Why Do C# Loop Actions Capture the Same Variable, and How Can This Be Avoided?

The variables in the cycle capture

In C#, when defining the operation in the cycle, be sure to pay attention to the behavior of variable capture. By default, all operations capture the same variable, causing the output results to not meet the expected when calling.

Please consider the following example:

The expected output of this code is 0, 2, 4, 6, and 8. However, the actual output is five 10. This is because all operations quote the same captured variable

List<Action> actions = new List<Action>();

int variable = 0;
while (variable < 5)
{
    actions.Add(() => Console.WriteLine(variable * 2));
    ++variable;
}

foreach (var act in actions)
{
    act.Invoke();
}

, which is updated in the cycle. When calling, all operations have the same value 10.

variable In order to avoid this problem and ensure that each operation instance has its own capture variable, you need to copy the variable in the cycle:

Through the local copy of the variable, each operation captures its own unique value, so as to obtain the expected output 0, 2, 4, 6, 8.

while (variable < 5)
{
    int copy = variable;
    actions.Add(() => Console.WriteLine(copy * 2));
    ++variable;
}

The concept of this variable capture is critical to understanding the closure of C#. When defining operations within the cycle, be sure to consider the life cycle of the variable and its accessibility.

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