Paying the right amount for taxi in Shanghai

Oh, as I know, most formal taxies need you to pay the money after arriving at the destination.
You can see the cab fare on the screen in the front of taxi. The fare is calculate by distance first and then shown on the screen. In addition, among these taxi companies, Dazhong is the most popular one. Generally speaking, you are not asked to pay bigger amount as long as you find the formal taxi.