XElementDescendantsPropertyDescriptor.cs

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using System;
using System.Collections.Generic;
using System.Xml.Linq;
 
namespace MS.Internal.Xml.Linq.ComponentModel;
 
internal sealed class XElementDescendantsPropertyDescriptor : XPropertyDescriptor<XElement, IEnumerable<XElement>>
{
    private XDeferredAxis<XElement> _value;
 
    private XName _changeState;
 
    public XElementDescendantsPropertyDescriptor()
        : base("Descendants")
    {
    }
 
    public override object GetValue(object component)
    {
        return _value = new XDeferredAxis<XElement>((XElement e, XName n) => (!(n != null)) ? e.Descendants() : e.Descendants(n), component as XElement, null);
    }
 
    protected override void OnChanged(object sender, XObjectChangeEventArgs args)
    {
        if (_value == null)
        {
            return;
        }
        switch (args.ObjectChange)
        {
        case XObjectChange.Add:
        case XObjectChange.Remove:
            if (sender is XElement xElement2 && (_value.name == xElement2.Name || _value.name == null))
            {
                OnValueChanged(_value.element, EventArgs.Empty);
            }
            break;
        case XObjectChange.Name:
            if (sender is XElement xElement && _value.element != xElement && _value.name != null && (_value.name == xElement.Name || _value.name == _changeState))
            {
                _changeState = null;
                OnValueChanged(_value.element, EventArgs.Empty);
            }
            break;
        }
    }
 
    protected override void OnChanging(object sender, XObjectChangeEventArgs args)
    {
        if (_value != null)
        {
            XObjectChange objectChange = args.ObjectChange;
            if (objectChange == XObjectChange.Name)
            {
                _changeState = (sender as XElement)?.Name;
            }
        }
    }
}