HorizontalScrollBar cannot be used when Qliveview switches from IconMode to ListMode.

My project requires QListView to switch between ListMode and IconMode using setViewMode. When it is in ListMode, I have override sizeHint, which can show horizontalScrollBar. But when I switch back from IconMode to ListMode, no matter how I do the horizontalScrollBar, it won't be show. I used setHorizontalScrollBarPolicy (Qt:: ScrollBarAlwaysOn) to make the horizontalScrollBar appear, it still looks unusable.How to make HorizontalScrollBar enabled.
1.horizontalScrollBar show

2.set IconMode

3.and switch ListMode the horizontalScrollBar looks unusable.