C#:更新列表< of>中的项目值. [英] C#: Update Item value in List<of T>

问题描述

我正在寻找一种方法来更新列表中的元素，而无需自己枚举.

I'm looking for a way to update an Element in a List without enumerating it on my own.

我得到了MyProjects类，其中包含一个名为Projects的列表.

I got the Class MyProjects which hold a List named Projects.

我想找到MyProjects.Projects-Class，其中Class1(名称)的成员属性等于值开销".

I want to find the MyProjects.Projects-Class, where a member property of Class1 (Name) equals the Value "Overhead".

有效方法:

foreach (Project prj in MyProjects.Projects) {
    if (prj.Name == "Overhead")
        prj.IsActive = true;
}; 

但是，我尝试使用Linq进行相同的操作，但是未能将其写为一行.这有可能吗?我不喜欢以上述方式进行迭代的原因是，我已经在该代码块中迭代了整个列表，并认为可能会有更漂亮的方法:)

I, however, try to do the same by using Linq, but failed in writing it as one line. Is this even possible? The reason why I don't like to iterate in the way above is that I already iterate the whole list in this codeblock and think, that there might be a more beautiful way :)

推荐答案

您不应尝试将所有内容简化为一行-就像可读性一样简短.在这种情况下，您可以使用:

You shouldn't try to get everything down to one line - just as brief as is readable. In this case, you can use:

foreach (var project in MyProjects.Projects.Where(p => p.Name == "Overhead"))
{
    project.IsActive = true;
}

那是在 querying 部分使用LINQ，这很合适，因为这就是LINQ的代表.我强烈敦促您不要以Mayank的答案那样对LINQ调用中的项进行突变.这很容易出错(如原始答案所证明的那样不起作用)，并且与LINQ的精神背道而驰.

That's using LINQ for the querying part, which is appropriate as that's what the Q of LINQ stands for. I'd strongly urge you not to mutate items within LINQ calls in the way that Mayank's answer does though. It's error-prone (as evidenced by the original answer not working) and against the spirit of LINQ.

这与IMO的可读性差不多.请注意，它的功能与原始代码完全相同-如果每一项可能都是您想要的，您就无法避免某事遍历列表中的每一项更新.

That's about as readable as it gets, IMO. It does exactly the same thing as the original code, mind you - you can't avoid something iterating over every item in the list, if every item might be one you want to update.

只是为了开怀大笑，如果您真的，真的想要用最少的代码来做到这一点，则可以使用:

Just for laughs, if you really, really wanted to do it in pretty minimal code, you could use:

// DON'T USE THIS!
MyProjects.Project.Count(p => p.Name == "Overhead" && (p.IsActive = true));

在这里，我们使用&&短路的事实来避免评估赋值(p.IsActive = true)，除非条件匹配.为属性分配bool值很方便，因为这意味着我们无需执行任何其他操作即可使它成为&&运算符的有效第二个操作数.我们使用Count()来完全评估结果，而无需创建任何其他列表等-并且我们使用带有谓词的版本来避免甚至不需要以前版本进行的Where调用. (LastOrDefault也可以.)但这都是一种可怕的滥用方式，绝不应该出现在任何真实的代码中.

Here we use the fact that && is short-circuiting to avoid evaluating the assignment (p.IsActive = true) unless the condition is matched. It's handy that we're assigning a bool value to a property, as that means we don't need to do anything else to make it a valid second operand for the && operator. We use Count() to fully evaluate the result without creating any additional lists etc - and we use the version with a predicate to avoid even needing a Where call, which a previous version did. (LastOrDefault would work too.) But it's all a horrible abuse, and should never appear in any real code.

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