从 IList 中查找和删除

Question

I have a IList of users

private IList<User> _Players

I have a method to remove a specific user from the list

public virtual void RemovePlayer(User User)
{
    int index=_Players.Select(T=>T.ID).ToList().IndexOf(User.ID);
    _Players.RemoveAt(index);
}

I would like to know if there is a simpler way to remove a user from this list

Answer 1

How about this? Use this if your parameter User is not part of _Players .

 _Players.Remove(_Players.SingleOrDefault(x => x.ID == User.ID));

The SingleOrDefault() ensures that if the match is not found, that null is returned. When trying to remove null, no err occurs or is thrown.

Answer 2

If the User objects you use are held within the _ Players list (same object references) you can just do

_Players.Remove(user);

Otherwise if only the id matches you can do:

_Players.RemoveAll( p => p.ID == user.ID);

Answer 3

There are two scenarios, the user variable that you are passing to RemovePlayer

1. is actually contained in your list
2. has the same ID value, but is not the same object.

From your code sample it is impossible to say.

For the first case just call _Players.Remove(user) . For the second case implement the System.IEquatable<User> interface on User to define a default EqualityComparer<User> and then again call _Players.Remove(user) . This second scenario works in both cases.

Answer 4

Depends, if you have implemented IEquatable on your user to compare by the ID , then you could simply do _Players.Remove(user) .

Otherwise:

var doomed = _Players.FirstOrDefault(p => p.ID == user.ID);
if (doomed != null)
   _Players.Remove(doomed);

Answer 5

Only in case if you have List<T> :

All the mentioned algorithms with SingleOrDefault() / FirstOrDefault() require two traversals among list:

1) first one to find an item by criteria

2) second one to find index of item by its value found in step #1

It's a bit more efficient to do like this instead:

int index = list.FindIndex(i => criteria);

if (index >= 0)
  list.RemoveAt(index);

Answer 6

Just wanted to do the same, but couldn't find a standard way.
Decided to go code it myself for my int lists. This little one won't do double-pass on the list!
You can replace int with object to work with classes.

public static bool FindAndRemoveFirst(this ICollection<int> list, Func<int, bool> predicate)
{
    var en = list.GetEnumerator();
    while (en.MoveNext())
    {
        if (predicate(en.Current))
        {
            list.Remove(en.Current);
            return true;
        }
    }
    return false;
}