CODEWITHSUNDEEP
swiftui
arakweker
arakweker

Reputation: 1635

Error Cannot use instance member 'xxx' within property initializer

26-07-19

I'll update my code as I'm making progress watching the WWDC video's. My data model is:

struct Egg: Identifiable {
    var id = UUID()
    var thumbnailImage: String
    var day: String
    var date: String
    var text: String
    var imageDetail: String
    var weight: Double
}

#if DEBUG
let testData = [

    Egg(thumbnailImage: "Dag-1", day: "1.circle", date: "7 augustus 2019", text: "Kippen leggen iedere dag een ei.", imageDetail: "Day-1", weight: 35.48),

    Egg(thumbnailImage: "Dag-2", day: "2.circle", date: "8 augustus 2019", text: "Kippen leggen iedere dag een ei.", imageDetail: "Day-2", weight: 35.23),

    Egg(thumbnailImage: "Dag-3", day: "3.circle", date: "9 augustus 2019", text: "Kippen leggen iedere dag een ei.", imageDetail: "Day-3", weight: 34.92)

Etc, etc
]

I've a TabbedView, a ContentView, a ContentDetail and a couple of other views (for settings etc). The code for the ContentView is:

struct ContentView : View {
    var eggs : [Egg] = []

    var body: some View {
        NavigationView {
            List(eggs) { egg in
                EggCell(egg: egg)
            }
            .padding(.top, 10.0)
            .navigationBarTitle(Text("Egg management"), displayMode: .inline)
        }
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView(eggs: testData)
    }
}
#endif

struct EggCell : View {
    let egg: Egg

    var body: some View {

        return NavigationLink(destination: ContentDetail(egg: egg)) {

            ZStack {

                HStack(spacing: 8.0) {

                    Image(egg.thumbnailImage)
                        .resizable()
                        .aspectRatio(contentMode: .fit)
                        .padding(.leading, -25)
                        .padding(.top, -15)
                        .padding(.bottom, -15)
                        .padding(.trailing, -25)
                        .frame(width: 85, height: 61)

                    VStack {
                        Image(systemName: egg.day)
                            .resizable()
                            .frame(width: 30, height: 22)
                            .padding(.leading, -82)

                        Spacer()
                    }
                    .padding(.leading)

                    VStack {
                        Text(egg.date)
                            .font(.headline)
                            .foregroundColor(Color.gray)
                        Text(egg.weight.clean)
                            .font(.title)

                    }

                }
            }
        }
    }
}

extension Double {
    var clean: String {
        return self.truncatingRemainder(dividingBy: 1) == 0 ? String(format: "%.0f", self) : String(format: "%.2f", self)
    }
}

The code for the ContentDetail is:

struct ContentDetail : View {
    let egg: Egg

    @State private var photo = true
    @State private var calculated = false
    @Binding var weight: Double

    var body: some View {

        VStack (alignment: .center, spacing: 10) {

            Text(egg.date)
                .font(.title)
                .fontWeight(.medium)
                .navigationBarTitle(Text(egg.date), displayMode: .inline)

            ZStack (alignment: .topLeading) {

                Image(photo ? egg.imageDetail : egg.thumbnailImage)
                    .resizable()
                    .aspectRatio(contentMode: .fill)
                    .background(Color.black)
                    .padding(.trailing, 0)
                    .tapAction { self.photo.toggle() }

                VStack {

                    HStack {
                        Image(systemName: egg.day)
                            .resizable()
                            .padding(.leading, 10)
                            .padding(.top, 10)
                            .frame(width: 50, height: 36)
                            .foregroundColor(.white)

                        Spacer()

                        Image(systemName: photo ?  "photo" : "wand.and.stars")
                            .resizable()
                            .padding(.trailing, 10)
                            .padding(.top, 10)
                            .frame(width: 50, height: 36)
                            .foregroundColor(.white)

                    }

                    Spacer()

                    HStack {
                        Image(systemName: "arrow.left.circle")
                            .resizable()
                            .padding(.leading, 10)
                            .padding(.bottom, 10)
                            .frame(width: 50, height: 50)
                            .foregroundColor(.white)

