How do I update a single item in an ObservableCollection class?

How do I update a single item in an ObservableCollection class?

I know how to do an Add. And I know how to search the ObservableCollection one item at a time in a "for" loop (using Count as a representation of the amout of items) but how do I chage an existing item. If I do a "foreach" and find which item needs updating, how to I put that back into the ObservableCollection>

Here are Tim S's examples as extension methods on top of the Collection Class:

CS with FirstOrDefault

<!-- language: lang-cs -->

public static void ReplaceItem<T>(this Collection<T> col, Func<T, bool> match, T newItem)
{
    var oldItem = col.FirstOrDefault(i => match(i));
    var oldIndex = col.IndexOf(oldItem);
    col[oldIndex] = newItem;
}

CS with Indexed Loop

<!-- language: lang-cs -->

public static void ReplaceItem<T>(this Collection<T> col, Func<T, bool> match, T newItem)
{
    for (int i = 0; i <= col.Count - 1; i++)
    {
        if (match(col[i]))
        {
            col[i] = newItem;
            break;
        }
    }
}

Usage

Imagine you have this class setup

<!-- language: lang-cs -->

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}

You can call either of the following functions/implementations like this where the match parameter is used to identify the item you'd like to replace:

<!-- language: lang-cs -->

var people = new Collection<Person>
{
    new Person() { Id = 1, Name = "Kyle"},
    new Person() { Id = 2, Name = "Mit"}
};

people.ReplaceItem(x => x.Id == 2, new Person() { Id = 3, Name = "New Person" });

---

VB with Indexed Loop

<!-- language: lang-vb -->

<Extension()>
Public Sub ReplaceItem(Of T)(col As Collection(Of T), match As Func(Of T, Boolean), newItem As T)
    For i = 0 To col.Count - 1
        If match(col(i)) Then
            col(i) = newItem
            Exit For
        End If
    Next
End Sub  

VB with FirstOrDefault

<!-- language: lang-vb -->

<Extension()>
Public Sub ReplaceItem(Of T)(col As Collection(Of T), match As Func(Of T, Boolean), newItem As T)
    Dim oldItem = col.FirstOrDefault(Function(i) match(i))
    Dim oldIndex = col.IndexOf(oldItem)
    col(oldIndex) = newItem      
End Sub