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When my view controller is first presented, I want it to potentially update a cache that provides the data for that view. However, when the user taps the back button from a deeper view controller to return to this view controller, I don't want to update the cache again.

Which event should I be using?

  • in init, I don't have all the parameters I need yet.
  • viewWillAppear will be fired every time the view will appear.
  • viewDidLoad will be fired every time the view has been loaded from the nib, which I believe could happen a second time if there's a memory warning. (Or is this wrong?) Since this is not a memory resident cache, it seems the wrong place to handle this.
  • having the caller call something extra is inelegant, if there's a built-in way to handle this.

To clarify, this is not a memory resident cache. This is parsing an XML file to binary. The binary is loaded and unloaded in viewDidLoad and viewDidUnload. This is a prerequisite for that step, making sure the binary is up-to-date prior to it being loaded.

Steven Fisher
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1 Answers1

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Using init may work, but I would recommend a simple subclass of UINavigationController. Create a new method called setRootTableViewController:(UITableViewController *)controller, or something like it. In the method implementation call this:

[controller.tableView reloadData];
[self pushViewController:controller animated:NO];

reloadData will call all of your delegate and data source methods, and use them to update the table. If you want a special method call on your table view controller instead, you could change the method declaration to setRootTableViewController:(CustomTableViewController *)controller (or whatever your custom table controller is called), and replace the reloadData line with one that calls that method.

Then, in your app delegate, instead of creating a UINavigationController and adding your custom view controller, create one of these, and call this method to add the first view.

However, if you are using a nib to set the rootViewController, you can just override initWithRootViewController:(UIViewController *)controller, as I imagine that is what the nib will call to set the first view in the stack:

- (id)initWithRootViewController:(UIViewController *)rootViewController {
  if ((self = [super init])) {
    [(CustomController *)rootViewController doSomethingSpecial];
    [self pushViewController:rootViewController];
  }
}

Hope this helps!

aopsfan
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  • also in a 4.0+ environment, the app could go into the background for several hours before coming back to the foreground, you will likely want to notice that and reload your cache - perhaps you should set a timestamp when you reload it and base your decision on that – bshirley Sep 15 '11 at 00:48