constraints p2

    NSLayoutConstraint *rightConstraint = [NSLayoutConstraint constraintWithItem:self.mainView
                                                                       attribute:NSLayoutAttributeLeft
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:scrollViewForAccordian
                                                                       attribute:NSLayoutAttributeLeft
                                                                      multiplier:1.0
                                                                        constant:0];

    NSLayoutConstraint *bottomConstraint = [NSLayoutConstraint constraintWithItem:self.mainView
                                                                       attribute:NSLayoutAttributeBottom
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:scrollViewForAccordian
                                                                       attribute:NSLayoutAttributeBottom
                                                                      multiplier:1.0
                                                                        constant:0];

    NSLayoutConstraint *leftConstraint = [NSLayoutConstraint constraintWithItem:self.mainView
                                                                       attribute:NSLayoutAttributeRight
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:scrollViewForAccordian
                                                                       attribute:NSLayoutAttributeRight
                                                                      multiplier:1.0
                                                                        constant:0];

    NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:self.mainView
                                                                       attribute:NSLayoutAttributeTop
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:scrollViewForAccordian
                                                                       attribute:NSLayoutAttributeTop
                                                                      multiplier:1.0
                                                                        constant:0];

    scrollViewForAccordian.translatesAutoresizingMaskIntoConstraints = NO;

    [mainView addConstraints:@[leftConstraint, bottomConstraint, topConstraint, rightConstraint]];

    scrollViewForAccordian.backgroundColor = [UIColor redColor];