当离开INSERT模式时，Preview窗口会自动关闭
vimrc:
" If you prefer the Omni-Completion tip window to close when a selection is " made, these lines close it on movement in insert mode or when leaving " insert mode autocmd CursorMovedI * if pumvisible() == 0|pclose|endif autocmd InsertLeave * if pumvisible() == 0|pclose|endif