onFormat event works differently in preview and report view (1 Viewer)

I'm trying to make a kind of tree structure on a report for better visualization of the structure of the technology, my report describes.
For making this possible, a procedure runs through the different levels and bottom units of the record set to set booleans, like last, or first in the group etc.
After having settled this the report opens and the onFormat event sets the different branch lines visible/non visible to form the tree structure correctly.

Works fine, but only in print preview.

Surprisingly when I switch to a report view - which would be my target to handle user triggered events - the lines visibilities don't follow the booleans state. If I switch back and forth between the two views, the difference is systematically there on report view and correct in print preview.

I have no idea for the reason, can someone help?

OnFormat only works when the actual Print process is being fired. Report view doesn't use the actual print formatting.

Thanks Minty,

That makes sense.
Is there an event that would do the same job on the line visibility in the headers but in report view?

Thanks

petko