dotnet
Replace boxing IList in HighlightChangedEventArgs and seal derived classes
Description
The Ranges property on the internal class HighlightChangedEventArgs was declared as an IList, but was always backed by an instance of ReadOnlyList<TextSegment>. Retrieving a list of text segments would thus always box an instance of the TextSegment struct. I've changed this property to declare it as an IList<TextSegment>.
I also swapped an ArrayList with a List<int> in FixedDocument.cs, which stored a list of page numbers.
Finally, I marked all the five classes derived from HighlightChangedEventArgs as sealed. All fives of these classes were private, so there's no API surface change here.
Customer Impact
Reduced memory usage/GC pressure.
Regression
No.
Testing
Local build and tests, sample application runs.
Risk
Low. The Ranges property is only read by DocumentSequenceTextContainer, FixedDocument and FlowDocument. In all three locations, it's indexed into and the result was explicitly cast to a TextSegment.
