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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.
//
// Description: IEnumerator for TextRange and TextElement content.
//
//
using MS.Internal;
#pragma warning disable 1634, 1691 // suppressing PreSharp warnings
namespace System.Windows.Documents
{
internal class TextElementEnumerator<TextElementType> : IEnumerator<TextElementType> where TextElementType : TextElement
{
//------------------------------------------------------
//
// Constructors
//
//------------------------------------------------------
#region Constructors
// Creates an enumerator instance.
// Null start/end creates an empty enumerator.
internal TextElementEnumerator(TextPointer start, TextPointer end)
{
Invariant.Assert(start != null && end != null || start == null && end == null, "If start is null end should be null!");
_start = start;
_end = end;
// Remember what generation the backing store was in when we started,
// so we can throw if this enumerator is accessed after content has
// changed.
if (_start != null)
{
_generation = _start.TextContainer.Generation;
}
}
#endregion Constructors
//------------------------------------------------------
//
// Public Methods
//
//------------------------------------------------------
#region Public Methods
public void Dispose()
{
// Empty the enumerator
_current = null;
_navigator = null;
GC.SuppressFinalize(this);
}
object System.Collections.IEnumerator.Current
{
get
{
return this.Current;
}
}
/// <summary>
/// Return the current object this enumerator is pointing to. This is
/// generally a FrameworkElement, TextElement, an embedded
/// object, or Text content.
/// </summary>
/// <remarks>
/// According to the IEnumerator spec, the Current property keeps
/// the element even after the content has been modified
/// (even if the current element has been deleted from the collection).
/// This is unlike to Reset or MoveNext which throw after any content change.
/// </remarks>
public TextElementType Current
{
get
{
if (_navigator == null)
{
#pragma warning suppress 6503 // IEnumerator.Current is documented to throw this exception
throw new InvalidOperationException(SR.EnumeratorNotStarted);
}
if (_current == null)
{
#pragma warning suppress 6503 // IEnumerator.Current is documented to throw this exception
throw new InvalidOperationException(SR.EnumeratorReachedEnd);
}
return _current;
}
}
/// <summary>
/// Advance the enumerator to the next object in the range. Return true if content
/// was found.
/// </summary>
public bool MoveNext()
{
// Throw if the tree has been modified since this enumerator was created.
if (_start != null && _generation != _start.TextContainer.Generation)
{
throw new InvalidOperationException(SR.EnumeratorVersionChanged);
}
// Return false if the collection is empty
if (_start == null || _start.CompareTo(_end) == 0)
{
return false;
}
// Return false if the navigator reached the end of the collection
if (_navigator != null && _navigator.CompareTo(_end) >= 0)
{
return false;
}
// Advance the navigator
if (_navigator == null)
{
// Set it to the first element for the very first move
_navigator = new TextPointer(_start);
_navigator.MoveToNextContextPosition(LogicalDirection.Forward);
}
else
{
// Move to the next element in the collection
Invariant.Assert(_navigator.GetPointerContext(LogicalDirection.Backward) == TextPointerContext.ElementStart,
"Unexpected run type in TextElementEnumerator");
_navigator.MoveToElementEdge(ElementEdge.AfterEnd);
_navigator.MoveToNextContextPosition(LogicalDirection.Forward);
}
// Update current cache
if (_navigator.CompareTo(_end) < 0)
{
_current = (TextElementType)_navigator.Parent;
}
else
{
_current = null;
}
// Return true if the content was found
return (_current != null);
}
/// <summary>
/// Reset the enumerator to the start of the range.
/// </summary>
public void Reset()
{
// Throw if the tree has been modified since this enumerator was created.
if (_start != null && _generation != _start.TextContainer.Generation)
{
throw new InvalidOperationException(SR.EnumeratorVersionChanged);
}
_navigator = null;
_current = null;
}
#endregion Public Methods
//------------------------------------------------------
//
// Public Properties
//
//------------------------------------------------------
#region Public Properties
#endregion Public Properties
//------------------------------------------------------
//
// Public Events
//
//------------------------------------------------------
#region Public Events
#endregion Public Events
//------------------------------------------------------
//
// Protected Methods
//
//------------------------------------------------------
#region Protected Methods
#endregion Protected Events
//------------------------------------------------------
//
// Internal Methods
//
//------------------------------------------------------
#region Internal Methods
#endregion Internal methods
//------------------------------------------------------
//
// Internal Properties
//
//------------------------------------------------------
#region Internal Properties
#endregion Internal Properties
//------------------------------------------------------
//
// Internal Events
//
//------------------------------------------------------
#region Internal Events
#endregion Internal Events
//------------------------------------------------------
//
// Private Properties
//
//------------------------------------------------------
#region Private Properties
#endregion Private Properties
//------------------------------------------------------
//
// Private Fields
//
//------------------------------------------------------
#region Private Fields
// Edges of the span to enumerator over.
private readonly TextPointer _start;
private readonly TextPointer _end;
// Backing store generation when this enumerator was created.
private readonly uint _generation;
// Current position in the enumeration.
private TextPointer _navigator;
// Calculated content at the current position.
private TextElementType _current;
#endregion Private Fields
}
}
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