/// <summary>
/// 向集合添加指定项
/// </summary>
/// <param name="item">待添加项</param>
public new void Add(DropDownButtonItem item)
{
base.Add(item);
AfterItemAdded?.Invoke(this, new DropDownButtonItemCollectionChangedEventArgs(item));
}
public void Enqueue(T item)
{
_items.Add(item);
AfterItemAdded?.Invoke(this, new QueueItemAddedEventArgs <T>(item));
}