IOS如何将日期与另一个日期进行比较？

Question

我有一个包含XML数据列表的Web服务。其中一个元素是"UpdateTimeStampGMT"。我已在此元素中检索此参数，当我将其注销以进行检查时，该参数看起来像这样。

 UpdateTimestampGMT = "2015-11-03T01:00:59.503";

但现在的问题是我想利用这个日期来检查这个日期是4天前的日期还是3天前的日期，如果它有效我想要检索块中的其他元素属于正确的日期。

以下是编码：

   int minusThreeDayopenSSLCount = 0;

    int bluecolor = 0;
    NSDate *now = [NSDate date];
    NSDate *threeDaysAgo = [now dateByAddingTimeInterval:-3*24*60*60];
//This is the data when i NSLOG threeDaysAgo: 2015-10-29 09:06:40 +0000

for (NSDictionary *feed in feeds) {
        if ([feed[@"Classification"] isEqualToString:@"Activity Summary - OpenSSL \"HeartBleed\" Scanning"] && [feed[@"UpdateTimestampGMT"] isEqualToString:threeDaysAgo]) {
            minusThreeDayopenSSLCount ++;
        }
    }
 NSLog(@"-3 Total openSSLCount count is (green):  %d",minusThreeDayopenSSLCount);

当我NSLOG

时

minusThreeDayOpenSSLCount 它看起来像这样，这是不正确的

  

- ＆GT; 2015-11-05 17：06：44.443 FYP_IOS_APP [928：444918] -3总openSSLCount计数为（绿色）：0

当我改变

if ([feed[@"Classification"] isEqualToString:@"Activity Summary - OpenSSL \"HeartBleed\" Scanning"] && [feed[@"UpdateTimestampGMT"] isEqualToString:threeDaysAgo]) {
//            minusThreeDayopenSSLCount++;
//        }

到

if ([feed[@"Classification"] isEqualToString:@"Activity Summary - OpenSSL \"HeartBleed\" Scanning"] && [feed[@"UpdateTimestampGMT"] isEqualToDate:[NSDate date]]) {
            openSSLCount++;
        }

它给了我这个错误：

2015-11-05 17：38：08.138 FYP_IOS_APP [938：448845] - [__ NSCFString isEqualToDate：]：无法识别的选择器发送到实例0x15cd90340 2015-11-05 17：38：08.139 IOS_APP [938：448845] ***由于未捕获的异常'NSInvalidArgumentException'终止应用程序，原因：' - [__ NSCFString isEqualToDate：]：无法识别的选择器发送到实例0x15cd90340'

Answer 1

你可以这样做：

NSDate *now = [NSDate date];
NSDate *threeDaysAgo = [now dateByAddingTimeInterval:-3*24*60*60];

NSDateFormatter *df = [NSDateFormatter new];
df.dateFormat = @"yyyy-MM-dd'T'HH:mm:ss.SSS";

NSString *threeDaysAgoAsAString = [df stringFromDate:threeDaysAgo];

for (NSDictionary *feed in feeds) {
  if ([feed[@"Classification"] isEqualToString:@"Activity Summary - OpenSSL \"HeartBleed\" Scanning"] && [feed[@"UpdateTimestampGMT"] isEqualToString:threeDaysAgoAsAString]) {
    minusThreeDayopenSSLCount ++;
  }
}

总体而言，我认为你不应该比较字符串来检查日期的相等性，因为这意味着两个日期值必须完全相同（例如＆＃34; 2015-11-03T01：00：59。 503 ＆＃34;！=＆＃34; 2015-11-03T01：00：59。 502 ＆＃34;）...

的更新

试试这个：

NSCalendar *calendar = [NSCalendar currentCalendar];

NSDateComponents *components = [NSDateComponents new];
components.day = -3; // days to subtract

NSDate *now = [NSDate date];
NSDate *threeDaysAgo = [calendar dateByAddingComponents:components toDate:now options:0];

NSUInteger threeDaysAgoComparisonValue = [calendar ordinalityOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitEra forDate:threeDaysAgo];

NSDateFormatter *df = [NSDateFormatter new];
df.dateFormat = @"yyyy-MM-dd'T'HH:mm:ss.SSS";

for (NSDictionary *feed in feeds) {
  if ([feed[@"Classification"] isEqualToString:@"Activity Summary - OpenSSL \"HeartBleed\" Scanning"]) {
    NSDate *updateTimestampGMT = [df dateFromString:feed[@"UpdateTimestampGMT"]];
    NSUInteger dateComparisonValue = [calendar ordinalityOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitEra forDate:updateTimestampGMT];
    if (dateComparisonValue == threeDaysAgoComparisonValue) {
      minusThreeDayopenSSLCount++;
    }
  }
}

另一个更新

如果你的目标是＆gt; = iOS 8，你可以让threeDaysAgo日期变得更简单：

NSDate *threeDaysAgo = [[NSCalendar currentCalendar] dateByAddingUnit:NSCalendarUnitDay value:-3 toDate:[NSDate date] options:0];

HOPEFULLY FINAL EDIT：）

NSCalendar *calender = [NSCalendar currentCalendar];
NSDate *threeDaysAgo = [calender dateByAddingUnit:NSCalendarUnitDay value:-3 toDate:[NSDate date] options:0];

NSDateFormatter *df = [NSDateFormatter new]; // to create the dates in the for loop
df.dateFormat = @"yyyy-MM-dd'T'HH:mm:ss.SSS";

for (NSDictionary *feed in feeds) {
  if ([feed[@"Classification"] isEqualToString:@"Activity Summary - OpenSSL \"HeartBleed\" Scanning"]) {
    NSDate *updateTimestampGMT = [df dateFromString:feed[@"UpdateTimestampGMT"]];
    if ([calender isDate:updateTimestampGMT inSameDayAsDate:threeDaysAgo]) {
      minusThreeDayopenSSLCount++;
    }
  }
}