以编程方式更改约束仅影响视图的可见部分

Question

I built a TableView with static cells in Interface Builder with two sets of constraints. One for an editing view and one just for viewing. It is not much just changing the position of three textboxes.

The first set of constraints is activated in the interface builder and the second one is deactivated ("Installed" is not checked).

Then when the user clicks on "Edit" at first the old constraints are deactivated and the other ones are activated:

@IBOutlet var nonEditableConstraints: [NSLayoutConstraint]!
@IBOutlet var editableConstraints: [NSLayoutConstraint]!

override func setEditing(editing: Bool, animated: Bool) {
        super.setEditing(editing, animated: animated)

        view.layoutIfNeeded()

        if (animated) {
            UIView.animateWithDuration(1.0) { () -> Void in
                self.setControlsEditing(editing)
                self.setContraintsEditing(editing)
                self.view.layoutIfNeeded()
            }
        } else {
            setControlsEditing(editing)
            setContraintsEditing(editing)
        }
    }

private func setContraintsEditing(editing: Bool) {
        // we need to make sure to deakcivate constraints before activating new ones
        if (editing) {
            for constraint in nonEditableConstraints {
                constraint.active = false
            }

            for constraint in editableConstraints {
                constraint.active = true
            }
        } else {
            for constraint in editableConstraints {
                constraint.active = false
            }

            for constraint in nonEditableConstraints {
                constraint.active = true
            }
        }
    }

This works well. The only thing is that whenever a part of the three "macro nutrition" fields which are subject to constraint changes are not visible when the constraints are changed they stay in their default state (the state set by IB). This occurs when the iPhone is in landscape mode. A few examples:

This is how it looks in default mode (set by IB):

When I press Edit while all three textboxes are visible (correctly layoutet):

This is how it looks in landscape when I pressed edit before scrolling down (carbohydrates were not visible). When I press Done and that Edit again everything is correct since all textboxes are visible:

Answer 1

I solved it myself. Apparently you should only change constraints in the viewDidLayoutSubviews() method of the view controller. I changed the code in this way which is working:

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    setContraintsEditing(editing)
}

override func setEditing(editing: Bool, animated: Bool) {
    super.setEditing(editing, animated: animated)

    if (animated) {
        view.layoutIfNeeded()
        UIView.animateWithDuration(1.0) { () -> Void in
            self.setControlsEditing(editing)
            self.view.layoutIfNeeded()
        }
    } else {
        setControlsEditing(editing)
    }
}

As you see the setContraintsEditing(bool) method now is called from the right place which is called by the animation block indirectly by layoutIfNeeded().