Using user input in SwiftUI to perform calculations

Question

I'm making a school project in which I have to find the weight of a person on different planets, but I am confused about how I should use the input and multiply it by the gravity on each planet.

Also, I am not sure whether or not weight is an int and can be multiplied with another number.

Here is my code:

struct PlanetDetail: View {
    let planet : Planet
    @State var weight = ""

    var body: some View {
        VStack {
            Text(planet.name)
            Text("Gravity on mercury is\(planet.gravity)")
            TextField( "Enter your weight", text:$weight)
            Text("your weight on \(planet.name) is ")
        }
    }
}

Answer 1

You have specified your weight variable like this:

@State var weight = ""

By assigning an empty string (""), you have declared weight to be a String.

In order to multiply this value with an integer, you will need to convert the string value to an integer.

You will also need handle the case where a user could enter non-numeric values into your text input.

Instead, store the weight value as an integer.

You can take care of this by creating a Binding that is used when the user enters a value into the text field. For example:

 @State var weight = 0

    var body: some View {
        let weightProxy = Binding<String>(
            get: { String(format: "%.02f", Int(self.weight)) },
            set: {
                if let value = NumberFormatter().number(from: $0) {
                    self.weight = value.intValue
                }
            }
        )

You would then bind your TextField to weightProxy:

TextField( "Enter your weight", text:$weightProxy)

The best case scenario would be to have a TextField that only accepts numbers. That is a bit more work, but could be a good project to tackle next!