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

While this may not be quite what you're after - the background image does scale.

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Try this:

[button setImage:image forState:UIControlStateNormal];
button.contentVerticalAlignment = UIControlContentVerticalAlignmentFill;
button.contentHorizontalAlignment = UIControlContentHorizontalAlignmentFill;

In Swift:

button.contentVerticalAlignment = .fill
button.contentHorizontalAlignment = .fill

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Remember to set Control Alignment settings for the button

https://i.stack.imgur.com/t4615.png

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I know this is old, but I think that the correct answer is that you should set the content mode to the "hidden" UIImageView that is inside the UIButton:

button.imageView.contentMode = UIViewContentModeScaleAspectFill;

This will change the content mode for the images views of the images set with:

[button setImage:yourAwesomeImage forState:UIControlStateNormal]; 
//Or any other state

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Just do (From Design OR From Code):

From Design

Open your xib OR Storyboard. Select button Inside Attribute Inspector (Right side) > In "Control" section > select last 4th option for both Horizontal and Verical.

[For Point#3: Change Horizontal and vertical Align to UIControlContentHorizontalAlignmentFill and UIControlContentVericalAlignmentFill]

From Code

button.contentHorizontalAlignment = UIControlContentHorizontalAlignmentFill; button.contentVerticalAlignment = UIControlContentVerticalAlignmentFill;

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Inside Attribute Inspector first set Type "Custom" and Style "Default" then Set alignment Horizontal and Vertical both "fill".

https://i.stack.imgur.com/pvqUn.png

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Interface Builder

To get images in UIButtons to scale the same way as UIViews in interface Builder follow these steps:

Select your UIButton and from the Identity Inspector add the following to User Defined Runtime Attributes:

imageView.contentMode Number 1

Where number is the enum number of contentMode, eg:

0 = Scale to fill 
1 = Aspect Fit 
2 = Aspect Fill
etc..

Then open the Attributes editor for your UIButton and under Control set the Alignment to Fill (last button on right) for both horizontal and vertical.

SWIFT 3

Note you can also do this in code with the following:

button.imageView?.contentMode = .scaleAspectFit
button.contentVerticalAlignment = .fill
button.contentHorizontalAlignment = .fill

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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

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Try setting the Clip subviews property in Interface Builder to true.

Hope that helps.

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The best solution I found so far in Swift 2.1 is the following:

self.imageButton.imageView?.clipsToBounds = true
self.imageButton.imageView?.contentMode = UIViewContentMode.ScaleAspectFit

This will scale the image so it has an aspect fit in the imageView.

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Just get a real UIimageview and place a UIbutton on top of it and via layout menu set it to back. Then you can scale your image properly.

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