Day 16,17, 18, 19 of #100DaysOfSwiftUI

Start 100DaysOfSwiftUI from 2020.Mar.18th.

Day 16, 17, 18, 19: Project 1, part one, two and three (including challenges)
done with 75min.

New findings: many findings
"preview content" is resource for previewing. I just ignored until now...
".keyboardType" is new findings. I have never used, but looks convenient for user.
SegmentedPickerStyle has great UI style.
specifier: is also very interesting.
maybe I miss more convenient modifier of SwiftUI components.

Here is the code.

//
//  ContentView.swift
//  WeSplit
//
//  Created by Tomoaki Yagishita on 2020/03/28.
//  Copyright © 2020 SmallDeskSoftware. All rights reserved.
//

import SwiftUI

struct ContentView: View {
    @State private var checkAmount = ""
    @State private var numberOfPeople = "2"
    @State private var tipPercentage = 2
    let tipPercentages = [10, 15, 20, 25, 0]

    var totalAmountForCheck: Double {
        let tipSelection = Double(tipPercentages[tipPercentage])
        let orderAmount = Double(checkAmount) ?? 0
        
        let tipValue = orderAmount / 100 * tipSelection
        let grandTotal = orderAmount + tipValue
        
        return grandTotal
    }

    
    var totalPerPerson: Double {
        let peopleCount = Double(numberOfPeople) ?? 0
        let tipSelection = Double(tipPercentages[tipPercentage])
        let orderAmount = Double(checkAmount) ?? 0
        
        let tipValue = orderAmount / 100 * tipSelection
        let grandTotal = orderAmount + tipValue
        let amountPerPerson = grandTotal / peopleCount
        
        return amountPerPerson
    }
    
    var body: some View {
        NavigationView {
            Form {
                Section {
                    TextField("Amount", text: $checkAmount)
                        .keyboardType(.decimalPad)
                    TextField("Number of People", text: $numberOfPeople)
                        .keyboardType(.decimalPad)
                }
                Section(header: Text("How much tip do you want to leave?")) {
                    Picker("Tip percentage", selection: $tipPercentage) {
                        ForEach(0 ..< tipPercentages.count) {
                            Text("\(self.tipPercentages[$0])%")
                        }
                    }
                .pickerStyle(SegmentedPickerStyle())
                }
                Section(header: Text("Total amount for the check")) {
                    Text("$\(totalAmountForCheck, specifier: "%.2f")")
                }

                Section(header: Text("Amount per person")) {
                    Text("$\(totalPerPerson, specifier: "%.2f")")
                }
            }.navigationBarTitle("WeSplit")
        }
    }
}

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