Callbacks and object ownership

With all of these callbacks, there is a danger that objects waiting for the callbacks might not get deallocated correctly. Thus, it was decided that:

  • Notification centers do not own their observers. If an object is an observer, it will typically remove itself from the notification center in its dealloc method:

    -​ ​(​v​o​i​d​)​d​e​a​l​l​o​c​
{​
 ​ ​ ​ ​[​[​N​S​N​o​t​i​f​i​c​a​t​i​o​n​C​e​n​t​e​r​ ​d​e​f​a​u​l​t​C​e​n​t​e​r​]​ ​r​e​m​o​v​e​O​b​s​e​r​v​e​r​:​s​e​l​f​]​;​
}​

  • Objects do not own their delegates or data sources. If you create an object that is a delegate or data source, your object should “excuse” itself in its dealloc method:

    -​ ​(​v​o​i​d​)​d​e​a​l​l​o​c​
{​
 ​ ​ ​ ​[​w​i​n​d​o​w​T​h​a​t​B​o​s​s​e​s​M​e​A​r​o​u​n​d​ ​s​e​t​D​e​l​e​g​a​t​e​:​n​i​l​]​;​
 ​ ​ ​ ​[​t​a​b​l​e​V​i​e​w​T​h​a​t​B​e​g​s​F​o​r​D​a​t​a​ ​s​e​t​D​a​t​a​S​o​u​r​c​e​:​n​i​l​]​;​
}​

  • Objects do not own their targets. If you create an object that is a target, your object should zero the target pointer in its dealloc method:

    -​ ​(​v​o​i​d​)​d​e​a​l​l​o​c​
{​
 ​ ​ ​ ​[​b​u​t​t​o​n​T​h​a​t​K​e​e​p​s​S​e​n​d​i​n​g​M​e​M​e​s​s​a​g​e​s​ ​s​e​t​T​a​r​g​e​t​:​n​i​l​]​;​
}​

None of these issues exist in this program because your Logger object will not be deallocated before the program terminates. (Also, in a bit of a fluke, in this exercise I used two well-documented exceptions to the rules: an NSURLConnection owns its delegate and an NSTimer owns its target.)

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