LocalizedStringKey

Overview 概要

Initializers for several SwiftUI types – such as Text, Toggle, Picker and others – implicitly look up a localized string when you provide a string literal. When you use the initializer Text("Hello"), SwiftUI creates a LocalizedStringKey for you and uses that to look up a localization of the Hello string. This works because LocalizedStringKey conforms to ExpressibleByStringLiteral.

Types whose initializers take a LocalizedStringKey usually have a corresponding initializer that accepts a parameter that conforms to StringProtocol. Passing a String variable to these initializers avoids localization, which is usually appropriate when the variable contains a user-provided value.

As a general rule, use a string literal argument when you want localization, and a string variable argument when you don’t. In the case where you want to localize the value of a string variable, use the string to create a new LocalizedStringKey instance.

The following example shows how to create Text instances both with and without localization. The title parameter provided to the Section is a literal string, so SwiftUI creates a LocalizedStringKey for it. However, the string entries in the messageStore.today array are String variables, so the Text views in the list use the string values verbatim.

List {
    Section(header: Text("Today")) {
        ForEach(messageStore.today) { message in
            Text(message.title)
        }
    }
}

If the app is localized into Japanese with the following translation of its Localizable.strings file:

"Today" = "今日";

When run in Japanese, the example produces a list like the following, localizing “Today” for the section header, but not the list items.