Category Archives: Programming

Git Config Email String

This is about a simple problem that is obvious after the fact. I was having an issue with my commits on github.com not being linked to my github account. It seemed like I had set everything up (git email configured locally & e-mail set in my github.com account), but it wasn’t working.

On a mac, you probably know you can set your git user e-mail this way:

git config --global user.email name@domain.com

Following the github guide (https://help.github.com/articles/setting-your-commit-email-address-in-git/), I included quotes when setting my git config email.

git config --global user.email "name@domain.com"

It turns out that was a mistake for me since my commits were being associated with “name@domain.com” instead of name@domain.com. Note: the inclusion vs exclusion of quote characters.

After running the git config command above without quotes, I was able to properly link my commits on github to my github user profile.

Intro to Computer Vision

I’m new to computer vision and a lot of the basic concepts are very interesting. As an iOS developer, my interests comes from using CoreML & Apple’s Vision in apps to improve the user experience.

Two common tasks are classification and object detection. Classification allows you to detect dominant objects present in an image. For example, classification can tell you that photo is probably of a car.

Object detection is much more difficult since it not only recognizes what objects are present, but also detects where they are in the image. This means that object detection can tell you that there is probably a car within these bounds of the image.

What’s important is that the machine learning model runs in an acceptable amount of time. Either asynchronous in the background or in real time. Apple provides a listing of sample models for classification at https://developer.apple.com/machine-learning/.

For real time object detection, TinyYOLO is an option, even if the frame rate is not near 60 fps today. Other real time detection models like YOLO or R-CNN are not going to provide a sufficient experience on mobile devices today.

One other interesting thing I came across is the PASCAL Visual Object Classes (VOC). These are common objects used for benchmarking object classification.

For 2012, the twenty object classes that have been selected were:

  • Person: person Animal: bird, cat, cow, dog, horse, sheep
  • Vehicle: aeroplane, bicycle, boat, bus, car, motorbike, train
  • Indoor: bottle, chair, dining table, potted plant, sofa, tv/monitor

These are common objects used to train classification models.

Computer vision used with machine learning has a tremendous amount of potential. Whether used with AR or other use cases, they can provide a compelling user experience beyond Not Hotdog.

How to use child View Controllers in Swift 4.0 programmatically

I’ve just released my Learn to read Korean app for iPhone. It uses a number of child View Controllers in the home screen. While child View Controllers are not a new thing, it was a new experience for me, and I greatly recommend them to reduce the clutter of your View Controllers.

Here’s a photo of my home screen:

The main view controller consists of a vertical UIScrollView and multiple horizontal scrolling UICollectionViews below. While it’s possible to do it all in one massive View Controller, it’s much better to delegate UICollectionView events to their individual child View Controllers.

The good news is that using child UIViewControllers is super easy. You can use your Storyboard or do it programmatically in your UIViewController files. I opted for the latter as I find it easier to reproduce across Xcode projects.

All you need to do to add a child View Controller is below. I included an optional constraints section.

// Create child VC
let childVC = UIViewController()

// Set child VC
self.addChildViewController(childVC)

// Add child VC's view to parent
self.view.addSubview(childVC.view)

// Register child VC
childVC.didMove(toParentViewController: self)

// Setup constraints for layout
childVC.view.translatesAutoresizingMaskIntoConstraints = false
childVC.view.topAnchor.constraint(equalTo: heroView.bottomAnchor).isActive = true
childVC.view.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
childVC.view.widthAnchor.constraint(equalTo: self.view.widthAnchor).isActive = true
childVC.view.heightAnchor.constraint(equalToConstant: height).isActive = true

With multiple child VCs (each handling their own UICollectionView events), the code base becomes manageable. In each child View Controller, you can handle customization, such as background color, UILabels, UIButtons, etc.

Another tip I have is to use the UIView’s convert(_:to:) method as necessary. You may need to get the child subview’s position relative to your parent View Controller’s view (such as for an UIViewControllerTransitioningDelegate). The code for that is simple too:

// contrived example label in Child VC to get parent frame
let label = UILabel()
let childViewFrame = label.frame
let frameInParent = label.convert(childViewFrame, to: parentVC.view)

That’s all I wanted to share for today. Don’t be afraid of using child View Controllers to break up your massive View Controllers!

Vertically Scrolling UIImage programmatically

Working on a small side project, I wanted to display images in my view controller view at full device width in a vertical scrolling view. Sounds simple right? The good news is that it is. While you may want to use UITableView for more control, using UIStackView is a simpler way to get up and running fast.

For my sample code, I opted to do it programmatically as it’s easier to copy & paste code than explain what constraints to add in Xcode. Also note that the code presented here is a proof of concept, quick and dirty example (not intended for production).

