Mobile App Dev 2022W: Assignment 2

This assignment is still being developed.

Questions

When explaining what code does, be sure to explain both the mechanics of what the code does and how that code fits into the overall functionality of the program.

1. [1] Explain how to add this image from Wikipedia to the image list under the name "Boxer".
2. [2] What name is added to the menu if we manually enter a URL and select "Remember Image"? Why? Explain with an example.
3. [2] There is an image URL on line 67. When is this image displayed during normal program operation? Why?
4. [2] If you delete line 28 and instead replace line 20 with "var imageNames = [String] (images.keys)", the program will compile and run. Will it function any differently? Why?
5. [2] Why does the program have both currentAmount and finalAmount for implementing the magnification gesture? Specifically, how does the program behave if we use finalAmount in the onChanged handler and do nothing in the onEnded handler of magnifying?
6. [2] What do each line do in lines 50-53? These implement the action function of the "Remember Image" menu option.
7. [2] The dragging gesture handler (lines 127-137) has both an onChanged and onEnded handler that have exactly the same code in them. What does their code do? How does the program function with just one or the other?
8. [1] How does the program's behavior change if we replace line 90 with ".onTapGesture(count: 3, perform: tapReset)"?
9. [2] Is the images dictionary mutable or immutable? How do you know?
10. [2] When typing in a new URL, when is AsyncImage updated? Does it try loading the URL as you type, or does it wait until the URL is fully entered? Explain briefly.
11. [2] How could you change the program so that the double click zoom command only zooms in three times and on the fourth it goes back to a magnification of 1 (no zoom)? Your solution shouldn't add any new variables.
12. [2] How does the program's behavior change if you move lines 86 and 89 to just before 83? Why?

Code: remotePicViewer2 ContentView.swift

// remotePicViewer2
//
// code for Assignment 2
// COMP 1601 2022W, Carleton University
//
// Anil Somayaji, February 10, 2022
// Code is licenced under the FSF GPLv3 or newer
//
// Note this code is for teaching purposes only.  In particular
// it is not robust and does not handle error conditions properly.
//

import SwiftUI

var images: [String: String] = [
    "Kittens": "https://homeostasis.scs.carleton.ca/~soma/mad-2022w/images/kittens.jpeg",
    "Sad Dog":
        "https://homeostasis.scs.carleton.ca/~soma/mad-2022w/images/roshi.jpeg",
]

@available(macOS 12.0, *)
struct ContentView: View {
    @State private var imageName = "Kittens"
    @State private var theImage = getImage("Kittens")
    @State private var moved = false
    @State private var finalAmount: CGFloat = 1
    @State private var angle = Angle(degrees: 0.0)
    @State private var imageNames = [String] (images.keys)
    
    func resetState() {
        moved = false
        finalAmount = 1
        angle = Angle(degrees: 0.0)
    }
    
    var body: some View {
        VStack {
            Text("Image Viewer")
                .font(.title)
            TextField("Enter an image URL", text: $theImage)
            Menu("Known Images") {
                ForEach(imageNames, id: \.self) {s in
                    Button(s, action: {
                        theImage = getImage(s)
                        resetState()
                    })
                }
                Divider()
                Button("Remember Image", action: {
                    let urlParts = theImage.split(separator: "/")
                    let newName = String(urlParts[urlParts.count - 1])
                    imageNames.append(newName)
                    images[newName] = theImage
                })
            }
            Divider().background(Color.black)
            ActiveImage(theImage: $theImage, imageName: $imageName, moved: $moved, finalAmount: $finalAmount, angle: $angle)
        }
    }
}

func getImage(_ imageName: String) -> String {
    return images[imageName] ?? "https://homeostasis.scs.carleton.ca/~soma/year.jpg"
}

@available(macOS 12.0, *)
struct ActiveImage: View {
    @State private var position = CGPoint(x: 0, y: 0)
    @State private var currentAmount: CGFloat = 0

    @Binding var theImage: String
    @Binding var imageName: String
    @Binding var moved: Bool
    @Binding var finalAmount: CGFloat
    @Binding var angle: Angle
    
    var body: some View {
        GeometryReader {g in
            AsyncImage(url: URL(string: theImage), content: {image in
                image
                    .resizable()
                    .scaledToFit()
                    .position(moved ? position :
                                CGPoint(x: g.size.width / 2,
                                        y: g.size.height / 2))
                    .scaleEffect(finalAmount + currentAmount)
                    .gesture(dragging)
                    .gesture(magnifying)
                    .rotationEffect(self.angle)
                    .onLongPressGesture(perform: tapReset)
                    .onTapGesture(count: 2, perform: zoom)
                    .onTapGesture(count: 1, perform: rotateImage)
            }, placeholder: {
                ProgressView()
                    .position(moved ? position :
                                CGPoint(x: g.size.width / 2,
                                        y: g.size.height / 2))
            })
        }
    }
    
    func zoom() {
        self.finalAmount = self.finalAmount * 2
    }

    func tapReset() {
        self.finalAmount = 1
        self.moved = false
        self.angle = Angle(degrees: 0.0)
    }
    
    func rotateImage() {
        let oldDegrees = self.angle.degrees
        self.angle = Angle(degrees: oldDegrees + 45)
    }

    var magnifying: some Gesture {
        MagnificationGesture().onChanged { amount in
            self.currentAmount = amount - 1
        }
        .onEnded { amount in
            self.finalAmount += self.currentAmount
            self.currentAmount = 0
        }
    }
    
    var dragging: some Gesture {
        DragGesture()
            .onChanged {s in
                self.moved = true
                self.position = s.location
            }
            .onEnded {s in
                self.moved = true
                self.position = s.location
            }
    }
}


struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}