Brazil is a place where you must always be aware of your surroundings, reading the street and following your gut feeling. For Brazilians, it becomes second nature, so you as a visitor may not notice.
There's an economic crisis and a new, right-wing president trying to impose his thinking, both of which have repercussions.
As a tourist, you will not have cause to be in the neighborhoods where most crime occurs, or where there is frequent unrest between police and drug dealers.. Tourists may encounter opportunistic crime like 'snatch and run', so do not carry anything that gives thieves that opportunity, and secure well any possessions you do carry with you (i.e. don't stick your arm out to take a photo with your cell phone without noticing the kid on the bike who could swoop by and grab it). Don't walk into deserted areas; common sense. The occasional unlucky, heedless, or particularly unprepared tourist may stumble into a worse situation, but it is an exception IMO. It does make for exciting headlines though, so the media fixates on these incidents. Don't take anything to Brazil that you can't afford, financially or emotionally, to give up easily in a nanosecond, though, in such an unlikely case.
That said, I have spent considerable time all over Brazil for the last 20 years and have had no problems. Once you get your feet on the ground, you will likely be surprised at how unlike the lurid media descriptions the reality is.
I have no doubt you will enjoy your trip to Rio and be planning the next visit before you even depart.