Do I need to set these variables to nil in viewDidLoad as I have in this code?

Question

- (void)viewDidUnload {
  self.GPSArray = nil;
  self.accelerometerArray = nil;
  self.headingArray = nil;
  self.managedObjectContext = nil;
  self.locationManager = nil;
  self.pointLabel = nil;
  self.accelerometerLabel= nil;
  self.headingLabel= nil;
  self.startStop = nil;
  self.lastAccelerometerReading = nil;
  self.lastGPSReading = nil;
  self.lastHeadingReading = nil;
}


- (void)dealloc {
  [GPSArray release];
  [accelerometerArray release];
  [headingArray release];
  [managedObjectContext release];
  [locationManager release];
  [pointLabel release];
  [accelerometerLabel release];
  [headingLabel release];
  [startStop release];
  [lastAccelerometerReading release];
  [lastGPSReading release];
  [lastHeadingReading release];
  [super dealloc];  
}

Answer 1

You don't have to, and if you run this, you'll be wasting some substantial execution time. Using the property method to set a property to nil is the same thing as releasing the property, with the caveat that some extra stuff may or may not happen, depending on how you've set up the setter methods.

So let's walk through this code. At the end of your viewDidUnload method, all of your properties are now nil. The object is then deallocated, and your object attempts to release a dozen nil objects or so. Now, the Objective-C runtime is pretty smart, and if you send a message to nil, (surprise surprise) nothing will happen.

So you've basically got a dozen lines that do absolutely nothing.

Answer 2

no, you shouldn't.

if you do as if the above code, you are wasting effort.

By setting them to nil in viewDidUnload, they will be going thru a process of release and retain automatically, which means, by the time the code get to dealloc, they are actually released and nil, and you are doing another release there for the nil. Releasing nil object might be erratic.

So, ignore those in viewDidUnload.

Answer 3

The reason viewDidUnload is called, is that your view is being released and any view resources should be freed.

So, you only need to free view related items.

In your case it looks like you'd only need to free the UILabels that are probably in your view. If they were marked as IBOutlets and not in assign properties, you'd want to release the memory used by them:

self.pointLabel = nil;
self.accelerometerLabel= nil;
self.headingLabel= nil;

That also means, that in viewDidLoad if you are setting up the other properties you want to make sure they are not being allocated again if they are there already as it can be called again if the view is unloaded and then reloaded again.

The reason this would be called is if the view controller received a memory warning. You can test this memory warning in the simulator to see how viewDidUnload and viewDidLoad are called.