Question

I need to make some changes so that I only retrieve one object at a time from my list instead of the entire list as I do now.

Right now ive got a private list in class B with a property returning the entire list basically making it public anyway and I want to change this.

The way class a looks(the ui class operating with the list) is, I enter some data validate it and send it to class B which in turn packages it into a list of objects based on the input.

Then class A needs to loop this list and add it to a listview for displaying it which looks like this at the moment:

    ListViewItem lvi = new ListViewItem();
        foreach ([Object] o in CLassB.getList())
        {
            lvi = new ListViewItem(o.property0);
            lvi.SubItems.Add(o.property1);
            lvi.SubItems.Add(o.property2);
            lvi.SubItems.Add(o.property3);
        }
    }

Object is my abstract class which controls how the different types of items are added and getList() is my method in class B returning the entire list.

The thing is these propertys are the common ones all classes share the there are some that arent, like a textbox that you enter specific text about the object and so on which is displayed like this:

    private void lvRegistered_ItemSelectionChanged(object sender, ListViewItemSelectionChangedEventArgs e)
    {
        if (Listview.SelectedItems.Count > 0)
        {
            foreach ([Object] ob in ClassB.getList())
            {
                if (Listview.SelectedItems[0].SubItems[0].Text == ob.id.ToString())
                {
                    TextBox.Clear();
                    TextBox.Text = ob.property4;
                }
            }
        }
    }

Now this all works great at the moment but now I have a returned list to operate on but I dont want to return the list making it public I want to return one object of the list based on an index number (yes the functionality will be exactly the same, I made a method returning the count of the private list so I can loop over it and return all). This is for practicing OOP for when I dont want to return everything.

How would this be done? All I can think of is making a new list, take an int as input and search my private list and find the index then add that to the other list and return that list, but I dont know if this is good practice or the best way to do it? Well I havent looked into how to “copy” one element over to next list either but might aswell check and see if theres a better way to do things?

Just get the feeling im “taking the long way around” this way

Answer 1

Not sure to understand, but how about a simple GetById method?

public class Foo
{
    public int Id { get; set; }

    public string Name { get; set; }
}

public class Test
{
    private List<Foo> list = new List<Foo>();

    public void Add(Foo foo)
    {
        this.list.Add(foo);
    }

    public Foo GetById(int id)
    {
        return this.list.FirstOrDefault(z => z.Id == id);
    }
}

....

Test test = new Test();
test.Add(new Foo { Id = 1, Name = "1" });
test.Add(new Foo { Id = 2, Name = "2" });
test.Add(new Foo { Id = 3, Name = "3" });

Foo foo2 = test.GetById(2);