c# - Determine selected tristate

Question

I have a treeview that displays a hierarchy of objects of type Company.

Company has (among others) a property Bool? Checked. I am using that value in the checkbox for each row. I would like the checkbox to (also) indicate if any childs has been selected, but Im not sure how to build the Getter for the Checked property.

I guess the problem is that the value does not only represent the current objects value, but also the combined value of the childs. Is it solvable or do I need to rethink?

This is the outcome I would like to get:

• Checked = True (if the item itself is checked)
• Checked = False (if the item itself is not checked AND all childs/grandchilds are not checked)
• Checked = Null (If the item itself is not checked and SOME childs/grandchilds are checked)
• Checked = Null (if the item itself is not checked and ALL childs/grandchilds are checked)

Class Company:

public class Company
{
    public Company()
    {
        this.childs = new List<Company>();
    }
    public int ID { get; set; }
    public string Title { get; set; }
    public List<Company> childs { get; set; }
    public int NrOfChilds { get { return childs.Count; } }
    public bool Checked {
        get { ??? }
        set { this.Checked = value; }
    }

Answer 1

Ok, so using nullable bool is an OLV requirement right?

But shouldn't something this work to achieve what you want?

class Entity {
    private bool? _CheckState;
    public List<Entity> ChildEntities { get; set; }

    public Entity() {
        _CheckState = false;
        ChildEntities = new List<Entity>();
    }

    public bool? CheckState {
        get {
            if (_CheckState == true) {
                return true;
            } else if (ChildEntities.All(child => child.CheckState == false)) {
                return false;
            } else {
                return null;
            }
        }
        set { _CheckState = value; }
    }
}