is there is a way to create constraint greater than or equal relation through code

问题

I'm working on expandable table cell, and my algorithm is follow:

I create two views.
Create the height constraint of second view, drag it as IBOutlet to my cell.
When cell is selected change status of selected cell.

class ExpandableCell: UITableViewCell {

    @IBOutlet weak var expandableCellHeightConstraint: NSLayoutConstraint!

    @IBOutlet weak var expandableView: UIView!

    var isExpanded:Bool = false
    {
        didSet
        {
            if !isExpanded {
                self.expandableCellHeightConstraint.constant = 0.0

            } else {
                self.expandableCellHeightConstraint.constant = 120
            }
        }
    }
}

Everything is fine, but I want my second view resize related to inner content.

Here are my constraints:

So, my question is:

What is the best way to write non-strict value to self.expandableCellHeightConstraint.constant? Actually I thought of writing something like self.expandableCellHeightConstraint.constant >= 120, but as far as I get it is impossible.

回答1:

As Martin R suggests, you can create the height constraint in code like this:

let heightConstraint = NSLayoutConstraint(
        item: yourExpandableView,
        attribute: .height,
        relatedBy: .greaterThanOrEqual,
        toItem: nil,
        attribute: .notAnAttribute,
        multiplier: 1.0,
        constant: 120
)

Alternatively, you can do it like this:

let heightConstraint = yourExpandableView.heightAnchor.constraint(greaterThanOrEqualToConstant: 120)

Then you can set its isActive property to true or false whenever you need to enable/disable this constraint. You probably also want to hold this constraint as a property of the class, because constraints become nil, once their property isActive is set to false.

I hope it's helpful!

来源：https://stackoverflow.com/questions/44305834/is-there-is-a-way-to-create-constraint-greater-than-or-equal-relation-through-co

标签

ios

swift

autolayout

nslayoutconstraint