nulltextcontainer.cs source code in C# .NET

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Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Framework / System / Windows / Documents / nulltextcontainer.cs / 1305600 / nulltextcontainer.cs
                        

                        
                            //---------------------------------------------------------------------------- 
// 
//      Copyright (C) 2003 by Microsoft Corporation.  All rights reserved.
// 
// 
// Description:
//      NullTextContainer is an immutable empty TextContainer that contains 
//      single collapsed Start/End position. This is primarily used internally 
//      so parameter check is mostly replaced with debug assert.
// 
// History:
//      07/14/2004 - Zhenbin Xu (ZhenbinX) - Created.
//
//--------------------------------------------------------------------------- 
namespace System.Windows.Documents
{ 
    using System; 
    using System.Diagnostics;
    using System.Windows.Threading; 
    using System.Windows;                // DependencyID etc.
    using MS.Internal.Documents;
    using MS.Internal;
 
    //=====================================================================
    ///  
    /// NullTextContainer is an immutable empty TextContainer that contains 
    /// single collapsed Start/End position. This is primarily used internally
    /// so parameter check is mostly replaced with debug assert. 
    /// 
    internal sealed class NullTextContainer : ITextContainer
    {
        //------------------------------------------------------------------- 
        //
        // Connstructors 
        // 
        //----------------------------------------------------------------------
 
        #region Constructors

        internal NullTextContainer()
        { 
            _start  = new NullTextPointer(this, LogicalDirection.Backward);
            _end    = new NullTextPointer(this, LogicalDirection.Forward); 
        } 
        #endregion Constructors
 
        //-------------------------------------------------------------------
        //
        // Public Methods
        // 
        //----------------------------------------------------------------------
        #region Public Methods 
 
        //
        // This is readonly Text OM. All modification methods returns false 
        //

        void ITextContainer.BeginChange()
        { 
        }
 
        ///  
        /// 
        ///  
        void ITextContainer.BeginChangeNoUndo()
        {
            // We don't support undo, so follow the BeginChange codepath.
            ((ITextContainer)this).BeginChange(); 
        }
 
        ///  
        /// 
        void ITextContainer.EndChange() 
        {
            ((ITextContainer)this).EndChange(false /* skipEvents */);
        }
 
        /// 
        ///  
        void ITextContainer.EndChange(bool skipEvents) 
        {
        } 

        // Allocate a new ITextPointer at the specified offset.
        // Equivalent to this.Start.CreatePointer(offset), but does not
        // necessarily allocate this.Start. 
        ITextPointer ITextContainer.CreatePointerAtOffset(int offset, LogicalDirection direction)
        { 
            return ((ITextContainer)this).Start.CreatePointer(offset, direction); 
        }
 
        // Not Implemented.
        ITextPointer ITextContainer.CreatePointerAtCharOffset(int charOffset, LogicalDirection direction)
        {
            throw new NotImplementedException(); 
        }
 
        ITextPointer ITextContainer.CreateDynamicTextPointer(StaticTextPointer position, LogicalDirection direction) 
        {
            return ((ITextPointer)position.Handle0).CreatePointer(direction); 
        }

        StaticTextPointer ITextContainer.CreateStaticPointerAtOffset(int offset)
        { 
            return new StaticTextPointer(this, ((ITextContainer)this).CreatePointerAtOffset(offset, LogicalDirection.Forward));
        } 
 
        TextPointerContext ITextContainer.GetPointerContext(StaticTextPointer pointer, LogicalDirection direction)
        { 
            return ((ITextPointer)pointer.Handle0).GetPointerContext(direction);
        }

        int ITextContainer.GetOffsetToPosition(StaticTextPointer position1, StaticTextPointer position2) 
        {
            return ((ITextPointer)position1.Handle0).GetOffsetToPosition((ITextPointer)position2.Handle0); 
        } 

        int ITextContainer.GetTextInRun(StaticTextPointer position, LogicalDirection direction, char[] textBuffer, int startIndex, int count) 
        {
            return ((ITextPointer)position.Handle0).GetTextInRun(direction, textBuffer, startIndex, count);
        }
 
        object ITextContainer.GetAdjacentElement(StaticTextPointer position, LogicalDirection direction)
        { 
            return ((ITextPointer)position.Handle0).GetAdjacentElement(direction); 
        }
 
        DependencyObject ITextContainer.GetParent(StaticTextPointer position)
        {
            return null;
        } 

        StaticTextPointer ITextContainer.CreatePointer(StaticTextPointer position, int offset) 
        { 
            return new StaticTextPointer(this, ((ITextPointer)position.Handle0).CreatePointer(offset));
        } 

        StaticTextPointer ITextContainer.GetNextContextPosition(StaticTextPointer position, LogicalDirection direction)
        {
            return new StaticTextPointer(this, ((ITextPointer)position.Handle0).GetNextContextPosition(direction)); 
        }
 
        int ITextContainer.CompareTo(StaticTextPointer position1, StaticTextPointer position2) 
        {
            return ((ITextPointer)position1.Handle0).CompareTo((ITextPointer)position2.Handle0); 
        }

        int ITextContainer.CompareTo(StaticTextPointer position1, ITextPointer position2)
        { 
            return ((ITextPointer)position1.Handle0).CompareTo(position2);
        } 
 
        object ITextContainer.GetValue(StaticTextPointer position, DependencyProperty formattingProperty)
        { 
            return ((ITextPointer)position.Handle0).GetValue(formattingProperty);
        }

        #endregion Public Methods 

        //-------------------------------------------------------------------- 
        // 
        // Public Properties
        // 
        //---------------------------------------------------------------------

        #region Public Properties
 
        /// 
        ///  
        ///  
        bool ITextContainer.IsReadOnly
        { 
            get
            {
                return true;
            } 
        }
 
        ///  
        /// 
        ///  
        ITextPointer ITextContainer.Start
        {
            get
            { 
                Debug.Assert(_start != null);
                return _start; 
            } 
        }
 

        /// 
        /// 
        ///  
        ITextPointer ITextContainer.End
        { 
            get 
            {
                Debug.Assert(_end != null); 
                return _end;
            }
        }
 
        /// 
        /// Autoincremented counter of content changes in this TextContainer 
        ///  
        uint ITextContainer.Generation
        { 
            get
            {
                // For read-only content, return some constant value.
                return 0; 
            }
        } 
 
        /// 
        /// Collection of highlights applied to TextContainer content. 
        /// 
        Highlights ITextContainer.Highlights
        {
            get 
            {
                //agurcan: The following line makes it hard to use debugger on FDS code so I'm commenting it out 
                //Debug.Assert(false, "Unexpected Highlights access on NullTextContainer!"); 
                return null;
            } 
        }

        /// 
        ///  
        /// 
        DependencyObject ITextContainer.Parent 
        { 
            get { return null; }
        } 

        // Optional text selection, always null for this ITextContainer.
        ITextSelection ITextContainer.TextSelection
        { 
            get { return null; }
            set { Invariant.Assert(false, "NullTextContainer is never associated with a TextEditor/TextSelection!"); } 
        } 

        // Optional undo manager, always null for this ITextContainer. 
        UndoManager ITextContainer.UndoManager { get { return null; } }

        //

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