How to fire delete event for a Item of extended BindingList when a PropertyGrid delete this item?

Question

The problem is that, I use this extended BindingList

public class RemoveItemEventArgs : EventArgs
{
    public Object RemovedItem
    {
        get { return removedItem; }
    }
    private Object removedItem;

    public RemoveItemEventArgs(object removedItem)
    {
        this.removedItem = removedItem;
    }
}

public class MyBindingList<T> : BindingList<T>
{
    public event EventHandler<RemoveItemEventArgs> RemovingItem;
    protected virtual void OnRemovingItem(RemoveItemEventArgs args)
    {
        EventHandler<RemoveItemEventArgs> temp = RemovingItem;
        if (temp != null)
        {
            temp(this, args);
        }
    }

    protected override void RemoveItem(int index)
    {
        OnRemovingItem(new RemoveItemEventArgs(this[index]));
        base.RemoveItem(index);
    }

    public MyBindingList(IList<T> list)
        : base(list)
    {
    }

    public MyBindingList()
    {
    }
}

I create an instance of this extended class and then I try to edit it by using PropertyGrid. When I delete an item, it does not fire the delete event. But when I edit the instance using method RemoveAt(...) it works well.

1. What the source of the issue?
2. Which method does PropertyGrid use to delete an item?
3. How do I catch the deleted event when PropertyGrid deletes an item?

Example :

public class Answer
{
    public string Name { get; set; }
    public int Score { get; set; }
}

public class TestCollection
{
    public MyBindingList<Answer> Collection { get; set; }
    public TestCollection()
    {
        Collection = new MyBindingList<Answer>();
    }
}

public partial class Form1 : Form
{
    private TestCollection _list;

    public Form1()
    {
        InitializeComponent();

    }
    void ItemRemoved(object sender, RemoveItemEventArgs e)
    {
        MessageBox.Show(e.RemovedItem.ToString());
    }

    void ListChanged(object sender, ListChangedEventArgs e)
    {
        MessageBox.Show(e.ListChangedType.ToString());
    }


    private void Form1_Load(object sender, EventArgs e)
    {
        _list = new TestCollection();
        _list.Collection.RemovingItem += ItemRemoved;
        _list.Collection.ListChanged += ListChanged;

        Answer q = new Answer {Name = "Yes", Score = 1};
        _list.Collection.Add(q);
        q = new Answer { Name = "No", Score = 0 };
        _list.Collection.Add(q);

        propertyGrid.SelectedObject = _list;
    }
}

Why I have message of new item but I do not have message about deleted item when I edit the collection by PropertyGrid ?

Answer 1

What the source of the issue? Which method does PropertyGrid use to delete an item?

The source of issue is that the PropertyGrid invoked a standard collection editor for the BindingList editing. This editor does not use the Remove() method on collection items at all, but only the IList.Clear() method and the IList.Add() method for each item that exist in list after editing (You can pass the CollectionEditor.SetItems() method to the Reflector for more detail).