Question

For example, I created an array and put some custom class into it. Should I nil and release them by a certain order? If I put background ASIHTTPRequests in a array, will there be a leak if I release the array first? Is it the same in ARC? Thank you for your answers.

Answer 1

When you add an object to an NSArray it is automatically retained, then when you release the array a release signal is sent to all the objects in that array. So:

-(void)someMethod{

   NSString *newString = [[NSString alloc] initWithString:@"Hello"]; //newString retainCount = 1
   NSArray *newArray = [[NSArray alloc] initWithObjects: newString]; //newString retainCount = 2 

   [newArray release];  //newString retainCount = 1
   [newString release];  //newString retainCount = 0

} 

Is the same as:

-(void)someMethod{

   NSString *newString = [[NSString alloc] initWithString:@"Hello"]; //newString retainCount = 1
   NSArray *newArray = [[NSArray alloc] initWithObjects: newString]; //newString retainCount = 2 

   [newString release];  //newString retainCount = 1
   [newArray release];  //newString retainCount = 0

} 

In fact the 2nd code is a very common practice when you want to create an array of objects without taking care of individual references to those objects.