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如果app在后台待机太久，再次进来前台的时候也应该展示广告，所以在applicationDidEnterBackground的时候应该把时间存起来：
//程序切入后台,这里要注意GMT时间 NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"]; [formatter setTimeZone:sourceTimeZone]; [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; _lastTimeEnterBackGroundStr = [formatter stringFromDate:[NSDate date]];//当前时间
在applicationWillEnterForeground的时候对比时间差，判断是否显示:
NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"]; [formatter setTimeZone:sourceTimeZone]; [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; NSDate * lastDate = [formatter dateFromString:_lastTimeEnterBackGroundStr]; NSDate * now = [formatter dateFromString:[formatter stringFromDate:[NSDate date]]]; NSTimeInterval IntervalTime = [now timeIntervalSince1970]*1 - [lastDate timeIntervalSince1970]*1; if (IntervalTime>(2*60*60)) { [_mainController loadAdvertisedView]; }
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原文地址：http://www.cnblogs.com/HJQ2016/p/5814771.html
