Cannot change the height of Login Button in FBSDKLoginKit?

As for now the Facebook button has only one constraint which is the height constraint and you can just remove all constraints of the button and add yours.

facebookSignInButton.removeConstraints(facebookSignInButton.constraints)

But of course this can change in the future and you might remove a constraint that you don't want to. Maybe a better solution would be if you remove only that problematic constraint.

if let facebookButtonHeightConstraint = facebookSignInButton.constraints.first(where: { $0.firstAttribute == .height }) {
    facebookSignInButton.removeConstraint(facebookButtonHeightConstraint)
}

You can conveniently achieve this with a simple override of the facebook button.

Swift:

class FacebookButton: FBSDKLoginButton {

    override func updateConstraints() {
        // deactivate height constraints added by the facebook sdk (we'll force our own instrinsic height)
        for contraint in constraints {
            if contraint.firstAttribute == .height, contraint.constant < standardButtonHeight {
                // deactivate this constraint
                contraint.isActive = false
            }
        }
        super.updateConstraints()
    }

    override var intrinsicContentSize: CGSize {
        return CGSize(width: UIViewNoIntrinsicMetric, height: standardButtonHeight)
    }

    override func imageRect(forContentRect contentRect: CGRect) -> CGRect {
        let logoSize: CGFloat = 24.0
        let centerY = contentRect.midY
        let y: CGFloat = centerY - (logoSize / 2.0)
        return CGRect(x: y, y: y, width: logoSize, height: logoSize)
    }

    override func titleRect(forContentRect contentRect: CGRect) -> CGRect {
        if isHidden || bounds.isEmpty {
            return .zero
        }

        let imageRect = self.imageRect(forContentRect: contentRect)
        let titleX = imageRect.maxX
        let titleRect = CGRect(x: titleX, y: 0, width: contentRect.width - titleX - titleX, height: contentRect.height)
        return titleRect
    }

}

In this code sample standardButtonHeight is a defined constant with the desired button height.

Also note that the logo size of 24.0 is the same size used in version 4.18 of the SDK.

I've also run into this problem. The reason for this is explained in the 4.18.0 to 4.19.0 upgrade guide:

The FBSDKLoginButton UI has changed in 4.19.0. Instead of "Log in with Facebook", the button now displays "Continue with Facebook". The button color is changed to #4267B2 from #3B5998. The button height is now fixed at 28 due to use of smaller font size and paddings around a larger Facebook logo.

The only workaround I found so far is to downgrade the SDK version to 4.18.0 (it did the job for me).

It is possible that FB will address this issue (...that they've created for many people) in one of the future updates to the SDK.

---

Towards a more permanent solution, we can see the specific changes that caused this, on GitHub. The change I find most suspicious starts on line 194:

[self addConstraint:[NSLayoutConstraint constraintWithItem:self
                                                 attribute:NSLayoutAttributeHeight
                                                 relatedBy:NSLayoutRelationEqual
                                                    toItem:nil
                                                 attribute:NSLayoutAttributeNotAnAttribute
                                                multiplier:1
                                                  constant:28]];

If the above constraint is removed/disabled, it could help reverse the situation. It should look approximately like this (I don't have an IDE at hand at the time of writing):

// Obtain all constraints for the button:
let layoutConstraintsArr = fbLoginButton.constraints
// Iterate over array and test constraints until we find the correct one:
for lc in layoutConstraintsArr { // or attribute is NSLayoutAttributeHeight etc.
   if ( lc.constant == 28 ){
     // Then disable it...
     lc.active = false
     break
   }
}

When I get a chance to test the above or if I find a better solution, I'll update the answer.