I have this code and do not understand why the out put is 22! I am afraid it should be 01! can anyone explain what happens? if the list store a method with a parameter, so the parameters should be 0 and 1 respectively!
List<Action> list = new List<Action>();
for (int i = 0; i < 2; i++)
{
list.Add(() => Console.Write(i));
}
foreach (var it in list)
{
it();
}
In your case Console.Write(i) will use value of i in the moment of action call. You firstly increment i in for loop then in second loop you call every action in the list. In the moment of call of every action i has value 2 - so, you get 22 as output.
To get expected result you should create local copy of i and use it:
for (int i = 0; i < 2; i++)
{
var temp = i;
list.Add(() => Console.Write(temp));
}
Addition to Roma Doskoch's anwser, another approach is to avoid for.
var list = Enumerable
.Range(0, 2)
.Select<int, Action>(i => () => Console.Write(i));
Closures capture variables, not values.
In your code, the closure captures the variable i, not whatever value happens to be stored in i on each iteration. When you invoke the action, the variable i has a value of 2 (because the loop has finished) and therefore 2 will be printed out twice.
In order to avoid this, as other answers already point out, you need to create a new variable every time around as a workaround to not being able to capture values; if you declare a new variable on every iteration then the result of capturing the variable is equivalent to capturing the value because you won't be changing it on the next iteration.
