whichone?

option 1:
NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:myScrollView
                                                                       attribute:NSLayoutAttributeWidth
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:self.view
                                                                       attribute:NSLayoutAttributeWidth
                                                                      multiplier:1.0
                                                                        constant:0];

option 2:
NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:self.view
                                                                       attribute:NSLayoutAttributeWidth
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:myScrollView
                                                                       attribute:NSLayoutAttributeWidth
                                                                      multiplier:1.0
                                                                        constant:0];