                        Spacer()

                        Image(systemName: "arrow.right.circle")
                            .resizable()
                            .padding(.trailing, 10)
                            .padding(.bottom, 10)
                            .frame(width: 50, height: 50)
                            .foregroundColor(.white)

                    }
                }
            }

            Text("the weight is: \(egg.weight) gram")
                .font(.headline)
                .fontWeight(.bold)

            ZStack {

                RoundedRectangle(cornerRadius: 10)
                    .padding(.top, 45)
                    .padding(.bottom, 45)
                    .border(Color.gray, width: 5)
                    .opacity(0.1)

                HStack {

                    Spacer()

                    DigitPicker(digitName: "tens", digit: $weight.tens)
                    DigitPicker(digitName: "ones", digit: $weight.ones)

                    Text(".")
                        .font(.largeTitle)
                        .fontWeight(.black)
                        .padding(.bottom, 10)

                    DigitPicker(digitName: "tenths", digit: $weight.tenths)
                    DigitPicker(digitName: "hundredths", digit: $weight.hundredths)

                    Spacer()

                    }
                }

            Toggle(isOn: $calculated) {
                Text(calculated ? "This weight is calculated." : "This weight is measured.")
            }

            Text(egg.text)
                .lineLimit(2)
                .frame(minWidth: 0, maxWidth: .infinity, alignment: .leading)
                .padding(.leading, 6)

            Spacer()

        }
        .padding(6)

    }
}

#if DEBUG
struct ContentDetail_Previews : PreviewProvider {
    static var previews: some View {
        NavigationView { ContentDetail(egg: testData[0]) }
    }
}
#endif


struct DigitPicker: View {
    var digitName: String
    @Binding var digit: Int

    var body: some View {
        VStack {
            Picker(selection: $digit, label: Text(digitName)) {
                ForEach(0 ... 9) {
                    Text("\($0)").tag($0)
                }
            }.frame(width: 60, height: 110).clipped()
        }
    }
}

fileprivate extension Double {
    var tens: Int {
        get { sigFigs / 1000 }
        set { replace(tens: newValue)  }
    }

    var ones: Int {
        get { (sigFigs / 100) % 10 }
        set { replace(ones: newValue) }
    }

    var tenths: Int {
        get { (sigFigs / 10) % 10 }
        set { replace(tenths: newValue) }
    }

    var hundredths: Int {
        get { sigFigs % 10 }
        set { replace(hundredths: newValue) }
    }

    private mutating func replace(tens: Int? = nil, ones: Int? = nil, tenths: Int? = nil, hundredths: Int? = nil) {
        self = Double(0
            + 1000 * (tens ?? self.tens)
            + 100 * (ones ?? self.ones)
            + 10 * (tenths ?? self.tenths)
            + (hundredths ?? self.hundredths)) / 100.0
    }

    private var sigFigs: Int {
        return Int((self * 100).rounded(.toNearestOrEven))
    }
}

The compiler errors I'm still getting are:

  1. in ContentView, beneath NavigationLink: Missing argument for parameter 'weight' in call
  2. in ContentDetail, at NavigationView: Missing argument for parameter 'weight' in call
  3. in ContentDetail, after #endif: Missing argument for parameter 'weight' in call

25-07-19

The following code is part of a List detail view. The var 'weight' is coming from the List through a 'NavigationLink' statement. In this code I declare it as '35.48', but the NavigationLink fills in its real value.

I want to make an array [3, 5, 4, 8] with the compactMap statement. That works okay in Playground. The values go to 4 different pickers (within a HStack).

import SwiftUI
import Foundation

    struct ContentDetail : View {

        var weight : Double = 35.48
        var weightArray = "\(weight)".compactMap { Int("\($0)") }

        @State var digit1 = weightArray[0] // error
        @State var digit2 = weightArray[1] // error
        @State var digit3 = weightArray[2] // error
        @State var digit4 = weightArray[3] // error

        var body: some View {

            VStack (alignment: .center, spacing: 10) {

                Text(weight)
                    .font(.title)
                    .fontWeight(.medium)

    etc etc

I get an error 'Cannot use instance member 'weightArray' within property initializer; property initializers run before 'self' is available'.

