Zoom and page changed events for FlowDocumentPageViewer

Download source files - here

My old known Bala send to me this link.

Kent Boogaart has written an article that describes approach searching and highlighting text in FlowDocumentPageViewer - Search and Highlight Text in an Arbitrary Visual Tree. Unfortunate, two serious issues present there. I copy theirs description from msdn forum:

1. When I change the pages of the FlowDocumentPageViewer, my Rectangular highlighted area remains the same and it is not sinking with the Text.
2. When I zoom in or zoom out of the FlowDocumentPageViewer, the text gets zoomed but the Highlight rectangle remains in the same position.

Seems.. solution should be easy - just add DoSeach() method in PageChanged and ZoomChanged event handler methods of FlowDocumentPageViewer but it doesn't have events for notice these actions. So I decided just to implement these events :). FlowDocumentPageViewer doesn't have protected and virtual methods like OnZoomChanged or OnPageChanged. It was bad. But I found four protected and virtual methods that could help me they are OnNextPageCommand(), OnPreviousPageCommand(), OnIncreaseZoomCommand() and OnDecreaseZoomCommand(). When I added call to rise my events in theirs override methods I found that this approach wasn't work. It happened because command logic works through concurrency approach. I called the rise methods through BeginInvoke for delay the calls rise methods - and problem was solved.

You can download sources with fix above.

PS: I didn't have time for full investigate sources.. but one question. Why did Kent use SearchRectangle class? In my opinion common Rect is enough.