Release from zero to free memory

Question

In my root view controller, in my didReceiveMemoryWarning method, I look at a couple of data structures (which are stored in a global singleton called DataManager) and drop the hardest things that I have - one or two images, maybe twenty or thirty or more records data.

Now I go through and set them to zero. I also set a boolean flag so that the various view controllers that need this data can easily recognize for a reboot. Thusly:

DataManager *data = [DataManager sharedDataManager]; for (Event *event in data.eventList) { event.image = nil; event.thumbnail = nil; } for (WondrMark *mark in data.wondrMarks) { mark.image = nil; } [DataManager sharedDataManager].cleanedMemory = YES; 

Today I think, though ... and I'm not really sure that everything that allocates memory is really freed up when I do this. Should I use these images instead of release and possibly hit them with new alloc and init when I need them later?

Answer 1

Setting the instance variable directly, as mipadi says, does not free the object to which it refers. However, what you do is different from the others: you set the property value of the object. Depending on how this property is declared, this can really release the value it refers to. A property declared retain or copy , rather than assign , receives a synthesized access method ( setImage: method, which converts the .image = syntax), which releases its old value when setting a new one. So, in this case, if your WondrMark property WondrMark declared as retain , setting it to nil through the property, it will automatically undo the old image. If it is assign , you need to release the image before setting the property to nil.

Answer 2

Objects are not freed when you set them to nil , so yes, you have to free them.

Answer 3

You cannot directly pass instances or properties of instances of other objects. These objects themselves are responsible for this.

However, if an object can free its instance variables when setting a new one (for example, with retain parameters), then setting the instance variable to nil will cause the object to return the old value.