ForEach and Identifiable

Hub › iOS › Beginner › ForEach and Identifiable

Goal

You will render a List from an array of structs by making the struct conform to Identifiable. After this page you will be able to drive a list from any array of data — the last piece the exit artifact needs.

Prerequisites

• Structs
• List

Why Identifiable matters

SwiftUI re-runs body constantly. When a list's data changes, SwiftUI needs to know which row is which — otherwise it can't animate the right row in or out, and it can't tell a "new row" from "the same row with edited text".

It does that by asking each item: "what's your stable ID?". The Identifiable protocol is the contract for that question. Any type that conforms must expose a property called id whose value uniquely identifies it.

The pieces:

• Identifiable — a one-property protocol from Swift's standard library.
• id: UUID — a universally unique 128-bit identifier. UUID() makes a fresh one. This is the lazy, always-correct default.
• ForEach(items) { item in ... } — the SwiftUI loop that turns an array into views. Inside List, ForEach is the standard way to render dynamic rows.

For everything Identifiable can do, see the Swift documentation.

Render a list from an array of structs

Open ContentView.swift in HelloIOS and replace the contents with:

import SwiftUI

struct Habit: Identifiable {
    let id: UUID = UUID()
    let title: String
    let streak: Int
}

struct ContentView: View {
    let habits: [Habit] = [
        Habit(title: "Read", streak: 3),
        Habit(title: "Walk", streak: 7),
        Habit(title: "Hydrate", streak: 1),
        Habit(title: "Sleep early", streak: 0),
    ]

    var body: some View {
        List {
            ForEach(habits) { habit in
                HStack {
                    Text(habit.title)
                    Spacer()
                    Text(String(habit.streak) + " days")
                        .foregroundStyle(.secondary)
                }
            }
        }
        .listStyle(.insetGrouped)
    }
}

#Preview {
    ContentView()
}

The canvas shows four rows. Each row has the habit name on the left and the streak count on the right, separated by Spacer() — a flexible view that takes up all remaining space along the stack's axis.

Read each piece:

• struct Habit: Identifiable — the struct promises an id. Because id is let id: UUID = UUID() with a default, the memberwise initializer doesn't need it as an argument (Swift fills in the default).
• let habits: [Habit] = [...] — a hard-coded array on the view itself. The next tier replaces this with a model object.
• ForEach(habits) { habit in ... } — trailing-closure loop. Because Habit is Identifiable, we did not have to write ForEach(habits, id: \.id) — SwiftUI infers the key path from the protocol.

You now have every piece of the tier exit artifact. The next page assembles it into a clean, ready-to-ship project.

Next → Ship a one-screen list app