The steps are easy to understand:

  1. Add a scroll view to your view
            self.scrollView = UIScrollView()
            scrollView.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(scrollView)
    
            scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
            scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
            scrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor).isActive = true
            scrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor).isActive = true
  2. Add a stack view to your scroll view
            self.stackView = UIStackView()
            stackView.translatesAutoresizingMaskIntoConstraints = false
            stackView.axis = .vertical
            stackView.spacing = 23.0
            scrollView.addSubview(stackView)
    
            scrollView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[stackView]|", options: NSLayoutFormatOptions.alignAllCenterX, metrics: nil, views: ["stackView": stackView]))
            scrollView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[stackView]|", options: NSLayoutFormatOptions.alignAllCenterX, metrics: nil, views: ["stackView": stackView]))
  3. Add images to your stack view
    stackView.addArrangedSubview(image(filename: "photo1"))

For the full code, read the ViewController on GitHub

Hope this helps you if you’re trying to throw together a quick prototype of vertically scrolling images in iOs.

Prior Inclination

Earlier this year, Alex Honnold scaled El Capitan without ropes. That was an impressive & dangerous feat by Alex.

What stuck with me is this quote about Alex from Tommy Caldwell:

Alex once told me that he had never fallen completely unexpectedly—meaning without at least some prior inclination that it could happen.

That is amazing and shows that Alex is simply operating at a higher level. I would make the blanket generalization that most climbers have fallen while climbing without anticipating it.

Why this sticks out to me is when I apply it to other fields. Outdoor climbing can easily be a life or death ordeal. Software generally is not life or death during development.

Can you imagine a programmer who writes code that doesn’t crash without the programmer having some prior inclination? That sounds impossible right? Or a slow development cycle.

I’m not saying that programmers need to be able to anticipate every crash ever. But if someone were able to never have their code crash without prior inclination, that’s awesome.

Supporting the iPhone X with Storyboard

There are a ton of guides out there for updating your app(s) to support the iPhone X.

If you create your view programmatically, you can use iOS 11’s safeAreaLayoutGuide. If your app targets iOS 10 or below, you can use the availability condition, #available().

With the Storyboard, one thing I appreciate from Apple is making the safe area layout guide backwards deployable.

Apple told us in WWDC 2017 Session 412 that Storyboards using safe areas are backwards deployable. This means you can switch to using the safe area layout guide in Interface Builder even if you still target iOS 10 and older.

via https://useyourloaf.com/blog/safe-area-layout-guide/

I don’t always use the storyboard for my layouts, but for apps that I need to update, this backwards deployability helps a lot.

CLI Cut Visual Option

Something I came across recently was command line text manipulation with a CSV. The way that the list option is passed in is cool.

For demonstration purposed, we have a contrived text document “dummy.txt” that happens to be delimited by the % character. The contents inside the file are:

name%car%temp%color
john%honda%fair%blue
tom%benz%fair%red
ed%bmw%cold%green

To get the first column of data, you can run

cut -d% -f1 dummy.txt

which gives you:

name
john
tom
ed

If you wanted to save the output, the standard command line “>” comes in handy.

To get the columns up to (and including the) 2nd column, you can run

cut -d% -f-2 dummy.txt

which gives you:

name%car
john%honda
tom%benz
ed%bmw

To get the 2nd & 3rd columns, inclusive, you can run

cut -d% -f2-3 dummy.txt

which gives you:

car%temp
honda%fair
benz%fair
bmw%cold

To get the 3rd column onward to the last column, you can run

cut -d% -f3- dummy.txt

which gives you:

temp%color
fair%blue
fair%red
cold%green

The examples above are just for this demo, but I think the hyphen syntax in the list fields option is easy to learn and visually clear (for a CLI interface).

Multiple UIDynamicAnimators

In past apps, I tended to have one UIDynamicAnimator in my ViewController and that was that. UIDynamicAnimator allows you to use UIDynamics / effects on your UIViews.

The issue that I ran into was that removeBehavior(_:), which “Removes a specified dynamic behavior from a dynamic animator“, didn’t seem to work. I would keep track of specific UIDynamicBehavior instances and pass them as the argument for removeBehavior(_:) but it didn’t appear to remove the behavior.

What does work is calling removeAllBehaviors() on the UIDynamicAnimator. This is fine if you only have one UIView. But most likely, you have multiple UIViews & behaviors. Calling remove all on the only animator isn’t a good idea. That could leave UIViews frozen out of place.

Recently, I released a fun weekend app, Fun Faces. Browsing stack overflow, it occurred to me to use multiple UIDynamicAnimators. One for each UIView I wanted to animate. This worked for my use case, where calling removeAllBehaviors() doesn’t interrupt the other UIView’s behaviors (if any).

