Add UIView to UIScrollView after UIScrollView init

[zkhCreator]

I use the demo about UIScrollView,and I want to append a UIView a UIView after the UIScrollView init,like: I click a button,than there is a new UIView at the bottom of the UIScrollView. So I write the code like this:

- (void)clickButton{
    UIView *new = [[UIView alloc]init];
    new.backgroundColor = [UIColor blueColor];

    [self.scrollView.contentView addSubview:new];
    [new mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(self.scrollView.lastBottom);
        make.left.equalTo(@0);
        make.right.equalTo(self.scrollView.contentView.mas_right);
        make.height.equalTo(@50);
    }];

    self.scrollView.lastBottom = new.mas_bottom;

    [self.scrollView.contentView mas_updateConstraints:^(MASConstraintMaker *make) {
        make.bottom.equalTo(self.scrollView.lastBottom);
    }];
}

But there still an error like

(
    "<MASLayoutConstraint:0x7f97f431b360 UIView:content.bottom == UIView:newView.bottom>",
    "<MASLayoutConstraint:0x7f97f4341400 UIView:newView.top == UIView:newView.bottom>",
    "<MASLayoutConstraint:0x7f97f4341bb0 UIView:newView.height == 50>",
    "<MASLayoutConstraint:0x7f97f4315390 UIView:content.bottom == UIView:newView.bottom>"
)

Will attempt to recover by breaking constraint 
<MASLayoutConstraint:0x7f97f4341bb0 UIView:newView.height == 50>

It means I didnot update my constraint after update.How to solve the problem?

[robertjpayne]

@zkh90644 mas_updateConstraints only updates matching constraints in this case you did not previously have a bottom.equalTo(self.scrollView.lastBottom) so it's actually creating a new constraint and you have two constraints.

You'll need to use mas_remakeConstraints and recreate all of them to get this behavior.