NSLayoutConstraint between Navigation Bar & ViewControllers View

Add the constraint between the top of the textField and the top of the parent view. The constant for the constraint can be set to the height of the status bar + height of the navigation bar.

Obviously, the following code snippet will only work if both the Status Bar and Navigation Bar are translucent and the view controller wants full screen layout. You can easily test for transparency and adjust accordingly, if necessary.

If you're using interface builder, you can also create an IBOutlet for the existing constraint and just set it's constant rather than creating a new constraint.

// Obtain the view rect of the status bar frame in either portrait or landscape
CGRect statusBarFrame = [[UIApplication sharedApplication] statusBarFrame];
CGRect statusBarWindowRect = [self.view.window convertRect:statusBarFrame fromWindow: nil];
CGRect statusBarViewRect = [self.view convertRect:statusBarWindowRect fromView: nil];

// Add Status Bar and Navigation Bar heights together
CGFloat height = self.navigationController.navigationBar.frame.size.height +
statusBarViewRect.size.height;

// Create & Add Constraint
NSLayoutConstraint *constraint =
[NSLayoutConstraint constraintWithItem:self.fieldLabel
                             attribute:NSLayoutAttributeTop
                             relatedBy:0
                                toItem:self.view
                             attribute:NSLayoutAttributeTop
                            multiplier:1
                              constant:height];

[self.view addConstraint:constraint];

Yes you can add a constraint between the Navigation Bar and a view. Your root view conroller added to the navigation controller contains topLayoutGuide. so adjust your code like this:

NSLayoutConstraint* cn = [NSLayoutConstraint constraintWithItem:_textField
                                                      attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual
                                                         toItem:self.rootViewController.topLayoutGuide attribute:NSLayoutAttributeBottom
                                                     multiplier:1.0 constant:20];
[self.rootViewController.view addConstraint:cn];

notice that i'm not referencing the navigation controller at all but the rootViewController of the navigation Controller.

Also you can use bottomLayoutGuide to go above the TabBar the same way. (however if you need to do that you'll run into a bug in iOS frameworks with a workaround patch here: UIViews ending up beneath tab bar )