SwiftUI: formatting decimals in Text view

To format a decimal number in a SwiftUI Text view, pass a specifier parameter in the string interpolation. Text("\(age, specifier: "%.0f")") shows a Double like 34.000000 as a clean 34.

Let’s see where the problem comes from, and how the specifier fixes it.

Why does the number show as 34.000000?

When we use the Slider view to select a value, we have to bind it to a Double. Even with a step value of 1, which means we can only select integer values, the state is still a Double. And when we interpolate a Double in a Text view, SwiftUI prints all its decimal digits:

struct ContentView: View {
    @State private var age: Double = 0
    
    var body: some View {
        Form {
            Slider(value: $age, in: 0...100, step: 1)
            Text("\(age)")
        }
    }
}

The specifier parameter

When we interpolate the value of age in the Text view, we can provide an additional parameter called specifier.

This specifier lets us use a string format specifier, the same ones used by String(format:). You can look up the available options in the Apple documentation for String.

In our case, we can use %.0f:

Text("\(age, specifier: "%.0f")")

%f formats a floating point number, and the .0 part means zero digits after the decimal point.

See? Now we get 20 instead of 20.000000:

Other useful specifiers

Change the digit after the dot to control the decimals shown. Two decimals work well for prices:

Text("\(price, specifier: "%.2f")") //34.00

Notice that the specifier rounds the value. With %.0f, a value of 34.6 displays as 35, not 34.

The value is still a Double

One thing to be careful with: the specifier only changes how the number is displayed. The age state is still a Double behind the scenes.

If you later send that value to an API or save it, it goes out as a floating point number. When you need an actual integer, convert it explicitly with Int(age) at that point. The formatting in the Text view won’t do it for you.