How to Disable a Constraint Programmatically

Programmatically disable auto-layout constraint

When developing for iOS 8.0 or later, just use isActive property of NSLayoutConstraint after creating your IBOutlet.

UPDATED

to have strong reference to the outlet per below suggestion, thank you @rob mayoff.
to use .isActive instead of .active with Swift 4 per below suggestion, thank you @Mohit Singh.

your cell would have the following outlet:

@IBOutlet var photoBottomConstraint: NSLayoutConstraint!

and you would access the constraint in willDisplayCell like:

myCell.photoBottomConstraint.isActive = false

and when you need it again:

myCell.photoBottomConstraint.isActive = true

How to disable a constraint programmatically?

The constraints have a boolean property called active so if you want to disable a constraint you can easily call it:

constraint_A.active = false

How to deactivate my constraints?

I hope the following code will help you,

1) declare the global variables

var searchTextViewPortraitWidthConstraint: NSLayoutConstraint?
var searchTextViewLandscapeWidthConstraint: NSLayoutConstraint?
let searchTextView = UITextView()

2) viewDidLoad()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        setupSearchTextView()
        let isPortrait = UIInterfaceOrientationIsPortrait(UIApplication.shared.statusBarOrientation)
        if isPortrait {
            searchTextViewPortraitWidthConstraint = searchTextView.widthAnchor.constraint(equalToConstant: view.frame.width * 0.7)
            searchTextViewLandscapeWidthConstraint = searchTextView.widthAnchor.constraint(equalToConstant: view.frame.width * 0.1)

            searchTextViewPortraitWidthConstraint?.isActive = true
        } else {
            searchTextViewLandscapeWidthConstraint = searchTextView.widthAnchor.constraint(equalToConstant: view.frame.width * 0.1)
            searchTextViewPortraitWidthConstraint = searchTextView.widthAnchor.constraint(equalToConstant: view.frame.width * 0.7)
            searchTextViewLandscapeWidthConstraint?.isActive = true
        }
    }

configure textview

func setupSearchTextView(){
        searchTextView.frame = CGRect(x: <#T##CGFloat#>, y: <#T##CGFloat#>, width: <#T##CGFloat#>, height: <#T##CGFloat#>)
        /*
         .
         .
         .
         .
         .
         .*/
    }

3) to activate or deactivate the width constraint based on device orientation use the any one of the below approach (i.e, viewWillLayoutSubviews() or viewDidLayoutSubviews()).

override func viewWillLayoutSubviews() {
    super.viewWillLayoutSubviews()
    let isPortrait = UIInterfaceOrientationIsPortrait(UIApplication.shared.statusBarOrientation)
    if isPortrait{
        searchTextViewPortraitWidthConstraint?.isActive = true
        searchTextViewLandscapeWidthConstraint?.isActive = false
    }else{
        searchTextViewPortraitWidthConstraint?.isActive = false
        searchTextViewLandscapeWidthConstraint?.isActive = true
    }
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    let isPortrait = UIInterfaceOrientationIsPortrait(UIApplication.shared.statusBarOrientation)
    if isPortrait{
        searchTextViewPortraitWidthConstraint?.isActive = true
        searchTextViewLandscapeWidthConstraint?.isActive = false
    }else{
        searchTextViewPortraitWidthConstraint?.isActive = false
        searchTextViewLandscapeWidthConstraint?.isActive = true
    }
}

Removing/Adding constraint programmatically in ConstraintLayout

I have not worked through your code, but the following illustrates how to break and make the constraint using ConstraintSet.

ConstraintSet set = new ConstraintSet();
ConstraintLayout layout;

layout = (ConstraintLayout) findViewById(R.id.layout);
set.clone(layout);
// The following breaks the connection.
set.clear(R.id.bottomText, ConstraintSet.TOP);
// Comment out line above and uncomment line below to make the connection.
// set.connect(R.id.bottomText, ConstraintSet.TOP, R.id.imageView, ConstraintSet.BOTTOM, 0);
set.applyTo(layout);

How to properly enable and disable constraint in one view controller on button click

Problem is each time you click the button 1 of the cases fire which eventualy call setupInputFields and cause re-addition of new constraints which may conflict with old ones , so either access old constraints and delete them or create 2 arrays of possible variations and play with activate/deactivate

Removing constraints that were added programatically

You should assign your constraint to a property in your ViewController. And then set .isActive to false instead of true.

Your code should look like this:

let myConstraint = firstView.topAnchor.constraint(equalTo: secondView.bottomAnchor, constant: 15)

Now, to activate it:

myConstraint.isActive = true

And to disable it:

myConstraint.isActive = false

How to remove constraints programmatically that is added from storyboard?

As @Henit mentioned, you can set IBOutlet for constraints as well.

For example,

@property(weak, nonatomic) IBOutlet NSLayoutConstraint *viewHeight;

so now, you can remove this constraint like this:

[myView removeConstraint: viewHeight];

Or else if you want to remove all / multiple constraints related to your view then,

[myView removeConstraints: constraintsArrayHere]; // custom array of constraints references
[myView removeConstraints: [myView constraints]]; //all constraints

Then later you can add your new constraints in the same manner using addConstraint or addConstraints method.

For more details go through Apple Documentation here.

Hope this helps.