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Hi, Swift

I shared this article in our assignment 2 of iOS course class. This keynote is about the Swift and what’s different between Swift, Kotline and Java.

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Part 1

List the new technologies I have learned:

info.plist configuration: How to acquire photo library permission.

<string>I need your permission to save this image to album.</string>

UIBezierPath it’s a very very important class for UIKit,

func triangle(startPoint: CGPoint, translationPoint: CGPoint) -> UIBezierPath {
    let rect = CGRect(x: startPoint.x, y: startPoint.y,
    	 width: translationPoint.x, height: translationPoint.y)
    let trianglePath = UIBezierPath() //create BezierPath object
    // move to point
    trianglePath.move(to: CGPoint(x: rect.minX, y: rect.minY))
    // add line
    trianglePath.addLine(to: CGPoint(x: rect.maxX, y: rect.maxY))
    // add line
    trianglePath.addLine(to: CGPoint(x: (2 * rect.minX - rect.maxX), y: rect.maxY))
    // close start point and last point
    return trianglePath

Linear Bézier curves, Quadratic Bézier curves, Cubic Bézier curves


extension CALayer {
    /// Add border color for view
    var borderUIColor: UIColor {
        set {
            self.borderColor = newValue.cgColor
        get {
            return UIColor(cgColor: self.borderColor!)

Using UIImage.withRenderingMode and tintColor to change UIImage color

It’s quite important to understand that if we can import less images, the app size will be more samll. withRenderingMode and tintColor can help us to achieve that, only using one image to implement many color of this image.

// get an image from assets
let imgOval = UIImage(named: "ic_panorama_fish_eye_48pt")
//Creates and returns a new image object with the specified rendering mode.
let tintOval = imgOval?.withRenderingMode(.alwaysTemplate)
//set it into button
button.setImage(tintOval, for: .normal)
//set button's tintColor
button.tintColor =

Save a photo to Photos

/// save to photos
/// - Parameter view: the view need to save
func saveToPhotos(view:UIView) {
    UIGraphicsBeginImageContext(CGSize(width: view.frame.size.width, height: view.frame.size.height))
    view.drawHierarchy(in: CGRect(x: 0.0, y: 0.0, width: view.frame.size.width, height: view.frame.size.height), afterScreenUpdates: true)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    //Adds the specified image to the user’s Camera Roll album.
    UIImageWriteToSavedPhotosAlbum(image!, self, #selector(image(_:didFinishSavingWithError:contextInfo:)), nil)

/// call back for save image to Photos
/// - Parameters:
///   - image: UIImage
///   - error: Error for that
func image(_ image: UIImage, didFinishSavingWithError error: NSError?, contextInfo: UnsafeRawPointer) {
    if let error = error {
        // we got back an error!
        let ac = UIAlertController(title: "Save error", message: error.localizedDescription, preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
    } else {//tell users save successful
        let ac = UIAlertController(title: "Saved!", message: "Your altered image has been saved to your photos.", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)


UIPanGestureRecognizer, CAShapeLayer, Gesture Recognizer state (began, changed), etc.

Which part did I do well?


  • Reuse Slider: when click from shapes to pan or line, Slider will switch from Opacity to Line width
  • Using only one copy image to change Images color (showed above code)
  • Color buttons don’t need to use images. Using symbol, and then change text color to implement.

Which part I can improve?


In this screenshot, it’s iPhone 5 screen, some components are out of screen edge. Actually, it’s easy to understand, because I constrain all of these components’ size.

The solution is remove these Constraints and make these components Constraints as Horizontally in Container.

There is an article I have written several days ago, it is about Auto Layout, it may some help: Auto Layout for a Calculator

Apple Human Interface Guideline

In terms of Alert to users, some alert’s buttons should be more easy to use, see below picture:


There is an guideline for iOS: Alerts.

iOS app life cycle

core_objects_2x high_level_flow_2x

  • Get data from server-side or Core Data or iCloud.
  • Save data to server-side or Core Data or iCloud.

See: The App Life Cycle

Part 2: Swift, Java and Kotlin

For more detail, please visit Assignment2-keynote