dateFormat 中的错误返回 nil [英] Error in dateFormat returns nil

问题描述

作为练习 Objective-C 的练习，我将 Swift 代码转换为 Objective-C.转换了 1.5k 行后，我发现自己在过去的几天里被最后一期屏蔽了.

As an exercise to practice Objective-C, I am converting Swift code to Objective-C. After 1.5k lines converted, I find myself blocked for the past few days on one last issue.

在我的 TableViewController 的几个单元格中，描述标签根本没有出现.我检查了我的代码，似乎传递给单元格的字符串实际上是空的或 nil.

In a few cells of my TableViewController, the description labels don't appear at all. I checked my code, and it seems the strings that are passed to the cells are actually empty or nil.

我似乎在转换将日期返回到我的单元格的 Swift 代码时犯了语法错误.我犯了什么错误导致日期为零?

I seem to have made a syntax error in converting the Swift code that returns the date to my cells. What error have I made that makes the date nil?

...

NSDate const *now = [[NSDate alloc] init];
NSDate *date = [[NSDate alloc] init];

self.sections =  [[NSMutableArray<NSString *> alloc]init];
self.items = [[NSMutableArray<NSMutableArray<TableItem *> *> alloc]init];
self.sectionItems = [[NSMutableArray<TableItem *> alloc]init];

...

这是没有正确加载的单元格数据(空字符串被传递给theDescription):

This is the cell data that doesn't load correctly (empty strings are passed to theDescription):

anItem = [[TableItem alloc ]initWithTitle: @"Custom: dd MMM yyyy HH:mm:ss" theDescription: [NSString stringWithFormat:@"%@", [now toString: [DateFormat CustomDateFormat:@"dd MMM yyyy HH:mm:ss"]]]];
        [_sectionItems addObject: anItem];

//theDescription should be: @"25 April 2016 15:04:57" after this ^, but is actually nil or @""

anItem = [[TableItem alloc ]initWithTitle: @"ISO8601(Year)" theDescription: [NSString stringWithFormat:@"%@", [now toString: [DateFormat ISODateFormat: ISOFormatYear]]]];
        [_sectionItems addObject: anItem];

//theDescription should be: @"2016" after this ^, but is actually nil or @""

这里是我认为我犯了错误的地方:

Here's where I think I've made a mistake:

原始 Swift 语法:

Original Swift syntax:

toString() 函数

toString() function

 case .ISO8601(let isoFormat):
        dateFormat = (isoFormat != nil) ? isoFormat!.rawValue : ISO8601Format.DateTimeMilliSec.rawValue
        zone = NSTimeZone.localTimeZone()

我尝试了什么:

else if([format.dateFormatType compare: ISO8601DateFormatType] == NSOrderedSame) {
    NSString *isoFormat = ISO8601DateFormatType;
    dateFormat =  (isoFormat != nil) ? isoFormat : ISOFormatDateTimeMilliSec;
    zone = [NSTimeZone localTimeZone];
}

推荐答案

问题出在这一行:

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

dateFormat 是 @"Custom"，因为它在这里设置:

dateFormat is @"Custom", as it was set here:

else if([format.dateFormatType compare: CustomDateFormatType] == NSOrderedSame) {
    NSString *string = CustomDateFormatType;
    dateFormat = string;
}

这被传递到您的 NSDateFormatter 构造函数中:

This is passed into your NSDateFormatter constructor here:

formatter.dateFormat = format;

@"Custom" 不是有效的日期格式字符串.相反，传入 format.formatDetails:

@"Custom" is not a valid date format string. Instead, pass in format.formatDetails:

NSDateFormatter *formatter = [NSDate formatter : format.formatDetails : [NSTimeZone localTimeZone] : [NSLocale currentLocale]];

我应该注意，在 Objective-C 中不使用命名参数会使您的代码更难阅读.

I should note that not using named arguments in Objective-C makes your code much harder to read.

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