List<object>.RemoveAll - 如何创建适当的谓词 [英] List<object>.RemoveAll - How to create an appropriate Predicate

问题描述

这是一个菜鸟问题 - 我对 C# 和泛型还很陌生，对谓词、委托和 lambda 表达式完全陌生...

This is a bit of noob question - I'm still fairly new to C# and generics and completely new to predicates, delegates and lambda expressions...

我有一个查询"类，其中包含另一个名为车辆"的类的通用列表.我正在构建代码以从父查询中添加/编辑/删除车辆.目前，我正在专门研究删除.

I have a class 'Enquiries' which contains a generic list of another class called 'Vehicles'. I'm building up the code to add/edit/delete Vehicles from the parent Enquiry. And at the moment, I'm specifically looking at deletions.

从我目前阅读的内容来看，我似乎可以使用 Vehicles.RemoveAll() 来删除具有特定 VehicleID 的项目或具有特定 EnquiryID 的所有项目.我的问题是理解如何提供 .RemoveAll 正确的谓词 - 我看到的示例过于简单(或者由于我缺乏谓词、委托和 lambda 表达式的知识，我可能过于简单了).

From what I've read so far, it appears that I can use Vehicles.RemoveAll() to delete an item with a particular VehicleID or all items with a particular EnquiryID. My problem is understanding how to feed .RemoveAll the right predicate - the examples I have seen are too simplistic (or perhaps I am too simplistic given my lack of knowledge of predicates, delegates and lambda expressions).

所以，如果我有一个 List<Of Vehicle>车辆，其中每个车辆都有一个 EnquiryID，我将如何使用 Vehicles.RemoveAll() 删除给定 EnquiryID 的所有车辆?

So if I had a List<Of Vehicle> Vehicles where each Vehicle had an EnquiryID, how would I use Vehicles.RemoveAll() to remove all vehicles for a given EnquiryID?

我知道有几种方法可以解决这个问题，所以我很想听听方法之间的区别 - 尽管我需要让某些东西发挥作用，但这也是一种学习练习.

I understand there are several approaches to this so I'd be keen to hear the differences between approaches - as much as I need to get something working, this is also a learning exercise.

作为补充问题，通用列表是这些对象的最佳存储库吗?我的第一个倾向是收藏，但似乎我已经过时了.当然泛型似乎是首选，但我对其他替代方案很好奇.

As an supplementary question, is a Generic list the best repository for these objects? My first inclination was towards a Collection, but it appears I am out of date. Certainly Generics seem to be preferred, but I'm curious as to other alternatives.

推荐答案

RemoveAll() 方法接受 Predicate 委托(直到这里没有新内容).谓词指向一个简单地返回真或假的方法.当然，RemoveAll 将从集合中删除所有返回 True 且应用了谓词的 T 实例.

The RemoveAll() methods accept a Predicate<T> delegate (until here nothing new). A predicate points to a method that simply returns true or false. Of course, the RemoveAll will remove from the collection all the T instances that return True with the predicate applied.

C# 3.0 允许开发人员使用多种方法将谓词传递给 RemoveAll 方法(而不仅仅是这个……).你可以使用:

C# 3.0 lets the developer use several methods to pass a predicate to the RemoveAll method (and not only this one…). You can use:

Lambda 表达式

vehicles.RemoveAll(vehicle => vehicle.EnquiryID == 123);

匿名方法

vehicles.RemoveAll(delegate(Vehicle v) {
  return v.EnquiryID == 123;
});

普通方法

vehicles.RemoveAll(VehicleCustomPredicate);
private static bool
VehicleCustomPredicate (Vehicle v) {
    return v.EnquiryID == 123; 
}

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