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TextBoxView: fix crash during large selection with pending background layout #11461

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TextBoxView: fix crash during large selection with pending background layout #11461

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27 changes: 18 additions & 9 deletions src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/documents/TextBoxView.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -576,7 +576,6 @@ Rect ITextView.GetRectangleFromTextPosition(ITextPointer position)
Rect rect;

Invariant.Assert(this.IsLayoutValid);
Invariant.Assert(Contains(position));

int offset = position.Offset;
if (offset > 0 && position.LogicalDirection == LogicalDirection.Backward)
Expand Down Expand Up @@ -717,7 +716,6 @@ Geometry ITextView.GetTightBoundingGeometryFromTextPositions(ITextPointer startP
ITextPointer ITextView.GetPositionAtNextLine(ITextPointer position, double suggestedX, int count, out double newSuggestedX, out int linesMoved)
{
Invariant.Assert(this.IsLayoutValid);
Invariant.Assert(Contains(position));

newSuggestedX = suggestedX;
int lineIndex = GetLineIndexFromPosition(position);
Expand Down Expand Up @@ -764,7 +762,6 @@ ITextPointer ITextView.GetPositionAtNextPage(ITextPointer position, Point sugges
bool ITextView.IsAtCaretUnitBoundary(ITextPointer position)
{
Invariant.Assert(this.IsLayoutValid);
Invariant.Assert(Contains(position));
bool boundary = false;

int lineIndex = GetLineIndexFromPosition(position);
Expand Down Expand Up @@ -803,7 +800,6 @@ bool ITextView.IsAtCaretUnitBoundary(ITextPointer position)
ITextPointer ITextView.GetNextCaretUnitPosition(ITextPointer position, LogicalDirection direction)
{
Invariant.Assert(this.IsLayoutValid);
Invariant.Assert(Contains(position));

// Special case document start/end.
if (position.Offset == 0 && direction == LogicalDirection.Backward)
Expand Down Expand Up @@ -880,7 +876,6 @@ ITextPointer ITextView.GetNextCaretUnitPosition(ITextPointer position, LogicalDi
ITextPointer ITextView.GetBackspaceCaretUnitPosition(ITextPointer position)
{
Invariant.Assert(this.IsLayoutValid);
Invariant.Assert(Contains(position));

// Special case document start.
if (position.Offset == 0)
Expand Down Expand Up @@ -928,7 +923,6 @@ ITextPointer ITextView.GetBackspaceCaretUnitPosition(ITextPointer position)
TextSegment ITextView.GetLineRange(ITextPointer position)
{
Invariant.Assert(this.IsLayoutValid);
Invariant.Assert(Contains(position));

int lineIndex = GetLineIndexFromPosition(position);

Expand Down Expand Up @@ -1124,20 +1118,35 @@ internal void Rerender()
// Returns the index of the line containing the specified offset.
// Offset has forward direction -- we always return the following
// line in ambiguous cases.
//
// When background layout is pending, offsets beyond the measured region
// are clamped to the last measured line to prevent crashes during
// incremental layout operations (e.g., text selection highlighting).
internal int GetLineIndexFromOffset(int offset)
{
int index = -1;
int min = 0;
int max = _lineMetrics.Count;
int lastIndex = max - 1;
Invariant.Assert(lastIndex >= 0);

Invariant.Assert(_lineMetrics.Count >= 1);
// Defensive: If offset is beyond what we've measured during background layout,
// clamp to last line. This is expected behavior when large text selections occur
// before layout completes, similar to the behavior in GetLineIndexFromPoint and GetVisibleLines methods.
LineRecord record = _lineMetrics[lastIndex];
if (offset > record.EndOffset)
{
// This should only happen during background layout
Invariant.Assert(IsBackgroundLayoutPending);
return lastIndex;
}

while (true)
{
Invariant.Assert(min < max, "Couldn't find offset!");

index = min + (max - min) / 2;
LineRecord record = _lineMetrics[index];
record = _lineMetrics[index];

if (offset < record.Offset)
{
Expand All @@ -1149,7 +1158,7 @@ internal int GetLineIndexFromOffset(int offset)
}
else
{
if (offset == record.EndOffset && index < _lineMetrics.Count - 1)
if (offset == record.EndOffset && index < lastIndex)
{
// Go to the next line if we're between two lines.
index++;
Expand Down