Datagridview cellvalidating not working
Because Not Set restores the value inheritance, the Resizable property will never return a Not Set value unless the row or column has not been added to a Data Grid View control.
Set Resizable to Not Set to restore the inheritance.
You will typically call the programmatic resizing methods at specific times.
It is also useful to provide initial sizes for user-resizable rows, columns, and headers, and for column fill mode.
The enumerations used by sizing properties and methods have similar values for content-based sizing.
The new sizes are automatically calculated to display all cell contents without clipping.