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using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
namespace Xamarin.Forms
{
internal class AttachedCollection<T> : ObservableCollection<T>, ICollection<T>, IAttachedObject where T : BindableObject, IAttachedObject
{
readonly List<WeakReference> _associatedObjects = new List<WeakReference>();
public AttachedCollection()
{
}
public AttachedCollection(IEnumerable<T> collection) : base(collection)
{
}
public AttachedCollection(IList<T> list) : base(list)
{
}
public void AttachTo(BindableObject bindable)
{
if (bindable == null)
throw new ArgumentNullException("bindable");
OnAttachedTo(bindable);
}
public void DetachFrom(BindableObject bindable)
{
OnDetachingFrom(bindable);
}
protected override void ClearItems()
{
foreach (WeakReference weakbindable in _associatedObjects)
{
foreach (T item in this)
{
var bindable = weakbindable.Target as BindableObject;
if (bindable == null)
continue;
item.DetachFrom(bindable);
}
}
base.ClearItems();
}
protected override void InsertItem(int index, T item)
{
base.InsertItem(index, item);
foreach (WeakReference weakbindable in _associatedObjects)
{
var bindable = weakbindable.Target as BindableObject;
if (bindable == null)
continue;
item.AttachTo(bindable);
}
}
protected virtual void OnAttachedTo(BindableObject bindable)
{
lock(_associatedObjects)
{
_associatedObjects.Add(new WeakReference(bindable));
}
foreach (T item in this)
item.AttachTo(bindable);
}
protected virtual void OnDetachingFrom(BindableObject bindable)
{
foreach (T item in this)
item.DetachFrom(bindable);
lock(_associatedObjects)
{
for (var i = 0; i < _associatedObjects.Count; i++)
{
object target = _associatedObjects[i].Target;
if (target == null || target == bindable)
{
_associatedObjects.RemoveAt(i);
i--;
}
}
}
}
protected override void RemoveItem(int index)
{
T item = this[index];
foreach (WeakReference weakbindable in _associatedObjects)
{
var bindable = weakbindable.Target as BindableObject;
if (bindable == null)
continue;
item.DetachFrom(bindable);
}
base.RemoveItem(index);
}
protected override void SetItem(int index, T item)
{
T old = this[index];
foreach (WeakReference weakbindable in _associatedObjects)
{
var bindable = weakbindable.Target as BindableObject;
if (bindable == null)
continue;
old.DetachFrom(bindable);
}
base.SetItem(index, item);
foreach (WeakReference weakbindable in _associatedObjects)
{
var bindable = weakbindable.Target as BindableObject;
if (bindable == null)
continue;
item.AttachTo(bindable);
}
}
}
}
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