• Swift

import Foundation
import UIKit

enum UIButtonImageTitlePositionType {
    case imageLeftTitleRight
    case imageRightTitleLeft
    case imageUpTitleDown
    case imageDownTitleUp
}

extension UIButton {
    func adjustsImageTitlePosition(type: UIButtonImageTitlePositionType = .imageUpTitleDown, spacing: CGFloat = 6.0) {
        switch type {
        case .imageUpTitleDown:
            guard let imageSize = self.imageView?.image?.size,
                let text = self.titleLabel?.text,
                let font = self.titleLabel?.font else {
                    return
            }
            
            self.titleEdgeInsets = UIEdgeInsets(top: 0.0, left: -imageSize.width, bottom: -(imageSize.height + spacing), right: 0.0)
            
            let labelString = NSString(string: text)
            let titleSize = labelString.size(withAttributes: [NSAttributedString.Key.font: font])
            self.imageEdgeInsets = UIEdgeInsets(top: -(titleSize.height + spacing), left: 0.0, bottom: 0.0, right: -titleSize.width)
            
            let edgeOffset = abs(titleSize.height - imageSize.height) / 2.0;
            self.contentEdgeInsets = UIEdgeInsets(top: edgeOffset, left: 0.0, bottom: edgeOffset, right: 0.0)
        default:
            break
        }
    }
}

• Objective-C

/ the space between the image and text
CGFloat spacing = 6.0;

// lower the text and push it left so it appears centered 
//  below the image
CGSize imageSize = button.imageView.image.size;
button.titleEdgeInsets = UIEdgeInsetsMake(
  0.0, - imageSize.width, - (imageSize.height + spacing), 0.0);

// raise the image and push it right so it appears centered
//  above the text
CGSize titleSize = [button.titleLabel.text sizeWithAttributes:@{NSFontAttributeName: button.titleLabel.font}];
button.imageEdgeInsets = UIEdgeInsetsMake(
  - (titleSize.height + spacing), 0.0, 0.0, - titleSize.width);

// increase the content height to avoid clipping
CGFloat edgeOffset = fabsf(titleSize.height - imageSize.height) / 2.0;
button.contentEdgeInsets = UIEdgeInsetsMake(edgeOffset, 0.0, edgeOffset, 0.0);

參考：

• https://stackoverflow.com/questions/2451223/uibutton-how-to-center-an-image-and-a-text-using-imageedgeinsets-and-titleedgei/7199529#7199529