UILabel setText doesn't work in viewWillAppear - iphone

Question

In a ViewController I have the following:
- (void)viewWillAppear:(BOOL)animated
{
DataObject *theDataObject = [self theAppDataObject];
NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
[formatter setDateFormat:#"MMM dd, yyyy HH:mm"];
NSString *dateStr = [formatter stringFromDate:theDataObject.deadline];
NSLog(#"Logged dateStr: %#", dateStr);
[dateTimeLabel setText:dateStr];
[super viewWillAppear:animated];
}
To clarify: dateTimeLabel IS wired up in the xib file. The viewWillAppear method is explicitly called from another ViewController, and is firing, like so:
- (IBAction)setDateTimeButtonClicked:(id)sender
{
DataObject *theDataObject = [self theAppDataObject];
theDataObject.deadline = [datePicker date];
FirstMobileViewController *mobileVC = [[FirstMobileViewController alloc] init];
[mobileVC viewWillAppear:YES];
[mobileVC release];
[UIView transitionWithView:self.view.superview
duration:0.5
options:UIViewAnimationOptionTransitionFlipFromRight | UIViewAnimationOptionLayoutSubviews | UIViewAnimationOptionAllowAnimatedContent
animations:^{[self.view removeFromSuperview];}
completion:NULL];
}
The viewWillAppear method is firing -- the dateStr is logged by NSLog appropriately when the superview is shown again. But the dateTimeLabel never updates. Obviously, commenting the NSLog line doesn't make a difference.
The MADDENING thing is that even though NSLog logs dateStr just fine, if I change dateStr to, say, #"Yo!" or even to a locally initialized string, then dateTimeLabel will update, no problem.
What am I missing here?

Answer 1

You method to add a child view controller isn't correct. Try with the following code (with your method, when you call ViewWillAppear, think that the view of the view controller isn't yet initialized. (you san check that with a simple hack: adding mobileVC.view; just after the mobileVC initialization)
- (IBAction)setDateTimeButtonClicked:(id)sender {
DataObject *theDataObject = [self theAppDataObject];
theDataObject.deadline = [datePicker date];
FirstMobileViewController *mobileVC = [[FirstMobileViewController alloc] init];
[self addChildViewController:mobileVC];
UIView *superView = self.view.superview;
mobileVC.view.frame = superView.bounds;
[UIView transitionWithView:superview
duration:0.5
options:UIViewAnimationOptionTransitionFlipFromRight | UIViewAnimationOptionLayoutSubviews | UIViewAnimationOptionAllowAnimatedContent
animations:^{[self.view removeFromSuperview];
[superview addSubView:mobileVC.view]}
completion:^(BOOL finished) {
[mobileVC didMoveToParentViewController:self];
}];
}
With this method, the viewWillAppear should be called automatically.

Answer 2

Firstly, you're releasing mobileVC before doing anything with it, so while it runs the code in the viewWillAppear: method, that's all that happens.
You're also not loading the XIB file for mobileVC, since you only alloc and init it. Therefore the objects you reference within viewWillAppear most likely don't exist at the point that you explicitly call the method.
You haven't shown the code that you use to present the mobileVC so it's hard to guess what the fix will be, or to understand the quirky problem you're having with string literals working. But, suffice to say, when you present the new view controller, it will be a different instance than the one you explicitly called.
Possible fix:
Use initWithNibName:bundle: instead of plain init to ensure that your XIB is loaded. Then pass mobileVC into the completion block of your transition to present it?

Answer 3

Put [super viewWillAppear:animated] at the beginning of viewWillAppear.
Maybe you never connect dateTimeLabel in xib to dateTimeLabel.
Try to use [self. dateTimeLabel setText: dateStr]