Check an item on a list with Contains() method

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3.00/5 (2 votes)

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Hello I have a class named AddToGrid and a generic list.
AddToGrid class has properties such as ID, PART, QTY and WEIGHT.

While adding new items to the list from a gridview I want to check if the list has a same item with the same ID or not. if it doesnt have a matching ID I will add it to the list.
The code that I wrote;

for (int i = 0; i < gvParts.Rows.Count; i++)//loop the GridView Rows
        {
            AddToGrid mainList = new AddToGrid();
            mainList.ID = Convert.ToInt32(gvParts.Rows[i].Cells[1].Text);
            mainList.PART = gvParts.Rows[i].Cells[2].Text;
            mainList.QTY = Convert.ToInt32(gvParts.Rows[i].Cells[5].Text);
            string weightlbs = gvParts.Rows[i].Cells[3].Text;
            string[] weight = weightlbs.Split(' ');
            mainList.WEIGHT = Convert.ToDecimal(weight[0]);
            if (rmaPartLstDisp.Count == 0)
            {
                rmaPartLstDisp.Add(mainList);
            }
            else
            {                
                for (int j = 0; j < rmaPartLstDisp.Count; j++)
                {
                    if (!rmaPartLstDisp.Contains(mainList))
                    {
                        rmaPartLstDisp.Add(mainList);                        
                    }
                }
            }
      )

Inside the for loop on the if statement I need to have something like;

C#

for (int j = 0; j < rmaPartLstDisp.Count; j++)
               {
                   if (!rmaPartLstDisp.Contains(mainList.ID))
                   {
                       rmaPartLstDisp.Add(mainList);
                   }
               }

But it gives an error because of the invalid arguments.
Can someone help me find a proper way to check this? Thanks.

Posted 9-Feb-11 6:58am

Orcun Iyigun

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Comments

Orcun Iyigun 9-Feb-11 15:05pm

Thanks to all of you who answered my question and the suggestions that you gave.

4 solutions

Solution 2

You don't show the class AddToGrid, that's it. Most likely, your problem is resolved by type case, but the approach is wrong. Anyway, bad class, bad class name (should be noun, not a verb, there are good Microsoft naming conventions). Your problem is lack of generics.

You may need a generic class with item class being a generic parameter. List data can be presented as System.Collections.Generic interfaces and classes.

Also, Contains as a list method if slow operation of there are many items. For fast operation SystemCollections.Generic.Dictionary can be used.

—SA

Posted 9-Feb-11 7:16am

Sergey Alexandrovich Kryukov

Solution 3

1. you could use a dictionary

Dictionary<int, AddToGrid> mycontainer = new Dictionary<int, AddToGrid>();

if(!mycontainer.ContainsKey(myid))
//add it

otherwise the contains is a ref based search you can either create a icomparere or do something like

List<AddToGrid> mylist = new List<AddToGrid>();
if(mylist.FirstOrDefault<AddToGrid>( (item)=>item.Id==mynewId ) !=null)
    //add me

Posted 9-Feb-11 7:17am

cechode

Solution 4

Well let us see

C#

for (int j = 0; j < rmaPartLstDisp.Count; j++)
{
  if (!rmaPartLstDisp.Contains(mainList))
  {
     rmaPartLstDisp.Add(mainList);
  }
}

it appears that rmaPartLstDisp is a collection of AddToGrid . You need to implement your own Compare method in order for this to work. It is not that hard to do, see here[^] and here[^]

Posted 9-Feb-11 7:26am

Yusuf

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Henry Minute · Accepted Answer · 2011-02-09T07:13:00

Consider this part of your code:

C#

if (rmaPartLstDisp.Count == 0)
{
    rmaPartLstDisp.Add(mainList);
}
else
{
    for (int j = 0; j < rmaPartLstDisp.Count; j++)
    {
        if (!rmaPartLstDisp.Contains(mainList))
        {
            rmaPartLstDisp.Add(mainList);
        }
    }
}

First you check if the list count is zero. If it is then it cannot contain your mainList instance, so you add it. If the count is greater than zero you want to add it if it is not there.

So, regardless of the number of items in rmaPartLstDisp you want to add the mainList instance if it isn't there. Why bother doing all that checking then?

Simply replace all of that with:

C#

if (!rmaPartLstDisp.Contains(mainList))
{
    rmaPartLstDisp.Add(mainList);
}

If that was throwing an error before, it probably still will. So modify your question to add the new code and copy the exact error message.
[Edit added after OPs comment]

C#

if (rmaPartLstDisp.Count == 0)
{
    rmaPartLstDisp.Add(mainList);
}
else
{
    bool itemFound = false;
    foreach (AddToGrid atg in rmaPartLstDisp)
    {
        if (atg.ID == mainList.ID)
        {
            itemFound = true;
            break;
        }
    }
    if (!itemFound)
    {
      rmaPartLstDisp.Add(mainList);
    }
}

should do what you want.
[/Edit]