按值从列表中删除项目

Question

I have a list of class objects and want to remove one item but it doesn´t work:

    class Person
    {
        public string name; 
        public Person(string s)
        {
            this.name = s;
        }
    }

    void ABC()
    {
        List<Person> newPersonList = new List<Person>();
        newPersonList.Add(new Person("A"));
        newPersonList.Add(new Person("B"));
        newPersonList.Add(new Person("C"));

        newPersonList.Remove(A);
        newPersonList.RemoveAt(1);
    }

RemoveAt(1) works and deletes item with the ID 1.

I think Remove(A) should delete the item with the value "A". But this is not working. Can someone explain why? And what is the right way to delete by value?

Answer 1

Easiest way to remove from list by element's property value:

newPersonList.RemoveAll(p => p.name == "A");

Nicer way would be to change Person like that:

class Person : IEquatable<Person>
{
    public readonly string Name;
    public Person(string name)
    {
        if (string.IsNullOrWhiteSpace(name))
            throw new ArgumentException("name");
        Name = name;
    }
    public static implicit operator string(Person p)
    {
        return p.Name;
    }
    public static implicit operator Person(string name)
    {
        return new Person(name);
    }
    public bool Equals(Person other)
    {
        return Name.Equals(other.Name);
    }
}

And then use it like that:

var newPersonList = new List<Person>
{
    new Person("A"),
    new Person("B"),
    new Person("C")
};
newPersonList.Remove("A");

Or even like that:

var newPersonList = new List<Person> { "A", "B", "C" };
newPersonList.Remove(new Person("A"));

Answer 2

So you want .net magically to guess that by "A" string you mean field name ? How is it supposed to derive it?

I would suggest you use a Dictionary if you want to operate things by their key (name in this case):

var dict = new Dictionary<string, Person>() {
   {"A", new Person("A")}
}

//and later

dict.Remove("A");

Answer 3

You have not declared A. To do newPersonList.Remove(A);

You have to declare an object Person A and add it to newPersonList

Person A = new Person("A");
newPersonList.Add(A);

Answer 4

Like other said "What is A ?". If it would be a variable that contains a Person that this will work.

void ABC()
{
    var A = new Person("A");
    var B = new Person("B");
    var C = new Person("C");
    List<Person> newPersonList = new List<Person>();
    newPersonList.Add(A);
    newPersonList.Add(B);
    newPersonList.Add(C);

    newPersonList.Remove(A);
}