Fitting a UIImageView to the Image size [Swift]

Problem:

I set scaleToFit on a UIImageView and pinned its width to the screen view with constraints.

But the UIImagView's size doesn't shrink, so extra margin is left over, and I want to set up AutoLayout so the UIImageView fits the Image size.

Solution:

Store the Image's aspect ratio.
In the AutoLayout height setting, use the stored ratio to compute the height from the UIImageView's width, and set that up in AutoLayout.

private let postImageView: UIImageView = {
    let iv = UIImageView()
    iv.contentMode = .scaleAspectFit
    iv.layer.borderWidth = 1
    iv.image = #imageLiteral(resourceName: "venom-7")
    return iv
}()

addSubview(postImageView)
postImageView.snp.makeConstraints { make in
      make.top.equalTo(usernameButton.snp.bottom).offset(8)
      make.leading.equalTo(self).offset(8)
      make.trailing.equalTo(self).offset(-8)
}

This is the setup in the screenshot above.

I fixed the width by placing the leading and trailing 8 away from the view.

Now store the aspect ratio of the image in the UIImageView in a ratio variable,

let ratio: CGFloat = image.size.width / image.size.height

and then pin the height using the stored ratio against the UIImageView's current width.

postImageView.snp.makeConstraints { make in
    make.height.equalTo(self.postImageView.snp.width).multipliedBy(1/ratio)
}

Solved!!

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