Memory Management, ARC - what to nil?

Question

Background -

I am using automatic reference counting on a project. The root view is a Table View (Master / Detail setup) showing a list of "slide shows". Click on a table cell and you are taken to the detail view which consists of a Scroll view with views (viewController.view) in it (this is the "slide show"). Each slide show has a front cover and back cover (same view controller formatted differently) that sandwich an variable number of pages. Here is the code to load the slide show:

- (void)loadScrollView
{    
// The front and back cover are set in Interface Builder because they
// are reused for every slide show, just labels are changed.
[self.scrollView addSubview:self.frontCoverViewController.view];
[self.frontCoverViewController setCoverTitle:_data.name creationDate:_data.creationDate isFrontCover:YES];
[self.pagesArray addObject:self.frontCoverViewController];

for (int i = 0; i < [self getTotalNumberOfComps]; i++) 
{
    PageViewController *pageView = [[PageViewController alloc] init];
    pageView.data = [_compsArray objectAtIndex:i];

    [_scrollView addSubview:pageView.view];
    pageView.data.imgView = pageView.imageView;
    pageView.slideShowViewController = self;
    [_pagesArray addObject:pageView];
}

[self.scrollView addSubview:self.backCoverViewController.view];
[self.backCoverViewController setCoverTitle:_data.name creationDate:_data.creationDate isFrontCover:NO];
[self.pagesArray addObject:self.backCoverViewController];

[self.scrollView bringSubviewToFront:_frontCoverViewController.view];
[self setCurrentPage:0];
}

Problem -

So Im trying to reuse this slide show view controller so I need to nil and recreate the pages in the middle because each slide show has a different number of slides. Note a slide [PageViewController] is just a view with an ImageView in it. It has more functionality so we need the controller however the main display of the VC is the ImageView. I have created the following method to "empty" the slide show before running loadScrollView again with new data. Here is the empty method:

- (void)saflyEmptyScrollView
{
for (int i = 0; i < [self.pagesArray count]; i++) 
{
    if (i == 0 && i == ([self.pagesArray count]-1)) {
        CoverViewController *cover = (CoverViewController*)[self.pagesArray objectAtIndex:i];
        [cover.view removeFromSuperview]; 
    } else {
        PageViewController *page = (PageViewController*)[self.pagesArray objectAtIndex:i];
        [page.view removeFromSuperview];
        page = nil;
    }
}
self.pagesArray = nil;
self.pagesArray = [[NSMutableArray alloc] init];
} 

Big Question -

My main question is do I need to set the ImageView of each of these pages to nil? Or does setting the page itself to nil also free up the memory used by the ImageView/Labels/etc that are used in that view controller?

I tried adding self.imageView = nil; to the PageViewController's viewDidUnload and viewWillUnload methods (one at a time not in both) and I realized that setting page = nil does not call the pages Unload methods. Am I freeing up memory correctly.

I've read a lot of articles but Im still not sure if Im managing memory in the best way possible. Thanks so much for the help!

Answer 1

Generally, you shouldn't have to set things to nil. And in this specific case, the setting things to nil is doing nothing.

The line page = nil; is redundant, because the variable page goes out of scope immediately afterwards anyway. ARC knows this and doesn't need you to set it to nil.

And self.pagesArray = nil; is redundant because you follow it with self.pagesArray = [[NSMutableArray alloc] init]; . The second line on its own will suffice.