我可能错过了一些小细节，但是想不出来。尝试创建一个日期进行比较，但是似乎无法将当前日期从格林威治标准时间偏移为东部标准时间（EST）：
// current date (gmt) //
NSDate *currentDate = [NSDate date];
NSTimeZone *currentDateTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"EST"];
NSDateFormatter *currentDateFormat = [[NSDateFormatter alloc]init];
[currentDateFormat setTimeZone:currentDateTimeZone];
[currentDateFormat setDateFormat:@"yyyy-MM-dd HH:mm:ss zzz"];
NSString *currentDateString = [currentDateFormat stringFromDate:currentDate];
NSLog(@"currentDateString: %@", currentDateString); // returns 2011-01-05 13:30:30 EST
NSDate *currentDateWithOffset = [currentDateFormat dateFromString:currentDateString];
NSLog(@"currentDateWithOffset: %@", currentDateWithOffset); // returns 2011-01-05 18:30:30 +0000
谢谢！
编辑：
我正在调用另一个类中的方法（试图使其可移植），使用以下代码行：
[Expiration expires:[[NSDate alloc] initWithString:@"2011-01-07 12:00:00 +0000"] within:1.0]
在expires方法中，我有以下几行代码：
NSComparisonResult comparison = [currentDateWithOffset compare:expires]; // check for a fixed date to disable the demo
double withinRange = [installDate timeIntervalSinceDate:currentDateWithOffset]; // check for number of seconds between "within" and the install date
然后我会像这样比较这两个值：
if(withinRange >= within && withinRange > 0.0) {
// app is expired //
}
else {
// app is still enabled (so far...) //
if(comparison == NSOrderedDescending || comparison == NSOrderedSame) {
// app is expired //
}
else {
// app is still enabled //
}
}
这对您有帮助吗？感谢您的耐心！
编辑：
以下是expires:within方法的完整代码...
+(BOOL)expire:(NSDate*)expires within:(double)within {
// default expired value //
BOOL expired = NO;
// convert within value from days to seconds //
within *= 24.0 * 60.0 * 60.0;
// current date (gmt) //
NSDate *currentDate = [NSDate date];
// install date //
NSDate *installDate = [[NSUserDefaults standardUserDefaults]objectForKey:@"installDate"];
// check for a value in installDate //
if (nil == installDate) {
// app is running for the first time //
[[NSUserDefaults standardUserDefaults]setObject:currentDate forKey:@"installDate"];
[[NSUserDefaults standardUserDefaults]synchronize];
installDate = currentDate;
}
if([installDate timeIntervalSinceNow] < (-within)) {
expired = YES;
}
else {
if([expires timeIntervalSinceNow] < 0) {
expired = YES;
}
}
NSLog(@"installDate:%@", installDate);
NSLog(@"expires:%@", expires);
NSLog(@"currentDate:%@", currentDate);
return expired;
}
我现在需要从另一个类中调用它：
message.text = (YES == [Expiration expire:[[NSDate alloc] initWithString:@"2011-01-07 12:00:00 -0500"] within:(0.015625/2)]) ? @"This App is Expired" : @"This App is Active";
在模拟器中（新应用程序安装时），NSLog 显示了以下内容...
[Session started at 2011-01-06 10:43:46 -0500.]
2011-01-06 10:43:48.146 TimeBasedDemo[14717:207] installDate:2011-01-06 15:43:48 +0000
2011-01-06 10:43:48.147 TimeBasedDemo[14717:207] expires:2011-01-07 17:00:00 +0000
2011-01-06 10:43:48.147 TimeBasedDemo[14717:207] currentDate:2011-01-06 15:43:48 +0000
10:43:48 -0500而不是15:43:48 +0000。事实上，这没关系。它们是同一个时间。这只是在调用 NSLog 时的打印格式而已。 - Nick Moore