如何将此 Swift 语法转换为 Objective-C？

Question

我正在将 Swift 库转换为 Objective-C 作为练习。

如何将其转换为 Objective-C ？

let formatter = NSDate.formatter(format: dateFormat)

我试过了：

NSDateFormatter *formatter = [NSDate formatterWithFormat : dateFormat];

也试过这个：

NSDateFormatter *formatter = [NSDate formatterWithFormat : dateFormat : [NSTimeZone localTimeZone] : [NSLocale currentLocale]];

也试过这个：

NSDateFormatter *formatter = [NSDate formatter : dateFormat : [NSTimeZone localTimeZone] : [NSLocale currentLocale]];

错误：不知道选择器“formatterWithFormat:”或“formatter :::”的类方法

更多上下文：

+ (NSDateFormatter *) formatter : (NSString *) format  : (NSTimeZone*) timeZone  : (NSLocale *) locale {
    format = DefaultFormat;
    timeZone = [NSTimeZone localTimeZone];
    locale = [NSLocale currentLocale];
    NSString *hashKey = [NSString stringWithFormat:@"%lu%lu%lu", (unsigned long)format.hash, (unsigned long)timeZone.hash, (unsigned long)locale.hash];
    NSMutableDictionary *formatters = [NSDate sharedDateFormatters];
    NSDateFormatter *cachedDateFormatter = formatters[hashKey];
    if (cachedDateFormatter != nil) {
        return cachedDateFormatter;
    }
    else {
        NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
        formatter.dateFormat = format;
        formatter.timeZone = timeZone;
        formatter.locale = locale;
        formatters[hashKey] = formatter;
        return formatter;
    }
}

中间有一些随机文本，所以我可以添加更多代码...

+ (NSDateFormatter *)formatter:(NSDateFormatterStyle)dateStyle timeStyle:(NSDateFormatterStyle)timeStyle relativeDateFormatting:(BOOL)doesRelativeDateFormatting timeZone:(NSTimeZone *)timeZone locale:(NSLocale *)locale {
    timeZone = [NSTimeZone localTimeZone];
    locale = [NSLocale currentLocale];
    NSString *hashKey = [NSString stringWithFormat:@"%lu%lu%lu%lu%lu", (unsigned long)dateStyle, (unsigned long)timeStyle, (unsigned long)doesRelativeDateFormatting, (unsigned long)timeZone.hash, (unsigned long)locale.hash];
    NSMutableDictionary *formatters = [NSDate sharedDateFormatters];
    NSDateFormatter *cachedDateFormatter = formatters[hashKey];
    if (cachedDateFormatter != nil) {
        return cachedDateFormatter;
    }
    else {
        NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
        formatter.dateStyle = dateStyle;
        formatter.timeStyle = timeStyle;
        formatter.doesRelativeDateFormatting = doesRelativeDateFormatting;
        formatter.timeZone = timeZone;
        formatter.locale = locale;
        formatters[hashKey] = formatter;
        return formatter;
    }
}

原始 Swift 代码：

private class func formatter(format format:String = DefaultFormat, timeZone: NSTimeZone = NSTimeZone.localTimeZone(), locale: NSLocale = NSLocale.currentLocale()) -> NSDateFormatter {
            let hashKey = "\(format.hashValue)\(timeZone.hashValue)\(locale.hashValue)"
            var formatters = NSDate.sharedDateFormatters()
            if let cachedDateFormatter = formatters[hashKey] {
                return cachedDateFormatter
            } else {
                let formatter = NSDateFormatter()
                formatter.dateFormat = format
                formatter.timeZone = timeZone
                formatter.locale = locale
                formatters[hashKey] = formatter
                return formatter
            }
        }

中间有一些随机文本，所以我可以添加更多代码...

private class func formatter(dateStyle dateStyle: NSDateFormatterStyle, timeStyle: NSDateFormatterStyle, doesRelativeDateFormatting: Bool, timeZone: NSTimeZone = NSTimeZone.localTimeZone(), locale: NSLocale = NSLocale.currentLocale()) -> NSDateFormatter {
        var formatters = NSDate.sharedDateFormatters()
        let hashKey = "\(dateStyle.hashValue)\(timeStyle.hashValue)\(doesRelativeDateFormatting.hashValue)\(timeZone.hashValue)\(locale.hashValue)"
        if let cachedDateFormatter = formatters[hashKey] {
            return cachedDateFormatter
        } else {
            let formatter = NSDateFormatter()
            formatter.dateStyle = dateStyle
            formatter.timeStyle = timeStyle
            formatter.doesRelativeDateFormatting = doesRelativeDateFormatting
            formatter.timeZone = timeZone
            formatter.locale = locale
            formatters[hashKey] = formatter
            return formatter
        }
    }

Answer 1

您的语法转换在语法上是正确的。

但是，NSDate 不提供名为formatterWithFormat: 或formatter 的静态方法；您正在翻译的代码似乎有一个 extension 方法。你需要找到那个方法，然后翻译它。

注意：我强烈建议反对将其作为NSDate 的扩展，因为它属于类层次结构的NSDateFormatter 一侧。

Answer 2

根据您的所有更新，您的 Objective-C 代码和 Swift 代码之间的主要区别在于 Swift 函数为参数提供了默认值。这允许您使用零个或多个参数调用函数（在这种情况下）。

由于 Objective-C 不支持默认参数值，因此您需要为每个参数传递一个值。

方法：

+ (NSDateFormatter *) formatter : (NSString *) format  : (NSTimeZone*) timeZone  : (NSLocale *) locale {
}

需要调用为：

[WhateverClassThisIs formatter:someFormat :someTimeZone :someLocale];

请注意由于您没有命名所有参数而导致的丑陋语法（就像我在上一个问题中展示的那样。

您还需要删除添加的行，以便在方法开始时为这些参数赋值。