Nuclex.Support/Source/Collections/ParentingCollection.cs

#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2017 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion

using System;
using System.Collections.ObjectModel;

namespace Nuclex.Support.Collections {

  /// <summary>Collection that automatically assigns an owner to all its elements</summary>
  /// <remarks>
  ///   This collection automatically assigns a parent object to elements that
  ///   are managed in it. The elements have to derive from the Parentable&lt;&gt;
  ///   base class.
  /// </remarks>
  /// <typeparam name="TParent">Type of the parent object to assign to items</typeparam>
  /// <typeparam name="TItem">Type of the items being managed in the collection</typeparam>
  public class ParentingCollection<TParent, TItem> : Collection<TItem>
    where TItem : Parentable<TParent> {

    /// <summary>Reparents all elements in the collection</summary>
    /// <param name="parent">New parent to take ownership of the items</param>
    protected void Reparent(TParent parent) {
      this.parent = parent;

      for(int index = 0; index < Count; ++index)
        base[index].SetParent(parent);
    }

    /// <summary>Clears all elements from the collection</summary>
    protected override void ClearItems() {
      for(int index = 0; index < Count; ++index)
        base[index].SetParent(default(TParent));

      base.ClearItems();
    }

    /// <summary>Inserts a new element into the collection</summary>
    /// <param name="index">Index at which to insert the element</param>
    /// <param name="item">Item to be inserted</param>
    protected override void InsertItem(int index, TItem item) {
      base.InsertItem(index, item);
      item.SetParent(this.parent);
    }

    /// <summary>Removes an element from the collection</summary>
    /// <param name="index">Index of the element to remove</param>
    protected override void RemoveItem(int index) {
      base[index].SetParent(default(TParent));
      base.RemoveItem(index);
    }

    /// <summary>Takes over a new element that is directly assigned</summary>
    /// <param name="index">Index of the element that was assigned</param>
    /// <param name="item">New item</param>
    protected override void SetItem(int index, TItem item) {
      base[index].SetParent(default(TParent));
      base.SetItem(index, item);
      item.SetParent(this.parent);
    }

    /// <summary>Disposes all items contained in the collection</summary>
    /// <remarks>
    ///   <para>
    ///     This method is intended to support collections that need to dispose their
    ///     items. It will unparent all of the collection's items and call Dispose()
    ///     on any item that implements IDisposable.
    ///   </para>
    ///   <para>
    ///     Do not call this method from your destructor as it will access the
    ///     contained items in order to unparent and to Dispose() them, which leads
    ///     to undefined behavior since the object might have already been collected
    ///     by the GC. Call it only if your object is being manually disposed.
    ///   </para>
    /// </remarks>
    protected void DisposeItems() {

      // Dispose all the items in the collection that implement IDisposable,
      // starting from the last item in the assumption that this is the fastest
      // way to empty a list without causing excessive shiftings in the array.
      for(int index = base.Count - 1; index >= 0; --index) {
        IDisposable disposable = base[index] as IDisposable;

        // If the item is disposable, destroy it now
        if(disposable != null) {
          disposable.Dispose();
        }
      }

      base.ClearItems();

    }

    /// <summary>Parent this collection currently belongs to</summary>
    private TParent parent;

  }

} // namespace Nuclex.Support.Collections