Question

I can’t understand how to loop through an Action list. When I try it, I end up with the values being the same as the previous iteration.

Here’s the code (simplified example):

string[] strings = { "abc", "def", "ghi" };

var actions = new List<Action>();
foreach (string str in strings)
    actions.Add(new Action(() => { Trace.WriteLine(str); }));

foreach (var action in actions)
    action();

Output:

ghi
ghi
ghi

Why is it always selecting the final element in strings when it performs the action?
And how can I achieve the desired output which would be:

abc
def
ghi

Answer 1

Your action is a closure, therefore it accesses str itself, not a copy of str:

foreach (string str in strings)
{
    var copy = str; // this will do the job
    actions.Add(new Action(() => { Trace.WriteLine(copy); }));
}