Can You Write a Custom View Modifier?

A custom view modifier is how you turn a repeated SwiftUI style into a named, reusable API — and that’s exactly what this interview question is probing.

This one shows up often enough in SwiftUI interviews that it’s worth having ready. It’s not a trick question. When it does come up, interviewers usually want a quick signal: can you move past .padding().background(.red) pasted on every screen, and actually name that look?

Most candidates know modifiers exist. Fewer can build one cleanly under pressure.

What a strong answer looks like

You’re expected to:

1. Conform to ViewModifier
2. Style content inside body
3. Expose a View extension so usage reads like a built-in modifier
4. Explain why — reuse, clarity, one place to change

The code

import SwiftUI

struct PaddedRedBackground: ViewModifier {
    func body(content: Content) -> some View {
        content
            .padding()
            .background(.red)
    }
}

extension View {
    func paddedRedBackground() -> some View {
        modifier(PaddedRedBackground())
    }
}

struct Parent: View {
    var body: some View {
        Text("Hello World")
            .paddedRedBackground()
    }
}

The extension lets you call .paddedRedBackground() instead of typing .modifier(PaddedRedBackground()) every time — so it feels like a normal SwiftUI modifier.