Hi Hristo,

I’m using the ExplorerBar Style of the control.
I’m expecting this to work like the Control.Dock.Fill or TableLayoutPanel.Column.Autosize settings.
I think by other software I have never seen that behaviour combined with expandable elements.
(although Control.Dock?)

I would expect following behaviour:

The UltraExplorerBar should have a AutoSizeGroup property.
If that property is null or the associated Group is closed, the UltraExplorerBar’s behaviour should be like it is now.
If that property is one of the Group of the ExplorerBar and the Group is expanded, the behaviour should be as follow:

1.) If you make the parent window greater or you collapse a Group:
You should never show a free background area below the last Group, you should make the ContainerHeight of the AutoSizeGroup bigger instead.

2.) If you make the parent window smaller or you expand a Group:
You should never show a ScrollBar until the ContainerHeight of the AutoSizeGroup is greater than 0, you should make it smaller instead.

I think the key to the solution is in the Paint Method of the ScrollBar, you are calculating there already all the informations, what we need.

Principally the effect must be the same as you would dock all the Groups above the AutoSizeGroup to the top, and all the Groups below it to the bottom.