/***************************************************************************\
*
* File: InheritanceContextHelper.cs
*
* This file holds a helper class for DO subclasses that implement an
* inheritance context.
*
* Copyright (C) by Microsoft Corporation.  All rights reserved.
*
\***************************************************************************/
 
 
using System;
using System.Windows;
using MS.Internal.WindowsBase;
 
namespace MS.Internal
{
    internal static class InheritanceContextHelper
    {
 
 
        //--------------------------------------------------------------------
        //
        //  ProvideContextForObject
        //
        //  Tell a DO that it has a new inheritance context available.
        //
        //--------------------------------------------------------------------
 
        [FriendAccessAllowed] // Built into Core, also used by Framework.
        internal static void ProvideContextForObject(
            DependencyObject context,
            DependencyObject newValue )
        {
            if (context != null)
            {
                context.ProvideSelfAsInheritanceContext(newValue, null);
            }
        }
 
        //--------------------------------------------------------------------
        //
        //  RemoveContextFromObject
        //
        //  Tell a DO that it has lost its inheritance context.
        //
        //--------------------------------------------------------------------
 
        [FriendAccessAllowed] // Built into Base, also used by Framework.
        internal static void RemoveContextFromObject(
            DependencyObject context,
            DependencyObject oldValue )
        {
            if (context != null && oldValue.InheritanceContext == context)
            {
                context.RemoveSelfAsInheritanceContext(oldValue, null);
            }
        }
 
 
 
        //--------------------------------------------------------------------
        //
        //  AddInheritanceContext
        //
        //  Implementation to receive a new inheritance context
        //
        //--------------------------------------------------------------------
 
        [FriendAccessAllowed] // Built into Base, also used by Framework.
        internal static void AddInheritanceContext(DependencyObject newInheritanceContext,
                                                              DependencyObject value,
                                                              ref bool hasMultipleInheritanceContexts,
                                                              ref DependencyObject inheritanceContext )
        {
            // ignore the request when the new context is the same as the old,
            // or when there are already multiple contexts
            if (newInheritanceContext != inheritanceContext &&
                !hasMultipleInheritanceContexts)
            {
                if (inheritanceContext == null || newInheritanceContext == null)
                {
                    // Pick up the new context
                    inheritanceContext = newInheritanceContext;
                }
                else
                {
                    // We are now being referenced from multiple
                    // places, clear the context
                    hasMultipleInheritanceContexts = true;
                    inheritanceContext = null;
                }
 
                value.OnInheritanceContextChanged(EventArgs.Empty);
            }
        }
 
 
        //--------------------------------------------------------------------
        //
        //  RemoveInheritanceContext
        //
        //  Implementation to remove an old inheritance context
        //
        //--------------------------------------------------------------------
 
        [FriendAccessAllowed] // Built into Base, also used by Framework.
        internal static void RemoveInheritanceContext(DependencyObject oldInheritanceContext,
                                                              DependencyObject value,
                                                              ref bool hasMultipleInheritanceContexts,
                                                              ref DependencyObject inheritanceContext )
        {
            // ignore the request when the given context doesn't match the old one,
            // or when there are already multiple contexts
            if (oldInheritanceContext == inheritanceContext &&
                !hasMultipleInheritanceContexts)
            {
                // clear the context
                inheritanceContext = null;
                value.OnInheritanceContextChanged(EventArgs.Empty);
            }
        }
    }
}