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listview duplicates

Posted on 2007-11-15
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Last Modified: 2013-12-17
how t o check for duplicates in a listview while adding it from a listbox
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Question by:kranthi4uonly
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8 Comments
 
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Expert Comment

by:Jaime Olivares
ID: 20291985
you can check by using ListView.public ListViewItem FindItemWithText() method.
It can search for a text in the first column, and there are other versions to check in other columns. I suggest to use the first one.
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Expert Comment

by:Jaime Olivares
ID: 20291990
Sorry, I meant:
you can check by using ListView.FindItemWithText() method.
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Expert Comment

by:longtruong
ID: 20295657
Hi,

You should use ListView.FindItemWithText() as suggested by jaime_olivares.  However, I am not sure if it is enough so I would like to give some additional information here.  If the item text is unique then this method is OK.  However, if the list has several items with the same text, this method always returns the first matched item.  To solve this situation, I suggest that when adding an item to the list, please do not forget associating a unique data to Tag attribute of each item and the Tag's value will be used as a key to search for a duplicate later.

Attached sample code is provided.

Hope it helps.

Long
public bool CheckDuplicate(int id)
{
    for (int i = 0; i < listView1.Items.Count; i++)
    {
        ListViewItem lvi = listView1.Items[i];
        if (lvi.Tag == (int)id)
        {
            return true;
        }
    }
    return false;
}
 
private void button1_Click(object sender, EventArgs e)
{
    //Check for duplicate
    if (CheckDuplicate(<your id here>) == false)
    {
        //Add new item to the list
        ListViewItem lvi = new ListViewItem();
        lvi.Text = "your item text here";
        lvi.Tag = "your id here";
        listView1.Items.Add(lvi);
    }
}

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Author Comment

by:kranthi4uonly
ID: 20296529
hi longtruong:
i dont have duplicates in listview
iam adding it from a listbox into list view
iam using the following code but why it is not working i cant understand


private void button1_Click(object sender, EventArgs e)
        {
           
            ListViewItem item = new ListViewItem(listBox1.SelectedItem.ToString());
            for (int i = 0; i < listView1.Items.Count; i++)
            {

                ListViewItem s =new ListViewItem(item.Text);
                if (listView1.Items[i].Text.Contains(s.Text))
                {
                    break ;
                }
                //else
                {

                    listView1.Items.AddRange(new ListViewItem[] { item });
                    break;


                }
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LVL 55

Expert Comment

by:Jaime Olivares
ID: 20296567
what about my suggestion?
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Author Comment

by:kranthi4uonly
ID: 20296650
yeah iam using ur code as like this but its saying object reference not set to an instance of object this works fien if their are duplicates
if not it gives exception as mentioned above
am i doing right
private void button1_Click(object sender, EventArgs e)
        {
           
            ListViewItem item = new ListViewItem(listBox1.SelectedItem.ToString());
            for (int i = 0; i < listView1.Items.Count; i++)
            {

                ListViewItem s =new ListViewItem(item.Text);
                ListViewItem j = listView1.FindItemWithText(s.Text);
                if (j.Text==s.Text && j!=null)
                {
                   
                    break ;
                }
                //else
                {
                    listView1.Items.AddRange(new ListViewItem[] { item });
                   
                    break;


                }
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LVL 55

Accepted Solution

by:
Jaime Olivares earned 500 total points
ID: 20296658
It is quiet simple:
private void button1_Click(object sender, EventArgs e)
{
    string text = listBox1.SelectedItem.ToString();
    if (listView1.FindItemWithText(text) == null)  // it is not duplicated
    {
         ListViewItem item = new ListViewItem(text);
         listView1.Items.Add(item);
    }
}

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Author Closing Comment

by:kranthi4uonly
ID: 31409411
excelent
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