I used the package
beamer outer theme split numbered to make it for themes with navigation. But the theme
Hannover is different. Is re-defining the footline the only choice, or is there some other convenient way?
Update: the solutions like
can both do the job, but not so grace as I expect. Both of them will ruin the layout of Hannover. It is better to put the page number on the bottom of the left column, or at the left side of the navigation row.