如何通过NumberFormatter以辅币单位显示SKProduct本地化小额单价？

Absolutely! You can pull this off with NumberFormatter—it just takes a bit of targeted configuration to handle both localized currency formatting and the switch to sub-unit display when the unit price is less than one main currency unit. Let me break down exactly how to implement this for your SKProduct bundles.

Step 1: Calculate the Unit Price First #

First, we need to compute the individual unit price by dividing the SKProduct's total price by the number of items in the bundle. Using NSDecimalNumber here is crucial to avoid floating-point precision errors with currency values.

func calculateUnitPrice(for product: SKProduct, bundleItemCount: Int) -> NSDecimalNumber {
    guard bundleItemCount > 0 else { return product.price }
    return product.price.dividing(by: NSDecimalNumber(value: bundleItemCount))
}

Step 2: Configure NumberFormatter for Localized Display #

Next, we'll set up a NumberFormatter that uses the product's priceLocale (critical for matching the user's regional currency preferences) and adds logic to switch between main currency units and sub-units (like pence or cents) when needed.

Here's the full implementation with comments explaining each part:

func formattedUnitPrice(for product: SKProduct, bundleItemCount: Int) -> String? {
    let unitPrice = calculateUnitPrice(for: product, bundleItemCount: bundleItemCount)
    let formatter = NumberFormatter()
    formatter.locale = product.priceLocale
    
    // Get the number of decimal digits used by the currency (most use 2, some like JPY use 0)
    guard let decimalDigits = formatter.locale.object(forKey: .currencyDecimalDigits) as? Int else {
        // Fallback to basic currency formatting if we can't get decimal digits
        formatter.numberStyle = .currency
        return formatter.string(from: unitPrice)
    }
    
    let mainUnitToSubUnitRatio = NSDecimalNumber(decimal: pow(10, decimalDigits))
    let isUnitPriceLessThanMainUnit = unitPrice.compare(NSDecimalNumber.one) == .orderedAscending
    
    if isUnitPriceLessThanMainUnit {
        // Convert the unit price to an integer sub-unit amount (e.g., 0.99 GBP → 99 pence)
        guard let subUnitAmount = unitPrice.multiplying(by: mainUnitToSubUnitRatio).integerValue as NSNumber? else {
            return formatter.string(from: unitPrice)
        }
        
        // Map common currency codes to their sub-unit symbols for accuracy
        let subCurrencySymbols: [String: String] = [
            "GBP": "p",
            "USD": "¢",
            "EUR": "¢",
            "CAD": "¢",
            "AUD": "¢",
            // Add more currencies as needed for your app
        ]
        
        // Use the matching sub-unit symbol, or fall back to a reasonable default
        if let currencyCode = formatter.locale.currencyCode, let subSymbol = subCurrencySymbols[currencyCode] {
            return "\(subUnitAmount)\(subSymbol)"
        } else {
            // Fallback for less common currencies: append lowercase main symbol or just the number
            return "\(subUnitAmount)\(formatter.currencySymbol?.lowercased() ?? "")"
        }
    } else {
        // For prices ≥ 1 main unit, use standard localized currency formatting
        formatter.numberStyle = .currency
        return formatter.string(from: unitPrice)
    }
}

Key Notes & Edge Cases #

• Precision Safety: Using NSDecimalNumber ensures we don't get rounding errors that come with floating-point types like Double when dividing currency values.
• Locale Compatibility: By using the SKProduct's priceLocale, we automatically align with the user's regional settings (e.g., decimal separators, currency symbols).
• Zero-Decimal Currencies: For currencies like Japanese Yen (JPY) that don't use sub-units, the logic will skip the sub-unit check and always use standard currency formatting (since you can't have a price less than 1 JPY for a valid SKProduct).
• Customization: The subCurrencySymbols dictionary can be extended to cover all currencies your app supports, ensuring the most accurate sub-unit symbols for each region.

Example Results #

• For a £9.99 bundle of 10 items (UK locale): Returns 99p
• For a $9.99 bundle of 10 items (US locale): Returns 99¢
• For a $5.00 bundle of 4 items (US locale): Returns $1.25

内容的提问来源于stack exchange，提问作者Ryan Brodie