。但它会引发错误：
Unable to cast object of type 'WhereSelectEnumerableIterator
2[System.Xml.Linq.XElement,System.Collections.Generic.IEnumerable1[Players]]' to type 'System.Collections.Generic.IEnumerable`1[Players]'
无法将“WhereSelectEnumerableIterator
2[System.Xml.Linq.XElement,System.Collections.Generic.IEnumerable1[Players]]”类型的对象转换为“System.Collections.Generic.IEnumerable`1[Players]”
As you can see, I may really have no idea how to work with all these objects/classes. Does anyone have any insight on what I may be doing wrong and how I can resolve it?
如您所见，我可能真的不知道如何处理所有这些对象/类。有没有人对我可能做错了什么以及我如何解决它有任何见解？
RESOLVED: The LINQ query needs to return a single IEnumerable, like this:
已解决：LINQ 查询需要返回单个 IEnumerable，如下所示：
Dim goalieList = From l In _
(From d In players.Elements _
Where d.Value = "Goalies" _
Select d.ElementsAfterSelf.TakeWhile(Function(f) f.@class <> "role")) _
Select New Players With {.Position = "Goalie", .Name = l.Value}
and then use goalieList.ToList
然后使用 goalieList.ToList
采纳答案by Alan
I fail at VB, but in C# you would call ToList() on the centersList and goalieList.
我在 VB 上失败了，但是在 C# 中，您会在中心列表和守门员列表上调用 ToList()。
So something like:
所以像：
playersList.AddRange(centersList.ToList())
playersList.AddRange(goalieList.ToList())
回答by Igor ostrovsky
Any chance that you have two Players classes? Otherwise, I don't see how you could possibly get that error message.
您是否有机会拥有两个 Players 课程？否则，我看不到您怎么可能收到该错误消息。
Looking into Reflector, WhereSelectEnumerableIterator implements IEnumerable, so the cast should succeed.
查看 Reflector，WhereSelectEnumerableIterator 实现了 IEnumerable，因此转换应该会成功。
