Determine when UIView has finished layout

Question

I have UIView subclass, and for laying out UI elements i don't using Auto Layout. I want to set frame depends on width or height of frame. However, when i do this right after alloc]init] methods, it look like self.frame.size.height or width is zero. For temporary solution i did following:

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0.25 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
        UIImage *img = [UIImage imageNamed:@"sound_level_arrow"];
        _arrowImgView = [[UIImageView alloc] initWithFrame:CGRectMake(self.frame.size.width/2, 0, img.size.width, img.size.height)];
        _arrowImgView.center = CGPointMake(self.mainImgView.frame.size.width/2, self.mainImgView.frame.size.height-2);
        _arrowImgView.image = [UIImage imageNamed:@"sound_level_arrow"];
        _arrowImgView.contentMode   = UIViewContentModeCenter;
        [self.mainImgView addSubview:_arrowImgView];
    });

But of course i need to know, when view is finish loading and where it has actual self.frame.size.width and height.

Answer 1

If you want to do this in your custom view subclass, override layoutSubviews in that class. Since iOS may send layoutSubviews more than once, be careful to only create _arrowImgView the first time:

- (void)layoutSubviews {
    [super layoutSubviews];

    if (_arrowImgView == nil) {
        UIImage *image = [UIImage imageNamed:@"sound_level_arrow"];
        _arrowImgView = [[UIImageView alloc] initWithImage:image];
        _arrowImgView.contentMode = UIViewContentModeCenter;
        [self addSubview:_arrowImgView];
    }

    CGRect myBounds = self.bounds;
    CGRect mainFrame = self.mainImageView.frame;
    _arrowImgView.bounds = CGRectMake(0, 0, myBounds.size.width, myBounds.size.height);
    _arrowImgView.center = CGPointMake(mainFrame.size.width / 2, mainFrame.size.height - 2);
}

Answer 2

Use this one. It handles orientation changes, and redrawing of Gradient background.

import UIKit

@IBDesignable
final class GradientButton: UIButton {

    @IBInspectable var startColor: UIColor = UIColor.clear
    @IBInspectable var endColor: UIColor = UIColor.clear

    override func draw(_ rect: CGRect) {

        if let gradient = layer.sublayers?.first as? CAGradientLayer {
            gradient.removeFromSuperlayer()
        }

        let gradient: CAGradientLayer = CAGradientLayer()
        gradient.frame = CGRect(origin: CGPoint.zero, size: self.frame.size)
        gradient.colors = [startColor.cgColor, endColor.cgColor]
        layer.insertSublayer(gradient, at: 0)

        super.draw(rect)
    }

   @IBInspectable var imageContentMode: Int {
        get {
            return imageView?.contentMode.rawValue ?? 0
        }
        set {
            imageView?.contentMode = UIViewContentMode(rawValue: newValue) ?? .scaleAspectFit

        }
    }
}