UncommonField.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / System / Windows / UncommonField.cs / 1305600 / UncommonField.cs
                        
                        
                            using System; 
using System.Diagnostics;
using System.Security.Permissions;

using MS.Internal.WindowsBase;  // for FriendAccessAllowed 

namespace System.Windows 
{ 
    /// 
    /// 
    /// 
    //CASRemoval:[StrongNameIdentityPermissionAttribute(SecurityAction.InheritanceDemand, PublicKey=Microsoft.Internal.BuildInfo.WCP_PUBLIC_KEY_STRING)]
    [FriendAccessAllowed] // Built into Base, used by Core and Framework
    internal class UncommonField 
    {
        ///  
        ///     Create a new UncommonField. 
        /// 
        public UncommonField() : this(default(T)) 
        {
        }

        ///  
        ///     Create a new UncommonField.
        ///  
        /// The default value of the field. 
        public UncommonField(T defaultValue)
        { 
            _defaultValue = defaultValue;
            _hasBeenSet = false;

            lock (DependencyProperty.Synchronized) 
            {
                _globalIndex = DependencyProperty.GetUniqueGlobalIndex(null, null); 
 
                DependencyProperty.RegisteredPropertyList.Add();
            } 
        }

        /// 
        ///     Write the given value onto a DependencyObject instance. 
        /// 
        /// The DependencyObject on which to set the value. 
        /// The value to set. 
        public void SetValue(DependencyObject instance, T value)
        { 
            if (instance != null)
            {
                EntryIndex entryIndex = instance.LookupEntry(_globalIndex);
 
                // Set the value if it's not the default, otherwise remove the value.
                if (!object.ReferenceEquals(value, _defaultValue)) 
                { 
                    instance.SetEffectiveValue(entryIndex, null /* dp */, _globalIndex, null /* metadata */, value, BaseValueSourceInternal.Local);
                    _hasBeenSet = true; 
                }
                else
                {
                    instance.UnsetEffectiveValue(entryIndex, null /* dp */, null /* metadata */); 
                }
            } 
            else 
            {
                throw new ArgumentNullException("instance"); 
            }
        }

        ///  
        ///     Read the value of this field on a DependencyObject instance.
        ///  
        /// The DependencyObject from which to get the value. 
        /// 
        public T GetValue(DependencyObject instance) 
        {
            if (instance != null)
            {
                if (_hasBeenSet) 
                {
                    EntryIndex entryIndex = instance.LookupEntry(_globalIndex); 
 
                    if (entryIndex.Found)
                    { 
                        object value = instance.EffectiveValues[entryIndex.Index].LocalValue;

                        if (value != DependencyProperty.UnsetValue)
                        { 
                            return (T)value;
                        } 
                    } 
                    return _defaultValue;
                } 
                else
                {
                    return _defaultValue;
                } 
            }
            else 
            { 
                throw new ArgumentNullException("instance");
            } 
        }


        ///  
        ///     Clear this field from the given DependencyObject instance.
        ///  
        ///  
        public void ClearValue(DependencyObject instance)
        { 
            if (instance != null)
            {
                EntryIndex entryIndex = instance.LookupEntry(_globalIndex);
 
                instance.UnsetEffectiveValue(entryIndex, null /* dp */, null /* metadata */);
            } 
            else 
            {
                throw new ArgumentNullException("instance"); 
            }
        }

        internal int GlobalIndex 
        {
            get 
            { 
                return _globalIndex;
            } 
        }

        #region Private Fields
 
        private T _defaultValue;
        private int _globalIndex; 
        private bool _hasBeenSet; 

        #endregion 
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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UncommonField.cs source code in C# .NET

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