如何删除以编程方式添加的约束

Question

How to remove this constraint programmatically. please help

cell.textView.addConstraint(NSLayoutConstraint(item: cell.textView, attribute: .height, relatedBy: .greaterThanOrEqual,
                                                           toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 54))

that code is added in tablecells .i want to remove when keyboard hide.

Answer 1

So it seems you want to remove just this one constraint, without interfering with default ones. The simplest way would be, of course, to just keep a reference to this constraint and to disable it.

let constraint = NSLayoutConstraint(item: cell.textView, 
                               attribute: .height, 
                               relatedBy: .greaterThanOrEqual, 
                                  toItem: nil, 
                               attribute: .notAnAttribute,
                              multiplier: 1.0, constant: 54)
cell.textView.addConstraint(constraint)
strongReferenceToConstraint = constraint

/// somewhere else 

cell.textView.removeConstraint(strongReferenceToConstraint)

But if you can't keep reference to it, or for some reason it's not accessible to you, you can try iterating over all constraints of this view and finding the one on height by checking its firstAttribute property

for constraint in cell.textView.constraints
{
    if constraint.firstAttribute == .height
    {
        constraint.isActive = false
        break
    }
}

Answer 2

var constraint = NSLayoutConstraint(item: cell.textView, attribute: .height, relatedBy: .greaterThanOrEqual,
                                                           toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 54)

constraint.isActive = false