//----------------------------------------------------------------
// Copyright (c) Microsoft Corporation.  All rights reserved.
//----------------------------------------------------------------
 
namespace System.Activities.Presentation 
{
    using System.Diagnostics.CodeAnalysis;
 
 
    using System;
    using System.Collections.Generic;
 
    // <summary>
    // The ContextItem class is the base class from which all context items must derive.
    // </summary>
    public abstract class ContextItem 
    {
 
        // <summary>
        // Creates a new ContextItem.
        // </summary>
        protected ContextItem() 
        {
        }
 
        // <summary>
        // Returns the item type for this editing context item.  Context items are
        // considered unique based on their item type.  By using ItemType to identify
        // a type of context item we allow several derived versions of context items to
        // be cataloged under the same key in the editing context.
        // </summary>
        // <value></value>
        public abstract Type ItemType 
        { get; }
 
        // <summary>
        // This method is called on a context item before it is stored in the context item
        // manager.  The previous item in the context item manager is passed.
        // </summary>
        // <param name="context">The editing context that is making this change.</param>
        // <param name="previousItem">The previously active item in the context.  Because items must have default constructors a default item will be fabricated if an item is first passed into the context.</param>
        // <returns></returns>
        protected virtual void OnItemChanged(EditingContext context, ContextItem previousItem) 
        {
        }
 
        //
        // Internal API that calls OnItemChanged.  This is invoked from the
        // abstract ContextItemManager class so deriving classes can still
        // invoke it.
        //
        internal void InvokeOnItemChanged(EditingContext context, ContextItem previousItem) 
        {
            OnItemChanged(context, previousItem);
        }
    }
}