为什么物体还活着？

Question

Just doing some practice and was breakpointing through this example. I found that the references of earlier created list members was still alive, why?

The anotherShoe and newShoe still had values that were assigned to their reference members however as you can see, the real objects was cleared. I know I can assign them null values but aren't they automatically nulled/garbage collected when their reference objects have been List<T>.Clear() ?

Thank you.

 List<Shoe> shoeCloset = new List<Shoe>();
            shoeCloset.Add(new Shoe() { styles = Styles.Sneakers, colour = "Red" });
            shoeCloset.Add(new Shoe() { styles = Styles.Sandals, colour = "Green" });
            shoeCloset.Add(new Shoe() { styles = Styles.Flipflops, colour = "Yellow"});
            shoeCloset.Add(new Shoe() { styles = Styles.Loafers, colour = "Brown" });
            shoeCloset.Add(new Shoe() { styles = Styles.Wingtips, colour = "Blue" });

            //int numberOfShoes = shoeCloset.Count;
            //foreach (Shoe shoe in shoeCloset)
            //{
            //    shoe.styles = Styles.Sneakers;
            //    shoe.colour = "White";
            //}

            shoeCloset.RemoveAt(3);

            Shoe newShoe = shoeCloset[2];
            Shoe anotherShoe = shoeCloset[1];
            anotherShoe.colour = "Grey";
            anotherShoe.colour = "Green";
            if (shoeCloset.Contains(anotherShoe))
            {
                Console.WriteLine("Contains another shoe");
            }

            shoeCloset.Clear();
            anotherShoe.ToString(); //<---this still contains values after shoeCloset has been cleared.
            newShoe.ToString();     //<---this still contains values after shoeCloset has been cleared.

Answer 1

Object instances are garbage collected when there is no possible way for any executing code to ever access them again. Since you're holding onto references to these two objects through two local variables that are still in scope, those objects are accessible, and thus not eligible for garbage collection.

The whole point of garbage collection is for you to not have to worry about it. You will never, ever (barring a few edge cases like unsafe code and weak references), try to access an object and find out that the object you're trying to access has been garbage collected.