Question

I’m fairly new to Cocoa Touch. Right now I’m trying to subclass UIViewController to provide my custom view. Since I intend to save the content of a UITextField (passcodeField) using NSUserDefaults, I want to be notified whenever the UITextField changes its value.

I’ve read somewhere that in order to do that I should add the view controller to be an observer of the UITextFieldTextDidChangeNotification notification. However I’m just not sure when to do that. I’ve considered several options.

1. In the -loadView method. However, since I’m loading my view using a XIB, I think i shouldn’t mess with this method and should instead leave it as-is. (Am I correct on this point, BTW? )

2. In the -viewWillAppear method. But this method may be called multiple times because the view may be moved out and into the screen without being destroyed and recreated. (Am I correct? ) This will not do any harm to the program but sure doesn’t seem like the correct way.

3. In the initializer of the UIViewController. If I want to add the notification there I must reference the UITextField. By doing this I essentially cause the view to created before it is really needed. Also I think I read somewhere that if the system runs low on memory the offscreen views may be destroyed. Thus I may lose the notification observing if such thing happens, right?

So I’m totally confused right now. Could you guys give me some advice of where to put it? Thanks so much!

Answer 1

Put it in the – (void)viewDidLoad method of your ViewController remember to call [super viewDidLoad]; at the start of your implementation.