Question

I am running into an issue and not really sure what is going on, hopefully someone can help!

I am gathering entries from a database and placing them in a list collection, I am using this list collection to populate a dictionary of “active” things, I am using the list as a template and the “active” entry items are all that will be manipulated until an “active” thing is removed and a new instance of the “active” thing is inserted into the dictionary from the list collection. The issue I am seeing is that the items in the list collection are being updated as well as the dictionary items.

This is a problem for me at at least. I am probably doing something horribly wrong hopefully someone can provide a better solution.

For example:

  public class DataEntry
    {
        public string DataOne { get; set; }
        public int DataTwo { get; set; }

    }

public static List<DataEntry> dataCollection = new List<DataEntry>();
public static Dictionary<int, DataEntry> ActiveList = new Dictionary<int, DataEntry>();
private static int activeIndex = 0;

public static void LoadListFromDB()
{

    dataCollection.Add(new DataEntry() { DataOne = "Lakedoo", DataTwo = 25 });


    foreach (DataEntry de in dataCollection)
    {
        ActiveList.Add(activeIndex++, de);
    }


    for (int i = 0; i < 5; i++)
    {
        ActiveList[0].DataTwo -= 2;
    }

    if (ActiveList[0].DataTwo < 25)
    {
        ActiveList.Remove(0);
    }

    foreach (DataEntry de in dataCollection)
    {
        ActiveList.Add(activeIndex++, de);
    }


}

Answer 1

Both your ActiveList and dataCollection are pointing to the same DataEntry instances.

You will have to make a Copy of the dataEntry before inserting it into the ActiveList. See Writing a copy constructor.

Then do:

foreach (DataEntry de in dataCollection)
{
    ActiveList.Add(activeIndex++, new DataEntry(de));
}