Updating Constraint contant?

[nickvelloff]

If I hang onto a constraint like:

var leftConstraint: Constraint?
let padding = UIEdgeInsetsMake(107, 0, 0, 0)
     draftsSiteManagement?.snp_makeConstraints { make in
            make.size.equalTo(self.view).with.insets(padding)
            make.top.equalTo(107)
            self.leftConstraint = make.left.equalTo(self.view.snp_right)
        }
}

How would I update the constant later?

[robertjpayne]

Define how you would like to update said constraint? Are you looking to just update the "constant" or also re-assign the LHS/RHS?

If you strictly say want to update that 107 to maybe 40 or something you would just need to:

snp_updateConstraints { make in
    make.top.equalTo(40)
}

[nickvelloff]

Thanks for responding.
I would like to update the self.leftConstraint constant such that left is now = self.view.snp_left, instead of right.
The real goal is to animate draftsSiteManagement from where is off screen to 0 (on screen).
Basically like I would do with a standard NSLayoutConstraint constraint.constant = 5

[nickvelloff]

After reading your other response to my other question I think I'm not approaching this properly.
I probably need to uninstall the constraint and apply a new one and layoutIfNeeded() in an animation block.

[robertjpayne]

@nickvelloff it's important to note there are a couple parts to a constraint. Remember the constant is strictly the offset value of the constraint. Constraints are formulated as such:

(LHS) (RELATION) (RHS)? * (MULTIPLIER) + (CONSTANT)

The RHS can be nil, in cases where you do an equalTo(<non-view-value>) you are actually essentially doing: equalTo(nil).offset(<non-view-value>).

So yes in your particular case you are altering the LHS/RHS of the constraint and thus need a new one.

[nickvelloff]

I was confusing the meaning of self.view.snp_right with it evaluating that value and using it as a <non-view-value> constant. Newbie mistake, thanks for the clarification.