Slow load time for custom UIView in Swift

Question

Background

In order to make a text view that scrolls horizontally for vertical Mongolian script, I made a custom UIView subclass. The class takes a UITextView, puts it in a UIView, rotates and flips that view, and then puts that view in a parent UIView.

The purpose for the rotation and flipping is so that the text will be vertical and so that line wrapping will work right. The purpose of sticking everything in a parent UIView is so that Auto layout will work in a storyboard. (See more details here.)

Code

I got a working solution. The full code on github is here, but I created a new project and stripped out all the unnecessary code that I could in order to isolate the problem. The following code still performs the basic function described above but also still has the slow loading problem described below.

import UIKit

@IBDesignable class UIMongolTextView: UIView {

    private var view = UITextView()
    private var oldWidth: CGFloat = 0
    private var oldHeight: CGFloat = 0

    @IBInspectable var text: String {
        get {
            return view.text
        }
        set {
            view.text = newValue
        }
    }

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

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

    override func sizeThatFits(size: CGSize) -> CGSize {
        // swap the length and width coming in and going out
        let fitSize = view.sizeThatFits(CGSize(width: size.height, height: size.width))
        return CGSize(width: fitSize.height, height: fitSize.width)
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        // layoutSubviews gets called multiple times, only need it once
        if self.frame.height == oldHeight && self.frame.width == oldWidth {
            return
        } else {
            oldWidth = self.frame.width
            oldHeight = self.frame.height
        }

        // Remove the old rotation view
        if self.subviews.count > 0 {
            self.subviews[0].removeFromSuperview()
        }

        // setup rotationView container
        let rotationView = UIView()
        rotationView.frame = CGRect(origin: CGPointZero, size: CGSize(width: self.bounds.height, height: self.bounds.width))
        rotationView.userInteractionEnabled = true
        self.addSubview(rotationView)

        // transform rotationView (so that it covers the same frame as self)
        rotationView.transform = translateRotateFlip()

        // add view
        view.frame = rotationView.bounds
        rotationView.addSubview(view)

    }

    func translateRotateFlip() -> CGAffineTransform {

        var transform = CGAffineTransformIdentity

        // translate to new center
        transform = CGAffineTransformTranslate(transform, (self.bounds.width / 2)-(self.bounds.height / 2), (self.bounds.height / 2)-(self.bounds.width / 2))
        // rotate counterclockwise around center
        transform = CGAffineTransformRotate(transform, CGFloat(-M_PI_2))
        // flip vertically
        transform = CGAffineTransformScale(transform, -1, 1)

        return transform
    }

}

Problem

I noticed that the custom view loads very slowly. I'm new to Xcode Instruments so I watched the helpful videos Debugging Memory Issues with Xcode and Profiler and Time Profiler.

After that I tried finding the issue in my own project. It seems like no matter whether I use the Time Profiler or Leaks or Allocations tools, they all show that my class init method is doing too much work. (But I kind of knew that already from the slow load time before.) Here is a screen shot from the Allocations tool:

I didn't expand all of the call tree because it wouldn't have fit. Why are so many object being created? When I made a three layer custom view I knew that it wasn't ideal, but the number of layers that appears to be happening from the call tree is ridiculous. What am I doing wrong?

Answer 1

You shouldn't add or delete any subview inside layoutSubviews, as doing so triggers a call to layoutSubviews again.

Create your subview when you create your view, and then only adjust its position in layoutSubviews rather than deleting and re-adding it.