Question

有趣的问题让我感到高兴。

我收到从服务器到设备的字符串时间。然后我将其转换为NSDate。当设备设置为显示24小时时，生活很好。

现在我在设置为12小时的设备上测试它。一切都停止了。日期将返回null

我第一次

 NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
 [dateFormat setDateFormat:@"HH:mm"];
 self.startTime = [dateFormat dateFromString:(NSString *)self.startTime];

完美适用于显示24小时但不是12小时的设备。

然后我尝试了

 NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
 [dateFormat setDateFormat:@"hh:mm"];
 self.startTime = [dateFormat dateFromString:(NSString *)self.startTime];

这项工作正常至中午12点，然后所有日期都返回为空

更新

我也尝试添加“a”但这仍然会导致返回null

 if (startDate == nil)
 {
      NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
      [dateFormat setDateFormat:@"hh:mm a"];
      startDate = [dateFormat dateFromString:(NSString *)self.startTime];
 }

更新2

添加本地，添加：添加全部的ss仍然无法正常工作

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
NSLocale *twelveHourLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
dateFormat.locale = twelveHourLocale;
[dateFormat setDateFormat:@"hh:mm a"];
startDate = [dateFormat dateFromString:(NSString *)self.startTime];

Answer 1

关闭......我认为你需要：

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
[dateFormatter setLocale:locale];
[dateFormatter setDateFormat:@"HH:mm"];
startDate = [dateFormatter dateFromString:(NSString *)self.startTime];

Answer 2

你可以试试这个

    12 to 24 hour format


    NSDateFormatter* df = [[NSDateFormatter alloc] init];
    [df setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"]];
    [df setTimeZone:[NSTimeZone systemTimeZone]];
    [df setDateFormat:@"hh:mm a"];
    NSDate* newDate = [df dateFromString:LocationTrackingStartTime];
    [df setDateFormat:@"HH:mm"];
    newDate = [df stringFromDate:newDate];

   24 to 12 hour format

    NSDateFormatter* df = [[NSDateFormatter alloc] init];
    [df setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"]];
    [df setTimeZone:[NSTimeZone systemTimeZone]];
    [df setDateFormat:@"yyyy-mm-dd hh:mm:ss"];
    NSDate* newDate = [df dateFromString:[df stringFromDate:[NSDate date]]];
    [df setDateFormat:@"hh:mm a"];
    newDate = [df stringFromDate:[NSDate date]];

Answer 3

你必须添加am / pm：

NSLocale *twelveHourLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
dateFormat.locale = twelveHourLocale;
[dateFormat setDateFormat:@"hh:mm: a"];

Answer 4

将24小时格式更改为12小时格式，

    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    //Set 24 hours date format
    dateFormatter.dateFormat = @"HH:mm";

    //Here @"your24hours date string" is your string date with 24 hours format
    NSDate *date = [dateFormatter dateFromString:@"your24hours date string"];

    //Set 12 hours date format
    dateFormatter.dateFormat = @"hh:mm a";
    NSString *strDate = [dateFormatter stringFromDate:date];

    NSLog (@"%@", strDate);

   //Output is in 12 hours date format.

Answer 5

您想再次将NSDate强制转换为NSString再转换为NSDate。首先，您必须将其转换为NSString，而不是强制它！

我也支持12小时和24小时格式，我也没有问题。

Answer 6

NSDateFormatter* df = [[NSDateFormatter alloc]init];

[df setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"]];
[df setTimeZone:[NSTimeZone systemTimeZone]];    
[df setDateFormat:@"MM/dd/yyyy hh:mm a"];

NSDate* newDate = [df dateFromString:strDate4Convert];    
[df setDateFormat:@"MM/dd/yyyy HH:mm:ss"];    
 NSString *newTimeStr = [df stringFromDate:newDate];

Answer 7

   You just need to set the locale to take the am pm format. And everything else as usual.

    NSDateFormatter * df = [[NSDateFormatter alloc]init];
    NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"]; 
    [df setLocale:locale];
    [df setDateStyle:NSDateFormatterNoStyle];
    [df setTimeStyle:NSDateFormatterShortStyle];
    NSLog(@"%@", [df stringFromDate:pickUpDate]);

iOS：从字符串切换12/24小时

7 个答案: