I was trying to update the height constraint of my view during an animation. Its not getting updated why..?

Here is how i have configured the profile view,

-(void)addProfileView
{
    if(!_profileView)
    {
        _profileView = [ProfileView new];
        _profileView.clipsToBounds = YES;
        _profileView.delegate=self;
        _profileView.alpha = 1.0;
        _profileView.opaque = YES;
        _profileView.translatesAutoresizingMaskIntoConstraints = false;
        [self.view addSubview:_profileView];
        NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:_profileView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0 constant:160];
        NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:_profileView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:1 constant:0];
        NSLayoutConstraint *leftConstraint = [NSLayoutConstraint constraintWithItem:_profileView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1 constant:0];
        NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:_profileView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1 constant:-64];
        [NSLayoutConstraint activateConstraints:@[heightConstraint, widthConstraint, leftConstraint, topConstraint]];
    }
}

Now, why is the profile view's height not changing after the animation? Should I add the constraints to the superview? What's the difference between adding constraints directly to the superview and using [NSLayoutConstraint activateConstraints:@[]] ?

-(void)animateProfileViewBasedOnOffset:(BOOL)isTop
{
__block NSLayoutConstraint *heightConstraint;
    
    for (NSLayoutConstraint * constraint in [_profileView constraints]) {
        if (constraint.firstAnchor == NSLayoutAttributeHeight) {
            heightConstraint = constraint;
            break;
        }
    }
    
    [UIView animateWithDuration:0.3 animations:^{
        if (isTop) {
            heightConstraint.constant = 64;
        }
        else {
            heightConstraint.constant = 160;
        }
        [_profileView layoutIfNeeded];
        [self.view layoutIfNeeded];
    }completion:^(BOOL completion)
     {
         NULL;
     }];
}

The height of the profileView only changes when I add its constraint to the superview ([self.view addConstraints:@[]]). During the animation, I loop through all the constraints of the superview to find the specific constraint and update it.

You should check and confirm that you are, in fact, finding the Height constraint:

for (NSLayoutConstraint * constraint in [_profileView constraints]) {
    if (constraint.firstAnchor == NSLayoutAttributeHeight) {
        heightConstraint = constraint;
        break;
    }
}
if (heightConstraint) {
    NSLog(@"Found Height Constraint: %@", heightConstraint);
} else {
    NSLog(@"Did NOT find Height Constraint!");
}

That code (in my quick test) does NOT find the Height constraint, so of course, no animation.

This code:

for (NSLayoutConstraint *constraint in _profileView.constraints) {
    // Check if the constraint is a height constraint
    if (constraint.firstAttribute == NSLayoutAttributeHeight && constraint.firstItem == _profileView) {
        // Found the height constraint
        heightConstraint = constraint;
        break;
    }
}
if (heightConstraint) {
    NSLog(@"Found Height Constraint: %@", heightConstraint);
} else {
    NSLog(@"Did NOT find Height Constraint!");
}

Does find the Height constraint, and the animation happens as expected.

As a side note, you might want to look at the more modern way of setting up constraints. This matches your constraints, but I think you'd agree it is much more readable (and much easier to edit when needed):

[NSLayoutConstraint activateConstraints:@[
    [_profileView.heightAnchor constraintEqualToConstant:160.0],
    [_profileView.widthAnchor constraintEqualToAnchor:self.view.widthAnchor],
    [_profileView.leftAnchor constraintEqualToAnchor:self.view.leftAnchor],
    [_profileView.topAnchor constraintEqualToAnchor:self.view.topAnchor constant:-64.0],
]];

Edit

As mentioned in comments by Matt, you are (almost always) better off adding a constraint property that you can update when desired.

Here's an example of that approach:

#import <UIKit/UIKit.h>

@interface AnimSubViewController : UIViewController
@end

@interface AnimSubViewController ()
@property (strong, nonatomic) UIView *profileView;
@property (strong, nonatomic) NSLayoutConstraint *heightConstraint;
@end

@implementation AnimSubViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = UIColor.systemBackgroundColor;
    
    [self addProfileView];
}

-(void)addProfileView
{
    if(!_profileView)
    {
        //_profileView = [ProfileView new];
        _profileView = [UIView new];
        _profileView.backgroundColor = UIColor.redColor;
        _profileView.clipsToBounds = YES;
        //_profileView.delegate=self;
        _profileView.alpha = 1.0;
        _profileView.opaque = YES;
        _profileView.translatesAutoresizingMaskIntoConstraints = false;
        [self.view addSubview:_profileView];

        // set the _heightConstraint property, so we can modify its .constant later
        _heightConstraint = [_profileView.heightAnchor constraintEqualToConstant:160.0];
        
        [NSLayoutConstraint activateConstraints:@[
            //[_profileView.heightAnchor constraintEqualToConstant:160.0],
            _heightConstraint,
            [_profileView.widthAnchor constraintEqualToAnchor:self.view.widthAnchor],
            [_profileView.leftAnchor constraintEqualToAnchor:self.view.leftAnchor],
            [_profileView.topAnchor constraintEqualToAnchor:self.view.topAnchor constant:-64.0],
        ]];

    }
}

-(void)animateProfileViewBasedOnOffset:(BOOL)isTop
{

    [UIView animateWithDuration:0.3 animations:^{
        if (isTop) {
            self->_heightConstraint.constant = 64;
        }
        else {
            self->_heightConstraint.constant = 160;
        }
        // not needed
        //[self->_profileView layoutIfNeeded];
        
        [self.view layoutIfNeeded];
        
    } completion:^(BOOL completion) {
        NULL;
    }];
    
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    // hide/show _profileView on tap anywhere
    [self animateProfileViewBasedOnOffset:_heightConstraint.constant == 160.0];
}

@end