Question

Well, I need to check if there exists duplicate items inside listview on my app, but… I don’t know how.

The way to detect this is by checking the field “Tag”, if they are the same, then delete the item.

Answer 1

A good way to find duplicates is to use a temporary hashset. This gives you an O(n) O(n log n) algorithm (see Rick Sladkeys comments) to detect duplicates. Example:

var tags = new HashSet<string>();
var duplicates = new List<Item>();

foreach(Item item in listView.Items)
{
    // HashSet.Add() returns false if it already contains the key.
    if(!tags.Add(item.Tag) 
        duplicates.Add(item);
}

[Remove duplicates here]