Unit Conversion in SwiftUI - swift

Question

I'm currently working on a unit conversion app, and ran into a problem that I'm still trying to figure how to solve it. The app is supposed to convert one unit to a different unit, and supposed to convert and display new value in the text view every time a unit is converted to a different unit.(meters to kilometers, miles to yards, etc.). I created a computed property called result which handles the conversion, but when I run the code in the simulator and toggle between the units, no changes are displayed to show the units converted successfully. I tried using a guard statement before the calculations since I figured Value is 0 after converting inputNumber to an integer, but that doesn't seem to work. I'm not sure where I went wrong but any help with this would be greatly appreciated. I have attached the code and simulator below.
Thanks.
PS. I have learned how to and can build this app using the measurement functionality provided by Apple, I'm trying to learn how to build it in a different way by basically using math calculations only.
struct ContentView: View {
#State private var inputNumber = ""
#State private var inputUnitValue = 2
#State private var outputUnitValue = 2
#State private var outputValue = ""
let inputUnits = ["Feet", "Meters", "Kilometers", "Yard", "Miles"]
let outputUnits = ["Feet", "Meters", "Kilometers", "Yard", "Miles"]
var result: Double {
var outputType = ""
var inputType = ""
let value = Double(inputNumber) ?? 0
var output = Double(outputValue) ?? 0
var input = Double(inputNumber) ?? 0
guard value > 0 else {
return 0
}
//Converts input value to input unit
switch inputUnits[inputUnitValue] {
case "meters":
input = value * 3.28
case "kilometers":
input = value * 3280.84
case "yards":
input = value * 3
case "miles":
input = value * 5280
case "feet":
input = value * 1
default:
input = value * 3.28
}
//Converts input unit to output unit
switch outputUnits[outputUnitValue] {
case "meters":
output = value / 3.28
case "kilometers":
output = value / 3280.84
case "yards":
output = value / 3
case "miles":
output = value / 5280
case "feet":
output = value / 1
default:
output = value / 3.28
}
return output
}
var body: some View {
NavigationView {
Form {
Section {
TextField("Value", text: $inputNumber)
.keyboardType(.numberPad)
}
Section(header: Text("Input Units")) {
Picker("Input Units", selection: $inputUnitValue) {
ForEach(0 ..< inputUnits.count) {
Text("\(self.inputUnits[$0])")
}
}
.pickerStyle(SegmentedPickerStyle())
}
Section(header: Text("Output Units")) {
Picker("Input Units", selection: $outputUnitValue) {
ForEach(0 ..< outputUnits.count) {
Text("\(self.outputUnits[$0])")
}
}
.pickerStyle(SegmentedPickerStyle())
}
Section (header: Text("output")){
Text("\(result, specifier: "%.2f")")
}
}
.navigationBarTitle("Unit Conversion")
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}

Answer 1

switch is case sensitive. Your inputUnits and outputUnits are capitalized...
let inputUnits = ["Feet", "Meters", "Kilometers", "Yard", "Miles"]
... while your switch conditions are lowercased.
switch inputUnits[inputUnitValue] {
case "meters": /// lowercased
...
}
So, your switch statement always falls through to the default.
To fix, just add .lowercased():
switch inputUnits[inputUnitValue].lowercased() {
switch outputUnits[outputUnitValue].lowercased() {
One more thing: I assume the purpose of your switches are to:
Convert value to a standard feet unit
Convert that feet to the output unit
In this case, inside the second switch, you need to perform calculations using your input variable (which is the input converted to feet) - not value.
To make things less confusing, I've renamed input to inputAsFeet.
var result: Double {
let value = Double(inputNumber) ?? 0
var inputAsFeet = Double(0)
var output = Double(0)
guard value > 0 else {
return 0
}
switch inputUnits[inputUnitValue].lowercased() {
case "meters":
inputAsFeet = value * 3.28
case "kilometers":
inputAsFeet = value * 3280.84
case "yards":
inputAsFeet = value * 3
case "miles":
inputAsFeet = value * 5280
case "feet":
inputAsFeet = value * 1
default:
inputAsFeet = value * 3.28
}
switch outputUnits[outputUnitValue].lowercased() {
case "meters":
output = inputAsFeet / 3.28
case "kilometers":
output = inputAsFeet / 3280.84
case "yards":
output = inputAsFeet / 3
case "miles":
output = inputAsFeet / 5280
case "feet":
output = inputAsFeet / 1
default:
output = inputAsFeet / 3.28
}
return output
}
Result: