UIElementCollection.cs source code in C# .NET

Source code for the .NET framework in C#

                        

Code:

/ Dotnetfx_Vista_SP2 / Dotnetfx_Vista_SP2 / 8.0.50727.4016 / DEVDIV / depot / DevDiv / releases / Orcas / QFE / wpf / src / Framework / System / Windows / Controls / UIElementCollection.cs / 1 / UIElementCollection.cs

                            //---------------------------------------------------------------------------- 
//
// Copyright (C) Microsoft Corporation.  All rights reserved.
//
// File: UIElementCollection.cs 
//
// Description: Contains the UIElementCollection base class. 
// 
// History:
//  07/18/2003 : greglett  - Added to WCP branch 
//
//---------------------------------------------------------------------------

using MS.Internal; 
using System;
using System.Collections; 
using System.Windows.Media; 
using System.Windows.Threading;
using System.Windows.Markup; 

namespace System.Windows.Controls
{
    ///  
    /// A UIElementCollection is a ordered collection of UIElements.
    ///  
    ///  
    /// A UIElementCollection has implied context affinity. It is a violation to access
    /// the collection from a different context than that of the owning Panel. 
    /// 
    /// 
    public class UIElementCollection : IList
    { 
        /// 
        ///     The colleciton is the children collection of the visualParent. The logicalParent 
        ///     is used to do logical parenting. The flags is used to invalidate 
        ///     the resource properties in the child tree, if an Application object exists.
        ///  
        /// The element of whom this is a children collection
        /// The logicalParent of the elements of this collection.
        /// if overriding Panel.CreateUIElementCollection, pass the logicalParent parameter of that method here.
        ///  
        public UIElementCollection(UIElement visualParent, FrameworkElement logicalParent)
        { 
            if (visualParent == null) 
            {
                throw new ArgumentNullException(SR.Get(SRID.Panel_NoNullVisualParent, "visualParent", this.GetType())); 
            }

            _visualChildren = new VisualCollection(visualParent);
            _visualParent = visualParent; 
            _logicalParent = logicalParent;
        } 
 

        ///  
        /// Gets the number of elements in the collection.
        /// 
        public virtual int Count
        { 
            get { return _visualChildren.Count; }
        } 
 
        /// 
        /// Gets a value indicating whether access to the ICollection is synchronized (thread-safe). 
        /// For more details, see 
        /// 
        public virtual bool IsSynchronized
        { 
            get { return _visualChildren.IsSynchronized; }
        } 
 

        ///  
        /// For more details, see 
        /// 
        public virtual object SyncRoot
        { 
            get { return _visualChildren.SyncRoot; }
        } 
 
        /// 
        /// Copies the collection into the Array. 
        /// For more details, see 
        /// 
        public virtual void CopyTo(Array array, int index)
        { 
            _visualChildren.CopyTo(array, index);
        } 
 
        /// 
        /// Strongly typed version of CopyTo 
        /// Copies the collection into the Array.
        /// For more details, see 
        /// 
        public virtual void CopyTo(UIElement[] array, int index) 
        {
            _visualChildren.CopyTo(array, index); 
        } 

        ///  
        /// For more details, see 
        /// 
        public virtual int Capacity
        { 
            get { return _visualChildren.Capacity; }
            set 
            { 
                VerifyWriteAccess();
 
                _visualChildren.Capacity = value;
            }
        }
 
        /// 
        /// For more details, see  
        ///  
        public virtual UIElement this[int index]
        { 
            get { return _visualChildren[index] as UIElement; }
            set
            {
                VerifyWriteAccess(); 
                ValidateElement(value);
 
                VisualCollection vc = _visualChildren; 

                //if setting new element into slot or assigning null, 
                //remove previously hooked element from the logical tree
                if (vc[index] != value)
                {
                    UIElement e = vc[index] as UIElement; 
                    if (e != null)
                        ClearLogicalParent(e); 
 
                    vc[index] = value;
 
                    SetLogicalParent(value);

                    _visualParent.InvalidateMeasure();
                } 
            }
        } 
 
        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly. 
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator
        internal void SetInternal(int index, UIElement item)
        { 
            ValidateElement(item);
 
            VisualCollection vc = _visualChildren; 

            if(vc[index] != item) 
            {
                vc[index] = null; // explicitly disconnect the existing visual;
                vc[index] = item;
 
                _visualParent.InvalidateMeasure();
            } 
        } 

 
        /// 
        /// Adds the element to the UIElementCollection
        /// For more details, see 
        ///  
        public virtual int Add(UIElement element)
        { 
            VerifyWriteAccess(); 

            return AddInternal(element); 
        }

        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly. 
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator 
        internal int AddInternal(UIElement element) 
        {
            ValidateElement(element); 

            SetLogicalParent(element);
            int retVal = _visualChildren.Add(element);
 
            // invalidate measure on visual parent
            _visualParent.InvalidateMeasure(); 
 
            return retVal;
        } 

        /// 
        /// Returns the index of the element in the UIElementCollection
        /// For more details, see  
        /// 
        public virtual int IndexOf(UIElement element) 
        { 
            return _visualChildren.IndexOf(element);
        } 

        /// 
        /// Removes the specified element from the UIElementCollection.
        /// For more details, see  
        /// 
        public virtual void Remove(UIElement element) 
        { 
            VerifyWriteAccess();
 
            _visualChildren.Remove(element);
            ClearLogicalParent(element);
            _visualParent.InvalidateMeasure();
        } 

        ///  
        /// Removes the specified element from the UIElementCollection. 
        /// Used only by ItemsControl and by VirtualizingStackPanel
        /// For more details, see  
        /// 
        internal virtual void RemoveNoVerify(UIElement element)
        {
            _visualChildren.Remove(element); 
        }
 
        ///  
        /// Determines whether a element is in the UIElementCollection.
        /// For more details, see  
        /// 
        public virtual bool Contains(UIElement element)
        {
            return _visualChildren.Contains(element); 
        }
 
        ///  
        /// Removes all elements from the UIElementCollection.
        /// For more details, see  
        /// 
        public virtual void Clear()
        {
            VerifyWriteAccess(); 

            ClearInternal(); 
        } 

 
        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly.
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator 
        internal void ClearInternal()
        { 
            VisualCollection vc = _visualChildren; 
            int cnt = vc.Count;
 
            if (cnt > 0)
            {
                // copy children in VisualCollection so that we can clear the visual link first,
                // followed by the logical link 
                Visual[] visuals = new Visual[cnt];
                for (int i = 0; i < cnt; i++) 
                { 
                    visuals[i] = vc[i];
                } 

                vc.Clear();

                //disconnect from logical tree 
                for (int i = 0; i < cnt; i++)
                { 
                    UIElement e = visuals[i] as UIElement; 
                    if (e != null)
                    { 
                        ClearLogicalParent(e);
                    }
                }
 
                _visualParent.InvalidateMeasure();
            } 
        } 

        ///  
        /// Inserts an element into the UIElementCollection at the specified index.
        /// For more details, see 
        /// 
        public virtual void Insert(int index, UIElement element) 
        {
            VerifyWriteAccess(); 
 
            InsertInternal(index, element);
        } 

        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly.
        // Don't call this unless you are deriving a panel that is populating the collection 
        // in cooperation with the generator
        internal void InsertInternal(int index, UIElement element) 
        { 
            ValidateElement(element);
 
            SetLogicalParent(element);
            _visualChildren.Insert(index, element);
            _visualParent.InvalidateMeasure();
        } 

        ///  
        /// Removes the UIElement at the specified index. 
        /// For more details, see 
        ///  
        public virtual void RemoveAt(int index)
        {
            VerifyWriteAccess();
 
            VisualCollection vc = _visualChildren;
 
            //disconnect from logical tree 
            UIElement e = vc[index] as UIElement;
 
            vc.RemoveAt(index);

            if (e != null)
                ClearLogicalParent(e); 

            _visualParent.InvalidateMeasure(); 
        } 

 
        /// 
        /// Removes a range of Visuals from the VisualCollection.
        /// For more details, see 
        ///  
        public virtual void RemoveRange(int index, int count)
        { 
            VerifyWriteAccess(); 

            RemoveRangeInternal(index, count); 
        }

        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly. 
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator 
        internal void RemoveRangeInternal(int index, int count) 
        {
            VisualCollection vc = _visualChildren; 
            int cnt = vc.Count;
            if (count > (cnt - index))
            {
                count = cnt - index; 
            }
 
            if (count > 0) 
            {
                // copy children in VisualCollection so that we can clear the visual link first, 
                // followed by the logical link
                Visual[] visuals = new Visual[count];
                int i = index;
                for (int loop = 0; loop < count; i++, loop++) 
                {
                    visuals[loop] = vc[i]; 
                } 

                vc.RemoveRange(index, count); 

                //disconnect from logical tree
                for (i = 0; i < count; i++)
                { 
                    UIElement e = visuals[i] as UIElement;
                    if (e != null) 
                    { 
                        ClearLogicalParent(e);
                    } 
                }

                _visualParent.InvalidateMeasure();
            } 

        } 
 

        ///  
        /// Method that forwards to VisualCollection.Move
        /// 
        /// 
        ///  
        internal void MoveVisualChild(Visual visual, Visual destination)
        { 
            _visualChildren.Move(visual, destination); 
        }
 		 
        private UIElement Cast(object value)
        {
            if (value == null)
                throw new System.ArgumentException(SR.Get(SRID.Collection_NoNull, "UIElementCollection")); 

            UIElement element = value as UIElement; 
 
            if (element == null)
                throw new System.ArgumentException(SR.Get(SRID.Collection_BadType, "UIElementCollection", value.GetType().Name, "UIElement")); 

            return element;
        }
		 
        #region IList Members
 
        ///  
        /// Adds an element to the UIElementCollection
        ///  
        int IList.Add(object value)
        {
            return Add(Cast(value));
        } 

        ///  
        /// Determines whether an element is in the UIElementCollection. 
        /// 
        bool IList.Contains(object value) 
        {
            return Contains(value as UIElement);
        }
 
        /// 
        /// Returns the index of the element in the UIElementCollection 
        ///  
        int IList.IndexOf(object value)
        { 
            return IndexOf(value as UIElement);
        }

        ///  
        /// Inserts an element into the UIElementCollection
        ///  
        void IList.Insert(int index, object value) 
        {
            Insert(index, Cast(value)); 
        }

        /// 
        ///  
        bool IList.IsFixedSize
        { 
            get { return false; } 
        }
 
        /// 
        /// 
        bool IList.IsReadOnly
        { 
            get { return false; }
        } 
 
        /// 
        /// Removes an element from the UIElementCollection 
        /// 
        void IList.Remove(object value)
        {
            Remove(value as UIElement); 
        }
 
        ///  
        /// For more details, see 
        ///  
        object IList.this[int index]
        {
            get
            { 
                return this[index];
            } 
            set 
            {
                this[index] = Cast(value); 
            }
        }

        #endregion 

 
        // --------------------------------------------------------------- 
        // IEnumerable Interface
        // --------------------------------------------------------------- 


        /// 
        /// Returns an enumerator that can iterate through the collection. 
        /// 
        /// Enumerator that enumerates the collection in order. 
        public virtual IEnumerator GetEnumerator() 
        {
            return _visualChildren.GetEnumerator(); 
        }

        /// 
        ///     This method does logical parenting of the given element. 
        /// 
        ///  
        protected void SetLogicalParent(UIElement element) 
        {
            if (_logicalParent != null) 
            {
                _logicalParent.AddLogicalChild(element);
            }
        } 

        ///  
        ///     This method removes logical parenting when element goes away from the collection. 
        /// 
        ///  
        protected void ClearLogicalParent(UIElement element)
        {
            if (_logicalParent != null)
            { 
                _logicalParent.RemoveLogicalChild(element);
            } 
        } 

        ///  
        /// Provides access to visual parent.
        /// 
        internal UIElement VisualParent
        { 
            get { return (_visualParent); }
        } 
 
        // Helper function to validate element; will throw exceptions if problems are detected.
        private void ValidateElement(UIElement element) 
        {
            if (element == null)
            {
                throw new ArgumentNullException(SR.Get(SRID.Panel_NoNullChildren, this.GetType())); 
            }
        } 
 
        private void VerifyWriteAccess()
        { 
            Panel p = _visualParent as Panel;
            if (p != null && p.IsDataBound)
            {
                throw new InvalidOperationException(SR.Get(SRID.Panel_BoundPanel_NoChildren)); 
            }
        } 
 
        private readonly VisualCollection _visualChildren;
        private readonly UIElement _visualParent; 
        private readonly FrameworkElement _logicalParent;

    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
//---------------------------------------------------------------------------- 
//
// Copyright (C) Microsoft Corporation.  All rights reserved.
//
// File: UIElementCollection.cs 
//
// Description: Contains the UIElementCollection base class. 
// 
// History:
//  07/18/2003 : greglett  - Added to WCP branch 
//
//---------------------------------------------------------------------------

using MS.Internal; 
using System;
using System.Collections; 
using System.Windows.Media; 
using System.Windows.Threading;
using System.Windows.Markup; 

namespace System.Windows.Controls
{
    ///  
    /// A UIElementCollection is a ordered collection of UIElements.
    ///  
    ///  
    /// A UIElementCollection has implied context affinity. It is a violation to access
    /// the collection from a different context than that of the owning Panel. 
    /// 
    /// 
    public class UIElementCollection : IList
    { 
        /// 
        ///     The colleciton is the children collection of the visualParent. The logicalParent 
        ///     is used to do logical parenting. The flags is used to invalidate 
        ///     the resource properties in the child tree, if an Application object exists.
        ///  
        /// The element of whom this is a children collection
        /// The logicalParent of the elements of this collection.
        /// if overriding Panel.CreateUIElementCollection, pass the logicalParent parameter of that method here.
        ///  
        public UIElementCollection(UIElement visualParent, FrameworkElement logicalParent)
        { 
            if (visualParent == null) 
            {
                throw new ArgumentNullException(SR.Get(SRID.Panel_NoNullVisualParent, "visualParent", this.GetType())); 
            }

            _visualChildren = new VisualCollection(visualParent);
            _visualParent = visualParent; 
            _logicalParent = logicalParent;
        } 
 

        ///  
        /// Gets the number of elements in the collection.
        /// 
        public virtual int Count
        { 
            get { return _visualChildren.Count; }
        } 
 
        /// 
        /// Gets a value indicating whether access to the ICollection is synchronized (thread-safe). 
        /// For more details, see 
        /// 
        public virtual bool IsSynchronized
        { 
            get { return _visualChildren.IsSynchronized; }
        } 
 

        ///  
        /// For more details, see 
        /// 
        public virtual object SyncRoot
        { 
            get { return _visualChildren.SyncRoot; }
        } 
 
        /// 
        /// Copies the collection into the Array. 
        /// For more details, see 
        /// 
        public virtual void CopyTo(Array array, int index)
        { 
            _visualChildren.CopyTo(array, index);
        } 
 
        /// 
        /// Strongly typed version of CopyTo 
        /// Copies the collection into the Array.
        /// For more details, see 
        /// 
        public virtual void CopyTo(UIElement[] array, int index) 
        {
            _visualChildren.CopyTo(array, index); 
        } 

        ///  
        /// For more details, see 
        /// 
        public virtual int Capacity
        { 
            get { return _visualChildren.Capacity; }
            set 
            { 
                VerifyWriteAccess();
 
                _visualChildren.Capacity = value;
            }
        }
 
        /// 
        /// For more details, see  
        ///  
        public virtual UIElement this[int index]
        { 
            get { return _visualChildren[index] as UIElement; }
            set
            {
                VerifyWriteAccess(); 
                ValidateElement(value);
 
                VisualCollection vc = _visualChildren; 

                //if setting new element into slot or assigning null, 
                //remove previously hooked element from the logical tree
                if (vc[index] != value)
                {
                    UIElement e = vc[index] as UIElement; 
                    if (e != null)
                        ClearLogicalParent(e); 
 
                    vc[index] = value;
 
                    SetLogicalParent(value);

                    _visualParent.InvalidateMeasure();
                } 
            }
        } 
 
        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly. 
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator
        internal void SetInternal(int index, UIElement item)
        { 
            ValidateElement(item);
 
            VisualCollection vc = _visualChildren; 

            if(vc[index] != item) 
            {
                vc[index] = null; // explicitly disconnect the existing visual;
                vc[index] = item;
 
                _visualParent.InvalidateMeasure();
            } 
        } 

 
        /// 
        /// Adds the element to the UIElementCollection
        /// For more details, see 
        ///  
        public virtual int Add(UIElement element)
        { 
            VerifyWriteAccess(); 

            return AddInternal(element); 
        }

        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly. 
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator 
        internal int AddInternal(UIElement element) 
        {
            ValidateElement(element); 

            SetLogicalParent(element);
            int retVal = _visualChildren.Add(element);
 
            // invalidate measure on visual parent
            _visualParent.InvalidateMeasure(); 
 
            return retVal;
        } 

        /// 
        /// Returns the index of the element in the UIElementCollection
        /// For more details, see  
        /// 
        public virtual int IndexOf(UIElement element) 
        { 
            return _visualChildren.IndexOf(element);
        } 

        /// 
        /// Removes the specified element from the UIElementCollection.
        /// For more details, see  
        /// 
        public virtual void Remove(UIElement element) 
        { 
            VerifyWriteAccess();
 
            _visualChildren.Remove(element);
            ClearLogicalParent(element);
            _visualParent.InvalidateMeasure();
        } 

        ///  
        /// Removes the specified element from the UIElementCollection. 
        /// Used only by ItemsControl and by VirtualizingStackPanel
        /// For more details, see  
        /// 
        internal virtual void RemoveNoVerify(UIElement element)
        {
            _visualChildren.Remove(element); 
        }
 
        ///  
        /// Determines whether a element is in the UIElementCollection.
        /// For more details, see  
        /// 
        public virtual bool Contains(UIElement element)
        {
            return _visualChildren.Contains(element); 
        }
 
        ///  
        /// Removes all elements from the UIElementCollection.
        /// For more details, see  
        /// 
        public virtual void Clear()
        {
            VerifyWriteAccess(); 

            ClearInternal(); 
        } 

 
        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly.
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator 
        internal void ClearInternal()
        { 
            VisualCollection vc = _visualChildren; 
            int cnt = vc.Count;
 
            if (cnt > 0)
            {
                // copy children in VisualCollection so that we can clear the visual link first,
                // followed by the logical link 
                Visual[] visuals = new Visual[cnt];
                for (int i = 0; i < cnt; i++) 
                { 
                    visuals[i] = vc[i];
                } 

                vc.Clear();

                //disconnect from logical tree 
                for (int i = 0; i < cnt; i++)
                { 
                    UIElement e = visuals[i] as UIElement; 
                    if (e != null)
                    { 
                        ClearLogicalParent(e);
                    }
                }
 
                _visualParent.InvalidateMeasure();
            } 
        } 

        ///  
        /// Inserts an element into the UIElementCollection at the specified index.
        /// For more details, see 
        /// 
        public virtual void Insert(int index, UIElement element) 
        {
            VerifyWriteAccess(); 
 
            InsertInternal(index, element);
        } 

        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly.
        // Don't call this unless you are deriving a panel that is populating the collection 
        // in cooperation with the generator
        internal void InsertInternal(int index, UIElement element) 
        { 
            ValidateElement(element);
 
            SetLogicalParent(element);
            _visualChildren.Insert(index, element);
            _visualParent.InvalidateMeasure();
        } 

        ///  
        /// Removes the UIElement at the specified index. 
        /// For more details, see 
        ///  
        public virtual void RemoveAt(int index)
        {
            VerifyWriteAccess();
 
            VisualCollection vc = _visualChildren;
 
            //disconnect from logical tree 
            UIElement e = vc[index] as UIElement;
 
            vc.RemoveAt(index);

            if (e != null)
                ClearLogicalParent(e); 

            _visualParent.InvalidateMeasure(); 
        } 

 
        /// 
        /// Removes a range of Visuals from the VisualCollection.
        /// For more details, see 
        ///  
        public virtual void RemoveRange(int index, int count)
        { 
            VerifyWriteAccess(); 

            RemoveRangeInternal(index, count); 
        }

        // Warning: this method is very dangerous because it does not prevent adding children
        // into collection populated by generator. This may cause crashes if used incorrectly. 
        // Don't call this unless you are deriving a panel that is populating the collection
        // in cooperation with the generator 
        internal void RemoveRangeInternal(int index, int count) 
        {
            VisualCollection vc = _visualChildren; 
            int cnt = vc.Count;
            if (count > (cnt - index))
            {
                count = cnt - index; 
            }
 
            if (count > 0) 
            {
                // copy children in VisualCollection so that we can clear the visual link first, 
                // followed by the logical link
                Visual[] visuals = new Visual[count];
                int i = index;
                for (int loop = 0; loop < count; i++, loop++) 
                {
                    visuals[loop] = vc[i]; 
                } 

                vc.RemoveRange(index, count); 

                //disconnect from logical tree
                for (i = 0; i < count; i++)
                { 
                    UIElement e = visuals[i] as UIElement;
                    if (e != null) 
                    { 
                        ClearLogicalParent(e);
                    } 
                }

                _visualParent.InvalidateMeasure();
            } 

        } 
 

        ///  
        /// Method that forwards to VisualCollection.Move
        /// 
        /// 
        ///  
        internal void MoveVisualChild(Visual visual, Visual destination)
        { 
            _visualChildren.Move(visual, destination); 
        }
 		 
        private UIElement Cast(object value)
        {
            if (value == null)
                throw new System.ArgumentException(SR.Get(SRID.Collection_NoNull, "UIElementCollection")); 

            UIElement element = value as UIElement; 
 
            if (element == null)
                throw new System.ArgumentException(SR.Get(SRID.Collection_BadType, "UIElementCollection", value.GetType().Name, "UIElement")); 

            return element;
        }
		 
        #region IList Members
 
        ///  
        /// Adds an element to the UIElementCollection
        ///  
        int IList.Add(object value)
        {
            return Add(Cast(value));
        } 

        ///  
        /// Determines whether an element is in the UIElementCollection. 
        /// 
        bool IList.Contains(object value) 
        {
            return Contains(value as UIElement);
        }
 
        /// 
        /// Returns the index of the element in the UIElementCollection 
        ///  
        int IList.IndexOf(object value)
        { 
            return IndexOf(value as UIElement);
        }

        ///  
        /// Inserts an element into the UIElementCollection
        ///  
        void IList.Insert(int index, object value) 
        {
            Insert(index, Cast(value)); 
        }

        /// 
        ///  
        bool IList.IsFixedSize
        { 
            get { return false; } 
        }
 
        /// 
        /// 
        bool IList.IsReadOnly
        { 
            get { return false; }
        } 
 
        /// 
        /// Removes an element from the UIElementCollection 
        /// 
        void IList.Remove(object value)
        {
            Remove(value as UIElement); 
        }
 
        ///  
        /// For more details, see 
        ///  
        object IList.this[int index]
        {
            get
            { 
                return this[index];
            } 
            set 
            {
                this[index] = Cast(value); 
            }
        }

        #endregion 

 
        // --------------------------------------------------------------- 
        // IEnumerable Interface
        // --------------------------------------------------------------- 


        /// 
        /// Returns an enumerator that can iterate through the collection. 
        /// 
        /// Enumerator that enumerates the collection in order. 
        public virtual IEnumerator GetEnumerator() 
        {
            return _visualChildren.GetEnumerator(); 
        }

        /// 
        ///     This method does logical parenting of the given element. 
        /// 
        ///  
        protected void SetLogicalParent(UIElement element) 
        {
            if (_logicalParent != null) 
            {
                _logicalParent.AddLogicalChild(element);
            }
        } 

        ///  
        ///     This method removes logical parenting when element goes away from the collection. 
        /// 
        ///  
        protected void ClearLogicalParent(UIElement element)
        {
            if (_logicalParent != null)
            { 
                _logicalParent.RemoveLogicalChild(element);
            } 
        } 

        ///  
        /// Provides access to visual parent.
        /// 
        internal UIElement VisualParent
        { 
            get { return (_visualParent); }
        } 
 
        // Helper function to validate element; will throw exceptions if problems are detected.
        private void ValidateElement(UIElement element) 
        {
            if (element == null)
            {
                throw new ArgumentNullException(SR.Get(SRID.Panel_NoNullChildren, this.GetType())); 
            }
        } 
 
        private void VerifyWriteAccess()
        { 
            Panel p = _visualParent as Panel;
            if (p != null && p.IsDataBound)
            {
                throw new InvalidOperationException(SR.Get(SRID.Panel_BoundPanel_NoChildren)); 
            }
        } 
 
        private readonly VisualCollection _visualChildren;
        private readonly UIElement _visualParent; 
        private readonly FrameworkElement _logicalParent;

    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
                        

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