C# event cannot call anonymous method with the correct argument value

Question

I have this code:

for (int i = 0; i < 7; ++i)
    Roption.DropDownItems.Add(string.Concat("Item &", i), null, delegate { Reset(i); });

where Reset() is called when the dropdown item is clicked.

The problem is that no matter which dropdown item is clicked, the argument passed to Reset is 7 (the value of i after the loop terminates), not the value of i when the Roption.DropDownItems.Add function is called. What causes this behavior and how can it be fixed? (I don't really want to hard code 0 through 6 in seven otherwise identical statements).

Make a copy of variable `i` like this `i1 = i` and pass `i1` to reset method instead... http://stackoverflow.com/questions/271440/captured-variable-in-a-loop-in-c-sharp — M.kazem Akhgary, Jun 19 '16 at 21:53

Snoop · Accepted Answer · 2016-06-20T00:31:35.330

Your problem here is that when you are creating the delegates in a loop, all objects will be passed by reference. This means that regardless of whether they are value-type or reference-type objects, they will still get passed by reference.

So what does this mean for your code? Well, as the loop iterates through, all of the Reset method calls that have a copy of i have a reference to the same one. So, as the value of i increases, so does the value for every single reference.

Closures Explained

C# event cannot call anonymous method with the correct argument value

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