Question

I am having a strange issue with tableview showing (null) when another ViewController comes and goes. I traced it down to the place that it reads the data to display to the tableview and found that it read null for data. To debug this, I need to understand how memory management really works for iPhone. I used the following code in my application delegate to create an array of objects. This was from a sample code which I modified for my app. My question is when one creates an array like this, would the [tempArray release] actually release the array that was just created?

//Initialize the hardware array.
NSMutableArray *tempArray = [[NSMutableArray alloc] init];
self.hardwareArray = tempArray;
[tempArray release];

This type of code seems to be very common for iPhone. The tutorials keeps saying for example, now that you passed the data to the controller you can release it. But my C and C++ experience tells me, if you release the memory it would be gone, and if its address is sitting someplace on the stack, its no good. Is the data being copied to another place rather than address being passed?

Also when releasing memory in a set routine like the one below, should I be checking to see if the modleName is not nil before releasing it. What happens if one released modelName that is already nil?

-(void) setModelName:(NSString *)newValue {
    self.isDirty = YES;
    [modelName release];
    modelName = [newValue copy];
}

Answer 1

My question is when one creates an array like this, would the [tempArray release] actually release the array that was just created?

If the @property of the object is assign it would get released. But usually you use retain or copy as @property. And if the property is retain, the setter you call with self.hardwareArray = ... (ie [self setHardwareArray:...]) will retain the object. If the property is copy it will create a new object that is retained already.

Also when releasing memory in a set routine like the one below, should I be checking to see if the modleName is not nil before releasing it. What happens is one released modelName that is already nil?

In objective-c messages sent to nil are perfectly legal. No need to worry, no need to check for nil.
If you release an instance variable outside of dealloc you should set it to nil after releasing it.