Chinese have to learn standard Chinese, Mandarin. It's unnecessary to learn Shanghainés and Cantonés, except for some people who want to develop a closer relationship with local people. Anyway, managing a dialect makes it easier to communicate with local people, but a dialect is useless outside its specific area.

Hello Sara, Exactly! It is better to learn Mandarin ,because most people who speak originally Shanghainese and Cantonese already speak Mandarin, they would be able to understand you, yet not everyone speaks the dialects of Shanghainese and Cantonese.

Shanghaines and Cantones are just dialects,and can be only used in some place of China. While Mandarin is the common language,you can used it all over China

Shanghainese and Cantonese are dialects. Mandarin is the national language, nowaday every schools in China are using Mandarin in teaching Chinese.