SwiftUI: the ForEach view

ForEach is how you turn a collection into views in SwiftUI. Give it an array or a range, and it creates one view per item.

For example, here we create 3 Text views that print the numbers from 0 to 2:

ForEach(0..<3) {
    Text("\($0)")
}

$0 is the first argument passed to the closure. Here it’s the current number, so 0, then 1, then 2.

Notice that ForEach is a view, not a loop statement. You can’t write a for loop inside body, but you can put a ForEach there.

On its own it doesn’t decide how the views are arranged. So I embed it in a VStack, otherwise the texts would overlap:

VStack {
    ForEach(0..<3) {
        Text("\($0)")
    }.padding()
}

Notice the padding() modifier on the ForEach. It’s applied to each generated view, so every number gets its own spacing.

ForEach inside a List

The most common place for ForEach is inside a List:

List {
    ForEach(0..<3) {
        Text("\($0)")
    }
}

This is so common that you can drop ForEach and hand the collection to List directly:

List(0..<3) {
    Text("\($0)")
}

Same result, less code. I use the short form when the whole list is one collection, and the explicit ForEach when I need to mix static rows and generated rows in the same list.

Iterating over an array

Those examples used the range 0..<3. Let’s iterate over an array instead:

let fruits = ["Apple", "Pear", "Orange"]

//...

List {
    ForEach(fruits, id: \.self) {
        Text("\($0)")
    }
}

Notice the new parameter: id.

SwiftUI needs a way to tell the items apart. When the array changes, it uses the id to figure out which rows were added, removed, or moved, and animates only those. With a range it doesn’t need help, because each number is already unique.

\.self says “use the value itself as the id”. That works for strings, numbers, and other built-in types, as long as there are no duplicates. Two "Apple" entries would share an id and confuse the list.

When you iterate over your own struct, you have two options. Pass a key path to a unique property, like id: \.isbn. Or make the struct conform to the Identifiable protocol, which means giving it an id property. Then you can drop the parameter and write ForEach(books). That’s the version I use in every real app.