Why does a custom UIButton image does not resize in Interface Builder?

Question

Why does a custom UIButton image not resize with the button?

I set its view mode to Scale to Fill in Interface Builder, but unlike a UIImageView image, it d

Answer 1

Updating this post will full answer for Swift 5:

//Set button's image
let image = UIImage(systemName: "heart.fill") //Your image here
button.setImage(image, for: .normal)

//Optional: Remove background image if you added one on accident
button.setBackgroundImage(nil, for: .normal)

//Optional: Set button's title (displayed next to button's image)
button.setTitle(nil, for: .normal)

//The button's "content" includes the title label and image
//So we set the button's content to fill the button
//If title label is nil, the content will only show the image
button.contentVerticalAlignment = .fill
button.contentHorizontalAlignment = .fill

//Set button's image to desired content mode (aspectFit avoids distortion)
//This restricts the image from resizing to fill the entire content area
button.imageView?.contentMode = .scaleAspectFit