I have this grid with tree columns in the WPF, The Horizontal Collapsar is a content control that I collapse its Content Presenter.
everything works good pic1 and pic2, but if I change column’s width by the grid Splitter it doesn’t work pic3.

[pic1](https://i.sstatic.net/vMzkTbo7.png)
[pic2](https://i.sstatic.net/3gECzclD.png)
[pic3](https://i.sstatic.net/pBUFgHxf.png)

I know grid Splitter changed the actual width so I set the width of Horizontal Collapsar in a trigger.
this is the my code:
Horizontal Collapsar
Main window