If I use the following code it works fine (for the first list element): 

import SwiftUI
import Foundation

    struct ContentDetail : View {

        var weight : Double = 35.48
        var weightArray = [3, 5, 4, 8]

        @State var digit1 = 3
        @State var digit2 = 5
        @State var digit3 = 4
        @State var digit4 = 8

        var body: some View {

            VStack (alignment: .center, spacing: 10) {

                Text(weight)
                    .font(.title)
                    .fontWeight(.medium)

    etc etc

What is the correct SwiftUI approach and why?

Upvotes: 4

Views: 5382

Answers (1)

rob mayoff
rob mayoff

Reputation: 386038

Indeed, a property initializer cannot refer to another property in the same container. You have to initialize your properties in an init instead.

struct ContentDetail: View {

    var weight: Double
    var weightArray: [Int]

    @State var digit1: Int
    @State var digit2: Int
    @State var digit3: Int
    @State var digit4: Int

    init(weight: Double) {
        self.weight = weight
        weightArray = "\(weight)".compactMap { Int("\($0)") }
        _digit1 = .init(wrappedValue: weightArray[0])
        _digit2 = .init(wrappedValue: weightArray[1])
        _digit3 = .init(wrappedValue: weightArray[2])
        _digit4 = .init(wrappedValue: weightArray[3])
    }

But I suspect you're breaking out the digits because you want to let the user edit them individually, like this:

digit editor screenshot

If that's what you want, you should not have a separate @State property for each digit. Instead, weight should be a @Binding and it should have a separate mutable property for each digit.

First, extend Double to give you access to the digits:

fileprivate extension Double {
    var tens: Int {
        get { sigFigs / 1000 }
        set { replace(tens: newValue)  }
    }

    var ones: Int {
        get { (sigFigs / 100) % 10 }
        set { replace(ones: newValue) }
    }

    var tenths: Int {
        get { (sigFigs / 10) % 10 }
        set { replace(tenths: newValue) }
    }

    var hundredths: Int {
        get { sigFigs % 10 }
        set { replace(hundredths: newValue) }
    }

    private mutating func replace(tens: Int? = nil, ones: Int? = nil, tenths: Int? = nil, hundredths: Int? = nil) {
        self = Double(0
            + 1000 * (tens ?? self.tens)
            + 100 * (ones ?? self.ones)
            + 10 * (tenths ?? self.tenths)
            + (hundredths ?? self.hundredths)) / 100.0
    }

    private var sigFigs: Int {
        return Int((self * 100).rounded(.toNearestOrEven))
    }
}

Then, change ContentDetail's weight property to be a @Binding and get rid of the other properties:

struct ContentDetail: View {
    @Binding var weight: Double

    var body: some View {
        HStack {
            DigitPicker(digitName: "tens", digit: $weight.tens)
            DigitPicker(digitName: "ones", digit: $weight.ones)
            DigitPicker(digitName: "tenths", digit: $weight.tenths)
            DigitPicker(digitName: "hundredths", digit: $weight.hundredths)
        }
    }
}

struct DigitPicker: View {
    var digitName: String
    @Binding var digit: Int

    var body: some View {
        VStack {
            Picker(selection: $digit, label: Text(digitName)) {
                ForEach(0 ... 9) {
                    Text("\($0)").tag($0)
                }
            }.frame(width: 60, height: 110).clipped()
        }
    }
}

Here's the rest of the code needed to test this in a playground, which is how I generated that image above:

import PlaygroundSupport

struct TestView: View {
    @State var weight: Double = 35.48

    var body: some View {
        VStack(spacing: 0) {
            Text("Weight: \(weight)")
            ContentDetail(weight: $weight)
                .padding()
        }
    }
}

let host = UIHostingController(rootView: TestView())
host.preferredContentSize = .init(width: 320, height: 240)
PlaygroundPage.current.liveView = host

Upvotes: 4

Related Questions