Question

I have been wondering which is the best way to load a navigation view. I have found that there are 3 ways I can do it without having major errors

What I was wondering is which one is best for memory and as a recommended practice ??

1)
no declaration in .h file (the code below IS NOT writen in the .h file)

@interface companyViewController : UIViewController {  
    EmployeeViewController *employeeDetailViewController;  
}  
@property (nonatomic, retain) EmployeeViewController *employeeDetailViewController;  

then no @syntesize in .m file, no release in dealloc and no nil in viewDidUnload and when I call the new view I do:

EmployeeViewController *employeeController = [[EmployeeViewController alloc]  
      initWithNibName:@"EmployeeViewController" bundle:nil];  

[self.navigationController pushViewController:employeeController animated:YES];  
[employeeController release];  

2)
I create it in the .h file (the code below IS written in the .h file)

@interface companyViewController : UIViewController {  
    EmployeeViewController *employeeDetailViewController;  
}  
@property (nonatomic, retain) EmployeeViewController *employeeDetailViewController;  

then I @syntesize in .m file, with a release in dealloc and a nil in viewDidUnload and when I call the new view I do:

EmployeeViewController *employeeController = [[EmployeeViewController alloc]  
      initWithNibName:@"EmployeeViewController" bundle:nil];  

employeeDetailViewController = employeeController;  

[self.navigationController pushViewController:employeeController animated:YES];  
[employeeController release];  

3)
I do like 2 but I call the new view like this

employeeDetailViewController = [[EmployeeViewController alloc]  
      initWithNibName:@"EmployeeViewController" bundle:nil];  

[self.navigationController pushViewController:employeeController animated:YES];  

I feel like #3 is wrong because from what I understand in the memory management, I allocate it once in the @property (nonatmoic, retain) and I also retain it when I alloc it when I decide to call it. This will make the view have a retain count of 1 and lead to leaks.

To make sure I do not create an excessive amount of new views and get EXC_BAD_ACCESS or memory leaks, which one should be best ?

Thanks for the help

Answer 1

In none of these examples are you actually using the property you declare. I’ll go through them in turn.

1. You created a property called employeeDetailViewController, but you never synthesize it or store anything in it. Your view controller is only ever stored in a local variable before passing it off to the navigation controller.

2. You create an instance variable called employeeDetailViewController, and a property also called employeeDetailViewController. However, you never store anything in the property, you only access the instance variable directly. Since you don’t retain the view controller (it doesn’t happen automatically when you use instance variables), you’ve got a situation where you might over-release.

3. This one will actually crash. You told it to pushViewController:employeeController without having defined employeeController.

So, let’s consider what’s right. There are two issues here: firstly, how to use properties, and secondly, whether you need an instance variable/property to refer to the view controller at all.

Considering properties:

To access a property, you use self.propertyName. If you just use propertyName directly, you’re writing directly into the instance variable, and the memory management stuff (like automatically retaining stuff that’s put in the property) is completely bypassed. Generally, you should only ever do that in your init or dealloc method: everywhere else you should access the property properly by self.propertyName.

Do you need an instance variable/property for the view controller?

I would say you don’t actually need an instance variable or property for the view controller you’re pushing. Once it’s been handed off to the navigation controller, in general you won’t need to access it again. My version of your code would be:

aViewController = [[EmployeeViewController alloc]  
      initWithNibName:@"EmployeeViewController" bundle:nil];  

[self.navigationController pushViewController:aViewController animated:YES];

Unless you’re wanting to refer to that particular view controller from elsewhere in your code, this is all you need. Nothing in the header, no property anywhere.