feed on feeds - 2016/09/22 - items 0 to 15

Stephen Hawking is again reminding people that perhaps shouting about our existence to aliens is not the right way to go about it, especially if those aliens are more technologically advanced. In his new half-hour program dubbed, Stephen Hawking's Favorite Places, the theoretical physicist and cosmologist said (via CNET):"If intelligent life has evolved (on Gliese 832c), we should be able to hear it," he says while hovering over the exoplanet in the animated "U.S.S. Hawking." "One day we might receive a signal from a planet like this, but we should be wary of answering back. Meeting an advanced civilization could be like Native Americans encountering Columbus. That didn't turn out so well." Hawking manages to be both worried about exposing our civilization to aliens and excited about finding them. He supports not only Breakthrough: Listen, but also Breakthrough: Starshot, another initiative that aims to send tiny nanocraft to our closest neighboring star system, which was recently found to have an Earth-like planet.

Notification block

An NSNotification observer was set up using a block — which is something I myself don’t do, since it litters an init or viewDidLoad with extraneous code and since it’s dangerous.

It’s dangerous because, unless you remember to be careful, it can capture a strong reference to self, and then that object is never going to go away. I don’t like APIs that require the developer to remember extra things like this.

And, sure enough, this was one of those cases.

The tipoff was in the memory graph debugger: the reference was labelled as “capture,” which let me know there was a block doing a capture, and it was then pretty quick to find out where.

(See also, from 2015: How Not to Crash #3: NSNotification.)

View controller / view retain cycle

There’s a general rule of programming that says objects should know about their children but not about their parents.

However, sometimes a view needs to know about its view controller. This is less than ideal, but sometimes it’s the least-bad option. (Well… I’m skeptical — but it happens, and we ship great apps, so there ya go.)

The related rule of programming says that if a child knows about its parent, it still can’t hold a strong reference to its parent.

That’s what was happening here: a view was retaining its view controller. The simple fix was to make that a weak property.

And, again, the memory graph debugger took me right to this. I could see what was happening inside the app in a way I never could before.

It’s marvelous. You should use it.

Architect David Adjaye explains his inspiration behind the new National Museum of African American History and Culture.