Nested @IBDesignables using xibs?

Question

I'm trying to create a component-based system on iOS, and I'd like to do the following:

1. Create a "PaddedView" component that has 8px of space around any added child components, like a container type component.

2. Add another IBDesignable view into this PaddedView on a storyboard, and see both render.

Is this possible?

Right now, I'm using the following superclass for all IBDesignable components to load their views from xibs:

import Foundation
import UIKit

@IBDesignable
class SKDesignableView: UIView {
    var view: UIView?

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.loadXib()
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.loadXib()
    }

    func loadXib() {
        self.view = self.viewFromXib()
        self.view!.frame = self.bounds
        self.view!.autoresizingMask = [UIViewAutoresizing.flexibleWidth, UIViewAutoresizing.flexibleHeight]
        self.addSubview(self.view!)
    }

    func viewFromXib() -> UIView {
        let bundle = UINib(nibName: String(describing: self.getType()), bundle: Bundle(for: self.getType()))
        let views = bundle.instantiate(withOwner: self, options: nil)
        return views.first as! UIView
    }

    func getType() -> AnyClass {
        fatalError()
    }
}

How do I create placeholders for other IBDesignables?

Answer 1

The view initially contains the children, so add a container view as a subview to any component that needs children.

func loadXib() {
        var subview: UIView? = nil
        if self.subviews.count > 0 {
            subview = self.subviews[0]
        }
        subview?.removeFromSuperview()

        self.view = self.viewFromXib()
        self.view!.frame = self.bounds
        self.view!.autoresizingMask = [UIViewAutoresizing.flexibleWidth, UIViewAutoresizing.flexibleHeight]

        if let subview = subview {
            let lConstraint = NSLayoutConstraint(item: subview, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal,
                    toItem: self.view!, attribute: NSLayoutAttribute.leading, multiplier: 1, constant: 8)
            let rConstraint = NSLayoutConstraint(item: subview, attribute: NSLayoutAttribute.trailing, relatedBy: NSLayoutRelation.equal,
                    toItem: self.view!, attribute: NSLayoutAttribute.trailing, multiplier: 1, constant: -8)
            let tConstraint = NSLayoutConstraint(item: subview, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal,
                    toItem: self.view!, attribute: NSLayoutAttribute.top, multiplier: 1, constant: 8)
            let bConstraint = NSLayoutConstraint(item: subview, attribute: NSLayoutAttribute.bottom, relatedBy: NSLayoutRelation.equal,
                    toItem: self.view!, attribute: NSLayoutAttribute.bottom, multiplier: 1, constant: -8)
            self.view!.addSubview(subview)
            self.view!.addConstraints([lConstraint, rConstraint, tConstraint, bConstraint])
        }
        self.addSubview(self.view!)
    }

This approach can be generalized with tags etc to add multiple subviews.