//---------------------------------------------------------------------------
//
// File: DeferredReference.cs
//
// Copyright (C) Microsoft Corporation.  All rights reserved.
//
// Description: Proxy object passed to the property system to delay load values.
//
//---------------------------------------------------------------------------
 
namespace System.Windows
{
    using MS.Internal.WindowsBase;  // FriendAccessAllowed
 
    // Proxy object passed to the property system to delay load values.
    //
    // The property system will make a GetValue callback (dereferencing the
    // reference) inside DependencyProperty.GetValue calls, or before
    // coercion callbacks to derived classes.
    //
    // DeferredReference instances are passed directly to ValidateValue
    // callbacks (which always go to the DependencyProperty owner class),
    // and also to CoerceValue callbacks on the owner class only.  THEREFORE,
    // IT IS 
 
    [FriendAccessAllowed] // Built into Base, also used by Core & Framework.
    internal abstract class DeferredReference
    {
        //------------------------------------------------------
        //
        //  Internal Methods
        //
        //------------------------------------------------------
 
        #region Internal Methods
 
        // Deferences a property value on demand.
        internal abstract object GetValue(BaseValueSourceInternal valueSource);
 
        // Gets the type of the value it represents
        internal abstract Type GetValueType();
 
        #endregion Internal Methods
    }
 
    internal class DeferredMutableDefaultReference : DeferredReference
    {
        #region Constructor
 
        internal DeferredMutableDefaultReference(PropertyMetadata metadata, DependencyObject d, DependencyProperty dp)
        {
            _sourceObject = d;
            _sourceProperty = dp;
            _sourceMetadata = metadata;
        }
 
        #endregion Constructor
 
        #region Methods
 
        internal override object GetValue(BaseValueSourceInternal valueSource)
        {
            return _sourceMetadata.GetDefaultValue(_sourceObject, _sourceProperty);
        }
 
        // Gets the type of the value it represents
        internal override Type GetValueType()
        {
            return _sourceProperty.PropertyType;
        }
 
        #endregion Methods
 
        #region Properties
 
        internal PropertyMetadata SourceMetadata
        {
            get { return _sourceMetadata; }
        }
 
        protected DependencyObject SourceObject
        {
            get { return _sourceObject; }
        }
 
        protected DependencyProperty SourceProperty
        {
            get { return _sourceProperty; }
        }
 
        #endregion Properties
 
        #region Data
 
        private readonly PropertyMetadata _sourceMetadata;
        private readonly DependencyObject _sourceObject;
        private readonly DependencyProperty _sourceProperty;
 
        #endregion Data
    }
 
 
}