如何在C＃中销毁列表数组的元素（或缩短长度）

Question

I have the following list:

List<MyOwnList> mylist = new List<MyOwnList>();

mylist[0].Name = "Name0";
mylist[0].Class = "Class0";

mylist[1].Name = "Name1";
mylist[1].Class = "Class1";

mylist[2].Name = "Name2";
mylist[2].Class = "Class2";

mylist[3].Name = "Name3";
mylist[3].Class = "Class3";

mylist[4].Name = "Name4";
mylist[4].Class = "Class4";

I want to shorten the length or let's say destroy elements from position 3 and 4. I used the following code but it still prints "5" when I do mylist.Count

for(int i=0; i<mylist.Count; i++)
{
    if(i>2)
    {
        mylist[i] = null;
    }
}

I expect it to print "3" when I do mylist.Count

Answer 1

When you do this:

mylist[i] = null;

you're accually setting i th element to null, so you won't change size of your list. Basicaly you will have null there:

// true
bool elementIsNull = mylist[i] == null;

Use RemoveRange method:

// remove 2 elements starting at element with index 3
mylist.RemoveRange(3, 2);

Answer 2

it's depend how you define "destroy"

if you want to remove the element from the list and "destroy" the cell to reduce the list list you can use the RemoveAt - BUT it would shorten the list

if you want to "destroy" the element , GC will take care of that , as long no one is holding reference to this element

Answer 3

It really depends what you mean by Destroy .

If MyOwnList implements IDisposable , You would use:

int startIndex;
int numberOfItemsToRemove;

mylist.GetRange(startIndex, numberOfItemsToRemove).ForEach(m => m.Dispose()); 
mylist.RemoveRange(startIndex, numberOfItemsToRemove);

Otherwise:

int startIndex;
int numberOfItemsToRemove;
mylist.RemoveRange(startIndex, numberOfItemsToRemove);

Answer 4

You have to delete the items in reverse to avoid the indexoutofrange exception and please don't use a property of a list which is going to change in the condition of a loop

try this:

        List<MyOwnList> mylist = new List<MyOwnList>();

        mylist.Add(new MyOwnList { Name = "Name0", Class = "Class0" });
        mylist.Add(new MyOwnList { Name = "Name1", Class = "Class1" });
        mylist.Add(new MyOwnList { Name = "Name2", Class = "Class2" });
        mylist.Add(new MyOwnList { Name = "Name3", Class = "Class3" });
        mylist.Add(new MyOwnList { Name = "Name4", Class = "Class4" });

        mylist[0].Name = "Name0";
        mylist[0].Class = "Class0";

        mylist[1].Name = "Name1";
        mylist[1].Class = "Class1";

        mylist[2].Name = "Name2";
        mylist[2].Class = "Class2";

        mylist[3].Name = "Name3";
        mylist[3].Class = "Class3";

        mylist[4].Name = "Name4";
        mylist[4].Class = "Class4";


        int count = mylist.Count;

        for (int i = count - 1; i >= 0; i--)
        {

            if (i > 2)
            {
                mylist.RemoveAt(i);
                //mylist[i] = null;
            }
        }

        Console.WriteLine(mylist.Count);