Question

i’m clicking on a row in a table and going to a new view, in the viewdidload i’m taking the nav.title and putting it in a url to send to a php page. However the url is sending before the nav.title is initialised, so i’m receiving null back from php. How do i make sure the nav.title is initialised before viewdidload, or can someone think of a better way to structure this code? thanks

Answer 1

The viewDidLoad method is in UIViewController. Something I find tricky with view controllers is that sometimes you instantiate them in code, and sometimes you instantiate them from a NIB-file.

These two paths of instantiation do not share a common method for proper initialization. So I have taken into practice to alway implement all my UIViewController subclasses using a patter like this:

- (void)primitiveInit {
    // Here I setup all my instance variables.
}

// Designated initializer for instantiating in code.
- (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)nibBundle {
    self = [super initWithNibName:nibName bundle:nibBundle];
    if (self) {
        [self primitiveInit];
    }
    return self;
}

// Always called when instantiated from NIB.
- (void)awakeFromNib {
    [super awakeFromNib];
    [self primitiveInit];
}

This way I can always trust primitiveInit to be called on my view controller before they are displayed on screen, and receive any external events.

What I have done is actually that I have added a category on NSObject that calls primitiveInit from both the root class init method, and from the root class awakeFromNib method. This way I only need to implement primitiveInit in any of my classes and never care of how they are instantiated. But this is slightly more advanced, explaining how it works is a topic on it’s own.

@implementation NSObject (CWPrimitiveInit)

+ (void)load {
    Method m1 = class_getInstanceMethod(self, @selector(init));
    Method m2 = class_getInstanceMethod(self, @selector(cw_init));
    method_exchangeImplementations(m1, m2);
    m1 = class_getInstanceMethod(self, @selector(awakeFromNib));
    m2 = class_getInstanceMethod(self, @selector(cw_awakeFromNib));
    method_exchangeImplementations(m1, m2);
}

- (void)primitiveInit {
}

- (id)cw_init {
    self = [self cw_init];
    [self primitiveInit];
    return self;
}

- (void)cw_awakeFromNib {
    [self cw_awakeFromNib];
    [self primitiveInit];
}

@end