AutoLayout

[NSLayoutConstraint constraintsWithVisualFormat:@"V:[superview]-(<=1)-[subview]"] options:NSLayoutFormatAlignAllCenterX metrics:nil views:views]; NSLayoutConstraint *c2 = constraintWithItem:firstView attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:secondView attribute:NSLayoutAttributeLeading multiplier:1 constant:0];

2015-08-26 14:27:54.790 Auto Layout Cookbook[10040:1906606] 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) ( "<NSLayoutConstraint:0x7a87b000 H:[UILabel:0x7a8724b0'Name'(>=400)]>", "<NSLayoutConstraint:0x7a895e30 UILabel:0x7a8724b0'Name'.leading == UIView:0x7a887ee0.leadingMargin>", "<NSLayoutConstraint:0x7a886d20 H:[UILabel:0x7a8724b0'Name']-(NSSpace(8))-[UITextField:0x7a88cff0]>", "<NSLayoutConstraint:0x7a87b2e0 UITextField:0x7a88cff0.trailing == UIView:0x7a887ee0.trailingMargin>", "<NSLayoutConstraint:0x7ac7c430 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7a887ee0(320)]>" ) Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7a87b000 H:[UILabel:0x7a8724b0'Name'(>=400)]> Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger. The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

<NSAutoresizingMaskLayoutConstraint:0x7ff28252e480 h=--& v=--& H:[UIView:0x7ff282617cc0(50)]>"

// Don’t do this! Removes and re-adds constraints potentially at 120 frames per second override func updateConstraints() { NSLayoutConstraint.deactivate(myConstraints) myConstraints.removeAll() let views = ["text1":text1, "text2":text2] myConstraints+=NSLayoutConstraint.constraints(withVisualFormat: "H:|-[text1]-[text2]", options: [.alignAllFirstBaseline], metrics: nil, views: views) myConstraints+=NSLayoutConstraint.constraints(withVisualFormat: "V:|-[text1]-|", options: [], metrics: nil, views: views) NSLayoutConstraint.activate(myConstraints) super.updateConstraints() }

// Don’t do this! Removes and re-adds constraints potentially at 120 frames per second override func layoutSubviews() { text1.removeFromSuperview() text1 = nil text1 = UILabel(frame: CGRect(x: 20, y: 20, width: 300, height: 30)) self.addSubview(text1) text2.removeFromSuperview() text2 = nil text2 = UILabel(frame: CGRect(x: 340, y: 20, width: 300, height: 30)) self.addSubview(text2) super.layoutSubviews() }

// This is ok! Doesn’t do anything unless self.myConstraints has been nil’d out override func updateConstraints() { if self.myConstraints == nil { var constraints = [NSLayoutConstraint]() let views = ["text1":text1, "text2":text2] constraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|-[text1]-[text2]",options: [.alignAllFirstBaseline], metrics: nil, views: views) constraints += NSLayoutConstraint.constraints(withVisualFormat: "V:|-[text1]-|", options: [], metrics: nil, views: views)} NSLayoutConstraint.activate(constraints) self.myConstraints = constraints } super.updateConstraints() }

- (void)layoutSubviews { [super layoutSubviews]; myLabel.preferredMaxLayoutWidth = myLabel.frame.size.width; [super layoutSubviews]; } @implementation MyLabel - (void)layoutSubviews { self.preferredMaxLayoutWidth = self.frame.size.width; [super layoutSubviews]; }

(void)layoutSubviews { [super layoutSubviews]; myLabel.preferredMaxLayoutWidth = myLabel.frame.size.width; [super layoutSubviews]; }

[UIView animateWithDuration:1 animations:^{ myView.frame = newFrame; }]; // update constraints [UIView animateWithDuration:1 animations:^{ [myView layoutIfNeeded]; }]; [UIView animateWithDuration:1 animations:^{ myView.transform = CGAffineTransformMakeScale(.5, .5); }];