TextMarkers/Segments and deletion

[DoctorVanGogh]

I've been playing around with the TextMarker example from https://github.com/siegfriedpammer/AvalonEditSamples and have encountered a problem when the text underpinning a marker is removed from the editor.

Basically I can capture a TextSegment's OnSegmentChanged and use that to remove the segment if it has been reduced to zero length. This works fine if the text edit is performed from within the segment's bounds:

If however the entire segment's contents are deleted (via a selection which encompasses the segment and more), a zero length marker will stay.:

The segment disappears from the appropriate TextSegmentCollection (markers is empty in https://github.com/siegfriedpammer/AvalonEditSamples/blob/bd6858eed774743b92d971b179b3bd3bb32655e7/TextMarkerSample/SharpDevelop/TextMarkerService.cs#L95) only to reappear during a subsequent Redraw (markers is no longer empty in https://github.com/siegfriedpammer/AvalonEditSamples/blob/bd6858eed774743b92d971b179b3bd3bb32655e7/TextMarkerSample/SharpDevelop/TextMarkerService.cs#L123).

How do I catch the second case?

[siegfriedpammer]

As far as I can remember the TextMarker was not meant to be deletable by document edits. In our past use-cases (in https://github.com/icsharpcode/SharpDevelop, where I would recommend you to take a look, if you wonder how to use a certain feature of AvalonEdit...) it was always some external event (e.g. parser updates, refreshing the list of errors by re-running the build) that caused text markers to be removed from the view. The API that's meant to be used for use-cases like this is ITextAnchor.

I won't comment on any of your suggestions in #331 because

AvalonEdit/ICSharpCode.AvalonEdit/Document/TextSegmentCollection.cs

Lines 55 to 56 in 47f61e9

	// WARNING: you need to understand interval trees (the version with the augmented 'high'/'max' field)
	// and how the TextAnchorTree works before you have any chance of understanding this code.

definitely does not apply to me ;-), so I will leave that to @dgrunwald.

Nonetheless, I hope this helps!

[dgrunwald]

SharpDevelop's TextMarker was meant for highlighting provided by external sources (e.g. compiler errors).
If you are trying to build a rich text editor, look into AvalonEdit's RichTextModel+RichTextColorizer classes instead.