ios add button autolayout - ios

Question

I insert a button to a view in storyboard like following:
and I need to add a custom constrain to the bottom using following code:
- (void)viewDidLoad
{
[super viewDidLoad];
NSDictionary *viewsDictionary = [NSDictionary dictionaryWithObject:self.bottomButton forKey:#"bottomButton"];
NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:#"[bottomButton]-90-|" options:0 metrics:nil views:viewsDictionary];
NSArray *v_constraints = [NSLayoutConstraint constraintsWithVisualFormat:#"V:[bottomButton]-20-|" options:0 metrics:nil views:viewsDictionary];
[self.bottomButton.superview addConstraints:constraints];
[self.bottomButton.superview addConstraints:v_constraints];
}
but there's a conflict, the error is
Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSIBPrototypingLayoutConstraint:0x8c57fb0 'IB auto generated at build time for view with fixed frame' H:|-(254)-[UIButton:0x8c56440](LTR) (Names: '|':UIView:0x8c56af0 )>",
"<NSIBPrototypingLayoutConstraint:0x8c58de0 'IB auto generated at build time for view with fixed frame' H:[UIButton:0x8c56440(46)]>",
"<NSLayoutConstraint:0x8c4fc30 H:[UIButton:0x8c56440]-(90)-| (Names: '|':UIView:0x8c56af0 )>",
"<NSAutoresizingMaskLayoutConstraint:0x8c62320 h=--& v=--& H:[UIView:0x8c56af0(320)]>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x8c4fc30 H:[UIButton:0x8c56440]-(90)-| (Names: '|':UIView:0x8c56af0 )>
Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSIBPrototypingLayoutConstraint:0x8c58d30 'IB auto generated at build time for view with fixed frame' V:|-(361)-[UIButton:0x8c56440] (Names: '|':UIView:0x8c56af0 )>",
"<NSIBPrototypingLayoutConstraint:0x8c58e10 'IB auto generated at build time for view with fixed frame' V:[UIButton:0x8c56440(30)]>",
"<NSLayoutConstraint:0x8c527c0 V:[UIButton:0x8c56440]-(20)-| (Names: '|':UIView:0x8c56af0 )>",
"<NSAutoresizingMaskLayoutConstraint:0x8c62380 h=--& v=--& V:[UIView:0x8c56af0(568)]>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x8c527c0 V:[UIButton:0x8c56440]-(20)-| (Names: '|':UIView:0x8c56af0 )>
Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
how to fix it?

Answer 1

It's happening because even though you haven't set constraints explicitly in IB they're automatically added on runtime, e.g.
"<NSIBPrototypingLayoutConstraint:0x8c57fb0 'IB auto generated at build time for view with fixed frame' H:|-(254)-[UIButton:0x8c56440](LTR) (Names: '|':UIView:0x8c56af0 )>",
Please watch the session 406 from WWDC 2013. The current best practice is to set your constraints in IB, and then only modify/add constraints in code which can't be set using IB.