简单方法*在LINQ查询中转换对象？不是*

本文介绍了简单方法*在LINQ查询中转换对象？不是*的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

灵感来自Albahari第8章的优秀C＃3.0 in a Nutshell

（这本书太棒了，你必须得到它，如果你必须买一个C＃

book）以及Jon Skeet的书的附录A，我将通过

一些LINQ查询。但是如何施展？（

见下面的内容，修改自别人的代码。

问题是查询''停止''（抛出一个演员例外）在3，并且

永远不会到达紫罗兰。

如何防止这种情况？

Pseudocode好的，只需要一个提示就可以了，但更多的当然是

更好。

RL

* PS - 通过简单的方式来投射我的意思是非常简短，可以在运行时工作，而不是像列出所有的CASE / SWITCH语句

可能提前，但是，我会得到所有答案。

//

List< objectwords = new List< object {" green"，" blue"，3，" violet"，

5};

//投放对象列表中键入''string''

//并投射每个字符串的前两个字母。

尝试

{

IEnumerable< strin gquery =

words.AsQueryable（）。Cast< string>（）。选择（str = str.Substring（0,2））;

foreach （查询中的字符串s）

Console.WriteLine（s）;

}

catch（ArgumentException ex）

{

Console.WriteLine（ex）;

}

catch（InvalidCastException ex2）

{

Console.WriteLine（" invalid cast！" + ex2）;

}

/ *此代码*应*生成以下输出，但

它突破了查询到达上面的''3'并抛出一个

InvalidCastException - 如何让它完成查询直到

结束？

gr

bl

vi

* /

RL

Inspired by Chapter 8 of Albahari''s excellent C#3.0 in a Nutshell
(this book is amazing, you must get it if you have to buy but one C#
book) as well as Appendix A of Jon Skeet''s book, I am going through
some LINQ queries. But how to cast? (

See the below, modified from somebody else''s code.

The problem is the query ''stops'' (throws a cast exception) at "3", and
never gets to "violet".

How to prevent this?

Pseudocode OK, just a hint is all I need, but more of course is
better.

RL

*PS--by "easy way to cast" I mean something very short, that can work
at runtime, not something like a CASE/SWITCH statement that lists all
possibilities ahead of time, but, I''ll take all answers.

//
List<objectwords = new List<object{ "green", "blue", 3, "violet",
5 };

// Cast the objects in the list to type ''string''
// and project the first two letters of each string.

try
{
IEnumerable<stringquery =
words.AsQueryable().Cast<string>().Select(str =str.Substring(0, 2));

foreach (string s in query)
Console.WriteLine(s);
}

catch (ArgumentException ex)
{
Console.WriteLine(ex);
}
catch (InvalidCastException ex2)
{
Console.WriteLine("invalid cast!" + ex2);
}

/* This code *should* produce the following output, but
it breaks out of the query when it gets to ''3'' above and throws an
InvalidCastException--how to get it to complete the query until the
end?

gr
bl
vi
*/

RL

RL

简单方法在LINQ查询中转换对象？不是

问题描述

推荐答案