How to make a continuous Cell in NSOutlineView?

Question

I want to have a continuous Cell, which is not cropped to the width of the corresponding table column. Returning YES to the - (BOOL)outlineView:(NSOutlineView *)outlineView isGroupItem:(id)item delegate method takes no effect.

This screenshot visualizes my problem:

Answer 1

According to the documentation, outlineView:dataCellForTableColumn:item: will be called a first time with the table column parameter set to nil. If you return a cell in that case (as opposed to returning nil), it will be used to draw group rows.