As a visitor from Australia I was able to use Bike sharing in Beijing through a local friend. It was an exhilarating way to get around and see the city and has truly made my journey plain, good fun. I would like to find out how tourists can independently use this system as I visited Xian by myself and would have liked the chance to cycle.
Unfortunately you have to have linked your Chinese bank card to your WeChat account in order to pay for the service (and in order to pay the deposit and verify your identity), so as of yet it doesn't seem like there is a way for tourists to use this service.