Using multiple UIDynamicAnimators isn’t an answer if you have multiple UIViews under the same animator with UICollisionBehavior or other effects that let the UIViews interact with each other.

Using CoreMotion deviceMotion to keep image level example (Xcode 8.3, Swift 3.1)

I’ve been playing around with CoreMotion since it is frankly so cool. I’ve followed NSHipster’s CMDevice​Motion post, but I made some changes to use the latest Swift v3.1. Below is sample code for using both the gyroscope and accelerometer to keep an image level when you rotate your phone.

//
//  ViewController.swift
//
//  Created by Rex on 4/22/17.
//

import UIKit
import CoreMotion

class ViewController: UIViewController {

    let interval = 0.01
    let imageFilename = "bg.jpg"
    let imageWidth = CGFloat(800)
    let imageHeight = CGFloat(1200)
    
    let manager = CMMotionManager()
    var imageView: UIImageView?

    override func viewDidLoad() {
        super.viewDidLoad()

        guard manager.isDeviceMotionAvailable else { return }
        
        setImageView()
        
        manager.deviceMotionUpdateInterval = interval
        let queue = OperationQueue()
        
        manager.startDeviceMotionUpdates(to: queue, withHandler: {(data, error) in
            guard let data = data else { return }
            let gravity = data.gravity
            let rotation = atan2(gravity.x, gravity.y) - .pi

            OperationQueue.main.addOperation {
                self.imageView?.transform = CGAffineTransform(rotationAngle: CGFloat(rotation))
            }
        })
    }
    
    func setImageView() {
        if let img = UIImage(named: imageFilename) {
            let iv = UIImageView(image: img)

            // center the image
            let x = (self.view.frame.width/2)-(imageWidth/2)
            let y = (self.view.frame.height/2)-(imageHeight/2)
            iv.frame = CGRect(x: x, y: y, width: imageWidth, height: imageHeight)
            
            self.view.addSubview(iv)
            self.imageView = iv
        }
    }
    
}

The setup is simple. Create a new Single View Application project in Xcode. You’ll need to add a JPG to the Assets.xcassets folder in the project. Replace the Viewcontroller with the code below and make sure to update the image filename, width, and height constants.

The code hopefully is straightforward. We make sure the CMMotionManager’s device motion is available. Then, we add the imageview (as the only UIView element we’re adding to the screen). We use an OperationQueue to process the rotation calculation off the main queue. Then we update the imageview with a transform on the main queue.

iOS 10 Locales and Currency Symbols – Sample App

While working on adding localization to my tip calculator, one thing that seems obvious in retrospect is the difference between a device’s language & region. iOS lets you set the language & region separately. For example, you might want to read text in English, but you could be in Asia. This is relevant to tipping since you could travel to a country where tipping is expected, but the country your phone’s language is associated with doesn’t traditionally tip.

While exploring locales and currency symbols, I whipped together a basic demo app that lets you scroll between all the known locales and their currency symbol in iOS 10. This is pretty useful since you can quickly see what the currencySymbol is for each known iOS locale.

Below is the full implementation of very hacked together (quick and dirty) code. All you need to do:

  • Create new Single View Application project in Xcode
  • Replace the ViewController.swift with below (written for Swift 3)
  • Run the app in Xcode
import UIKit

class ViewController: UIViewController, UITableViewDelegate {
    
    let cellIdentifier = "Cell"
    let currentLocaleHeight = CGFloat(80)
    
    let locales = Locale.availableIdentifiers.sorted { $0.localizedCaseInsensitiveCompare($1) == ComparisonResult.orderedAscending }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let tableView: UITableView = UITableView()
        tableView.frame = CGRect(x: 0, y: currentLocaleHeight, width: view.frame.width, height: view.frame.height)
        tableView.dataSource = self
        tableView.delegate = self
        
        self.view.addSubview(tableView)
        
        addCurrentLocaleLabel()
    }
    
    func addCurrentLocaleLabel() {
        let local = Locale.current.identifier
        
        let width = view.frame.width
        let label = UILabel(frame: CGRect(x: 0, y: 0, width: width, height: currentLocaleHeight))
        label.text = "Current locale: " + local
        label.textAlignment = .center
        view.addSubview(label)
    }
    
}

extension ViewController: UITableViewDataSource {
    
    func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return locales.count
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = UITableViewCell(style: .value1, reuseIdentifier: cellIdentifier)
        
        let localeString = locales[indexPath.row]
        
        let numberFormatter = NumberFormatter()
        numberFormatter.locale = Locale(identifier: localeString)
        
        cell.textLabel?.text = localeString
        cell.detailTextLabel?.text = numberFormatter.currencySymbol
        
        return cell
    }

}

Note that the “¤” symbol means the currency is unspecified.