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];

还试过这个：

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

还试过这个：

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

错误：没有知道选择器的类方法＆＃34; formatterWithFormat：＆＃34;或＆＃34; formatter :::＆＃34;

更多背景信息：

+ (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;
    }
}

介于两者之间的随机文字，所以我会添加更多代码......

+ (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
            }
        }

介于两者之间的随机文字，所以我会添加更多代码......

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扩展名方法。您需要找到该方法，然后翻译它。

注意：我强烈建议反对使其成为NSDate的扩展名，因为它属于类层次结构的NSDateFormatter方。

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函数为参数提供默认值。这允许您使用零个或多个参数调用函数（在本例中）。

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 {
}

需要被称为：

[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所显示的那样。

您还需要删除添加的行，以便在方法开头为这些参数赋值。

如何将这个Swift语法转换为Objective-C？

2 个答案: