Question

In my app I am writing data into a text file by converting a list into an array, later on I want to load it by converting it to the same list type and return it like that.

My code:

public abstract class PhoneBookCore
{
    protected string _group;

    public PhoneBookCore(string group)
    {
        this._group = group;
    }
}

public class Group : PhoneBookCore
{
    private List<PhoneBookCore> elements = new List<PhoneBookCore>();

    public List<PhoneBookCore> elementsList { 
         get { return new List<PhoneBookCore>(elements); } 
    }

    public Group(string name)
        : base(name)
    {
    }

class DataOptions
{
    public void Save(Group g)
    {
        string[] lines = g.elementsList.ConvertAll(p => p.ToString()).ToArray();
        File.WriteAllLines(path, lines);
    }

    public Group Load()
    {
        string[] buffer = File.ReadAllLines(path); // ----> How do I convert it back
                                                   //       to list of type group?

        return ;
    }
}  

How do I convert it back to list of type group?

Answer 1

Maybe (assuming that you want to pass the whole line to the Group-constructor)

List<Group> allgroups = File.ReadLines(path)   
    .Select(l => new Group(l))
    .ToList();

Note that I’ve used File.ReadLines which returns a streaming IEnumerable<string> instead of a string[], you can also read all into memory at once with File.ReadAllLines.

But why do you always create a new list in the elementsList property? Just return elements.

Edit If you want to create one group and set the elementsList from the lines, you need to provide the setter of the property first:

private List<PhoneBookCore> _elementsList = new List<PhoneBookCore>();
public List<PhoneBookCore> ElementsList
{ 
    get { return _elementsList; }
    set { _elementsList = value; }
}

Then you can initialize and set the group on this way:

Group g = new Group(path); // i have no idea
g.ElementsList = File.ReadLines(path)
    .Select(l => new PhoneBookCore(l))
    .ToList();

return g;