Issue with AutoLayout and ChildViewControllers (incorrect size of ChildVCs' view)

Question

I'm experiencing some difficulties doing a rather simple thing, I'm missing something but don't see...

I reproduced the issue with a very simple App (using IB) :

• App's main ViewController is a UINavigationController.
• NavigationController's root is "FirstViewController".
• FirstViewController and SecondViewController are empty UIViewController subclasses.
  • Their XIB files where generated by XCode when creating the classes, AutoLayout is enabled.
  • I placed Labels on top and bottom of SecondViewController (Vertical space constraints = 0).

Using ChildViewControllers

Problem is if I display SecondViewController via "ChildViewControllers" method, it goes wrong on my iPhone4: I don't see bottom label.

// In FirstViewController.m
- (IBAction)child:(id)sender {
    [self addChildViewController:self.secondVC];
    [self.view addSubview:self.secondVC.view];
    [self.secondVC didMoveToParentViewController:self];
}

Using NavigationController

If I display "SecondViewController" through the NavigationController, everything is fine, SecondViewController is displayed properly.

// In FirstViewController.m
- (IBAction)push:(id)sender {
    [self.navigationController pushViewController:self.secondVC animated:YES];
}

Also, as soon as SecondViewController has been displayed once through NavigationController, it'll be always well displayed.

I'm surely missing something, but what? :p Do you have any ideas?

I Uploaded the simple project on dropbox: https://dl.dropbox.com/u/36803737/sharebox/AutoLayoutTest.zip

Thanks!

julien

Answer 1

Your dropbox link doesn't work, so I couldn't try this out. Try setting the frame of secondVC before you add it as a subview:

secondVC.view.frame = self.view.bounds;

If you want to do it with constraints, I do it this way:

- (IBAction)child:(id)sender {
    [self addChildViewController:self.secondVC];
    [self.view addSubview:self.secondVC.view];
    [self constrainViewEqual:secondVC.view];
    [self.secondVC didMoveToParentViewController:self];
}

-(void)constrainViewEqual:(UIView *) view {
    [view setTranslatesAutoresizingMaskIntoConstraints:NO];
    NSLayoutConstraint *con1 = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeCenterX relatedBy:0 toItem:view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];
    NSLayoutConstraint *con2 = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeCenterY relatedBy:0 toItem:view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];
    NSLayoutConstraint *con3 = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeWidth relatedBy:0 toItem:view attribute:NSLayoutAttributeWidth multiplier:1 constant:0];
    NSLayoutConstraint *con4 = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeHeight relatedBy:0 toItem:view attribute:NSLayoutAttributeHeight multiplier:1 constant:0];
    NSArray *constraints = @[con1,con2,con3,con4];
    [self.view addConstraints:constraints];
}

Since I use constraints fairly often, I have the above method (and others) in a categorry on UIView to keep my code looking cleaner.