What's the Equivalent to String.Localizedstringwithformat(_:_:) for Swiftui's Localizedstringkey

SwiftUI Text and LocalizedStringKey with parameter

Use this extension

extension String {
    public func localized(with arguments: [CVarArg]) -> String {
        return String(format: NSLocalizedString(self, comment: ""), locale: nil, arguments: arguments)
    }
}

Usage :

Text(LocalizationWrapper.helloWorldWithParameter.localized(with: [name]))

Also, This approach is correct

static func helloWithParameter(parameter: String) -> LocalizedStringKey {
    return "helloWorld \(parameter)"
}

SwiftUI Localization and Enums

The answer is much simpler than writing extensions and doing complicated work. Instead of writing a static let, when a variable is present you write a static func. This all takes place in the LocalizationString.swift file's enum and looks like this:

static func testText(name: String) -> LocalizedStringKey { LocalizedStringKey("TEST_TEXT \(name)") }

To use this in your view:

Text(LocalizationStrings.testTest(name: varname))

If you need more variables, just add them into the function.

How to get string value from LocalizedStringKey?

I think it's because SwiftUI is not mean't to do localization from code behind, all localization must happen in view declaration.

However there's a way to achieve that via extensions methods :

extension LocalizedStringKey {

    /**
     Return localized value of thisLocalizedStringKey
     */
    public func toString() -> String {
        //use reflection
        let mirror = Mirror(reflecting: self)
        
        //try to find 'key' attribute value
        let attributeLabelAndValue = mirror.children.first { (arg0) -> Bool in
            let (label, _) = arg0
            if(label == "key"){
                return true;
            }
            return false;
        }
        
        if(attributeLabelAndValue != nil) {
            //ask for localization of found key via NSLocalizedString
            return String.localizedStringWithFormat(NSLocalizedString(attributeLabelAndValue!.value as! String, comment: ""));
        }
        else {
            return "Swift LocalizedStringKey signature must have changed. @see Apple documentation."
        }
    }
}

Sadly you must use Reflection to achieve that as key has an internal level of protection in LocalizedStringKey, use at your own risks.

Use asis :

let s = l10n.helloWorld.toString();

How to use interpolation with strings that rely on automatic grammar agreement?

I was actually very close with this piece of code:

Text("\(String(localized: String.LocalizationValue("Subscription period: \(value) \(unit)"))) free")

But using String(localized:) isn't correct. I guess it's because automatic grammar agreement uses markdown, which is the prerogative of AttributedString. We should use AttributedString(localized:). But even then, it's not going to inflect because apparently there is a bug in Foundation. But once it gets patched, it will work like a charm.

Here is the correct solution:

func freeTrialDuration() -> Text {
    // Use plain string.
    let duration: String = "^[\(value) ^[\(unit.lowercased())](grammar: { partOfSpeech: \"noun\" })](inflect: true)"
    // Use the following way to get the localized string.
    let localizedDuration = AttributedString(localized: String.LocalizationValue(duration))
    
    return Text("\(localizedDuration) free")
}

% symbol in an NSLocalizedString

I think the problem is not with the NSLocalizedString, but with NSLog's interpretation of % symbol. If you pass a format string to NSLog, and put the string that you would like to show as an object parameter, the percentage sign % should survive:

NSLog(@"%@", [NSString stringWithFormat:NSLocalizedString(@"KEY", nil),80.1]);