Spain as a whole is a country featuring many diverse regions and languages. It is actually more like being in many countries rather than just one.
In Catalonia, they consider Catalan the main language. In Galicia, it is Gallego (Galician). In the Basque region, it is Euskera, and even Valencia has a ¨Lengua Valenciana¨ which is essentially Catalan (but don't tell a native of Valencia this..!) All signage such as in airports is posted first in the region's language and then in Spanish (Castellano) and then usually in English.
The intense feeling of diversity in the language is also important enough to justify studios making TV shows and movies being dubbed in all the languages. (Just got through watching an old episode of Murder She Wrote in Catalan, matter of fact, quite interesting LOL) and seperate news programs in the languages.
Even in Andalucia, they speak Spanish with a distinct different accent.
But you're totally right, the country itself's official language is Spanish which is often called ¨Castellano¨ in all regions, not just Catalonia (Barcelona). You are also right in that there is a lot of drama countrywide involving the languages but usually, as a tourist, if you go to Barcelona, for example, they will not snub you for speaking Castellano (Spanish) and not Catalan. However, if I were to go as a Spaniard, and did not make atleast a small effort to partake in some Catalan, I would get some form of cold shoulder at some point, often times by an older person.