CODEWITHSUNDEEP
c#arrayslist
Frank Martin
Frank Martin

Reputation: 3441

How to destroy elements (or shorten length) of list array in C#

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

Upvotes: 2

Views: 2078

Answers (4)

CodeMonkeyNo42
CodeMonkeyNo42

Reputation: 1

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);

Upvotes: 0

Zbigniew
Zbigniew

Reputation: 27604

When you do this:

mylist[i] = null;

you're accually setting ith 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);

Upvotes: 7

Avi Turner
Avi Turner

Reputation: 10456

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);

Upvotes: 0

Mzf
Mzf

Reputation: 5260

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

Upvotes: 0

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