Preventive action is still better so leave your important document, debit and credit cards locked up in your hotel safe. Secure copies of your documents and bring them with you. Bring as much cash as you need. A neck pouch is a safer spot for your valuables compared to back pocket wallets.
If you see pickpockets on the streets, be sure to take action and warn other potential victims and don’t be afraid to be loud. Avoid little, dark alleys at night and take cabs which are favorable for mid-European relations.
People in Barcelona are helpful by nature but beware also of unasked and overly obtrusive helpfulness.