how to use hash table to avoid duplicate entries in a listview when items are added to it?

what is the way to avoid the redundancy in the listview when the items are added to it.. im using winforms c#.net.. i mean how can i compare between the items in listview1 and items in listview2 so that while adding the items from one listview to another it could not enter the items that are already entered in the target listview.. im able to add items from one listview to othe开发者_JAVA百科r but it is adding auplicate items also what is the way to get rid of it..???

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You can think of something like:

Hashtable openWith = new Hashtable();
// Add some elements to the hash table. There are no 
// duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe");
openWith.Add("bmp", "paint.exe");
openWith.Add("dib", "paint.exe");
openWith.Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is 
// already in the hash table.
try
{
    openWith.Add("txt", "winword.exe");
}
catch
{
    Console.WriteLine("An element with Key = \"txt\" already exists.");
}
// ContainsKey can be used to test keys before inserting 
// them.
if (!openWith.ContainsKey("ht"))
{
    openWith.Add("ht", "hypertrm.exe");
    Console.WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]);
}

Now to meet the changes in the problem after edit, you can do it like this:

if(!ListView2.Items.Contains(myListItem))
{
    ListView2.Items.Add(myListItem);
}

You can also refer a similar problem in How to copy the selected items from one listview to another on button click in c#net?

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As suggested, hash table is a good way to deter such redundancy.

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A dictonary ... Any array.. a list all possible, just loop threw the items/subitems, add them to the "array" then loop threw the array to check it against the otehr list...

Here is a example i use to remove dups on a buttonclick, but you can easily change to the code to suit your needs.

I used the below to remove "Dups" in a listview on a button click, i am searching subitem you can edit code for your own use...

uses dictionary and a little easy "update" class i wrote.

private void removeDupBtn_Click(object sender, EventArgs e)
    {   

        Dictionary<string, string> dict = new Dictionary<string, string>();

        int num = 0;
        while (num <= listView1.Items.Count)
        {
            if (num == listView1.Items.Count)
            {
                break;
            }

            if (dict.ContainsKey(listView1.Items[num].SubItems[1].Text).Equals(false))
            {
                dict.Add(listView1.Items[num].SubItems[1].Text, ListView1.Items[num].SubItems[0].Text);
            }     

            num++;
        }

        updateList(dict, listView1);

    }

and using a little updateList() class...

   private void updateList(Dictionary<string, string> dict, ListView list)
    {
        #region Sort
        list.Items.Clear();

        string[] arrays = dict.Keys.ToArray();
        int num = 0;
        while (num <= dict.Count)
        {
            if (num == dict.Count)
            {
                break;
            }

            ListViewItem lvi;
            ListViewItem.ListViewSubItem lvsi;

            lvi = new ListViewItem();
            lvi.Text = dict[arrays[num]].ToString();
            lvi.ImageIndex = 0;
            lvi.Tag = dict[arrays[num]].ToString();

            lvsi = new ListViewItem.ListViewSubItem();
            lvsi.Text = arrays[num];
            lvi.SubItems.Add(lvsi);

            list.Items.Add(lvi);

            list.EndUpdate();

            num++;
        }
        #endregion
    }

Good luck!