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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//
// Enumerator class for returning descendants of TextBlock and FlowDocumentPage
//
using System.Collections;
using System.Collections.ObjectModel;
#pragma warning disable 1634, 1691 // suppressing PreSharp warnings
namespace System.Windows.Documents
{
/// <summary>
/// Enumerator class for implementation of IContentHost on TextBlock and FlowDocumentPage.
/// Used to iterate through descendants of the content host
/// </summary>
internal class HostedElements : IEnumerator<IInputElement>
{
//-------------------------------------------------------------------
//
// Constructors
//
//-------------------------------------------------------------------
#region Constructors
internal HostedElements(ReadOnlyCollection<TextSegment> textSegments)
{
_textSegments = textSegments;
_currentPosition = null;
_currentTextSegment = 0;
}
#endregion Constructors
//-------------------------------------------------------------------
//
// IDisposable Methods
//
//-------------------------------------------------------------------
#region IDisposable Methods
void IDisposable.Dispose()
{
_textSegments = null;
GC.SuppressFinalize(this);
}
#endregion IDisposable Methods
//-------------------------------------------------------------------
//
// Private Methods
//
//-------------------------------------------------------------------
#region Private Methods
public bool MoveNext()
{
// If _textSegments has been disposed, throw exception
ObjectDisposedException.ThrowIf(_textSegments == null, typeof(HostedElements));
if (_textSegments.Count == 0)
return false;
// Verify that current position matches with current text segment, and set it if it's null.
if (_currentPosition == null)
{
// We should be at the start
Debug.Assert(_currentTextSegment == 0);
// Type check that we can create _currentPosition here
if (_textSegments[0].Start is TextPointer)
{
_currentPosition = new TextPointer(_textSegments[0].Start as TextPointer);
}
else
{
// We cannot search, return false
_currentPosition = null;
return false;
}
}
else if (_currentTextSegment < _textSegments.Count)
{
// We have not yet reached the end of the container. Assert that our position matches with
// our current text segment
Debug.Assert(((ITextPointer)_currentPosition).CompareTo(_textSegments[_currentTextSegment].Start) >= 0 &&
((ITextPointer)_currentPosition).CompareTo(_textSegments[_currentTextSegment].End) < 0);
// This means that we are in the middle of content, so the previous search would have returned
// something. We want to now move beyond that position
_currentPosition.MoveToNextContextPosition(LogicalDirection.Forward);
}
// Search strarting from the position in the current segment
while (_currentTextSegment < _textSegments.Count)
{
Debug.Assert(((ITextPointer)_currentPosition).CompareTo(_textSegments[_currentTextSegment].Start) >= 0);
while (((ITextPointer)_currentPosition).CompareTo(_textSegments[_currentTextSegment].End) < 0)
{
if (_currentPosition.GetPointerContext(LogicalDirection.Forward) == TextPointerContext.ElementStart ||
_currentPosition.GetPointerContext(LogicalDirection.Forward) == TextPointerContext.EmbeddedElement)
{
return true;
}
else
{
_currentPosition.MoveToNextContextPosition(LogicalDirection.Forward);
}
}
// We have reached the end of a segement. Update counters
_currentTextSegment++;
if (_currentTextSegment < _textSegments.Count)
{
// Move to the next segment
if (_textSegments[_currentTextSegment].Start is TextPointer)
{
_currentPosition = new TextPointer(_textSegments[_currentTextSegment].Start as TextPointer);
}
else
{
// This state is invalid, set to null and return false
_currentPosition = null;
return false;
}
}
}
// We have reached the end without finding an element. Return false.
return false;
}
#endregion Private Methods
//-------------------------------------------------------------------
//
// Private Properties
//
//-------------------------------------------------------------------
#region Private Properties
object IEnumerator.Current
{
get { return this.Current; }
}
void IEnumerator.Reset()
{
throw new NotImplementedException();
}
public IInputElement Current
{
get
{
// Disable PRESharp warning 6503: "Property get methods should not throw exceptions".
// HostedElements must throw exception if Current property is incorrectly accessed
if (_textSegments == null)
{
// Collection was modified
#pragma warning suppress 6503 // IEnumerator.Current is documented to throw this exception
throw new InvalidOperationException(SR.EnumeratorCollectionDisposed);
}
if (_currentPosition == null)
{
// Enumerator not started. Call MoveNext to see if we can move ahead
#pragma warning suppress 6503 // IEnumerator.Current is documented to throw this exception
throw new InvalidOperationException(SR.EnumeratorNotStarted);
}
IInputElement currentElement = null;
switch (_currentPosition.GetPointerContext(LogicalDirection.Forward))
{
case TextPointerContext.ElementStart:
Debug.Assert(_currentPosition.GetAdjacentElementFromOuterPosition(LogicalDirection.Forward) is IInputElement);
currentElement = _currentPosition.GetAdjacentElementFromOuterPosition(LogicalDirection.Forward);
break;
case TextPointerContext.EmbeddedElement:
Debug.Assert(_currentPosition.GetAdjacentElement(LogicalDirection.Forward) is IInputElement);
currentElement = (IInputElement)_currentPosition.GetAdjacentElement(LogicalDirection.Forward);
break;
default:
// Throw exception because this function should only be called after MoveNext, and not
// if MoveNext returns false
Debug.Assert(false, "Invalid state in HostedElements.cs");
break;
}
return currentElement;
}
}
#endregion Private Properties
//-------------------------------------------------------------------
//
// Private Fields
//
//-------------------------------------------------------------------
#region Private Fields
ReadOnlyCollection<TextSegment> _textSegments;
TextPointer _currentPosition;
int _currentTextSegment;
#endregion Private Fields
}
}
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