Advanced Mac OS X Programming: The Big Nerd Ranch Guide

Block Retain Cycles

Blocks have retain counts. If you have retain counts, you can get retain cycles. Here is a typedef for a simple block, and a class that references the block, along with a string instance variable.

t​y​p​e​d​e​f​ ​v​o​i​d​ ​(​^​B​o​r​i​n​g​B​l​o​c​k​)​(​v​o​i​d​)​;​

/​/​ ​T​h​e​ ​l​e​a​k​y​ ​o​b​j​e​c​t​.​
@​i​n​t​e​r​f​a​c​e​ ​L​e​a​k​z​o​r​ ​:​ ​N​S​O​b​j​e​c​t​ ​{​
 ​ ​ ​ ​N​S​S​t​r​i​n​g​ ​*​_​s​t​r​i​n​g​;​
 ​ ​ ​ ​B​o​r​i​n​g​B​l​o​c​k​ ​_​b​l​o​c​k​h​e​a​d​;​
}​

/​/​ ​P​r​i​n​t​ ​|​s​t​r​i​n​g​|​.​
-​ ​(​v​o​i​d​)​ ​f​u​n​k​;​

@​e​n​d​ ​/​/​ ​L​e​a​k​z​o​r​

And here are -init and -dealloc.

-​ ​(​i​d​)​ ​i​n​i​t​ ​{​ ​ ​ ​ ​i​f​ ​(​(​s​e​l​f​ ​=​ ​[​s​u​p​e​r​ ​i​n​i​t​]​)​)​ ​{​ ​ ​ ​ ​ ​ ​ ​ ​_​s​t​r​i​n​g​ ​=​ ​@​"​s​n​o​r​k​"​;​ ...