ios日期比较

 1 +(int)compareDate:(NSDate *)date1 date:(NSDate *)date2
 2 {
 3     NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
 4     [dateFormatter setDateFormat:@"yyyy-MM-dd"];
 5      //比较准确度为“日”，如果提高比较准确度，可以在此修改时间格式
 6     NSString *stringDate1 = [dateFormatter stringFromDate:date1];
 7     NSString *stringDate2 = [dateFormatter stringFromDate:date2];
 8     NSDate *dateA = [dateFormatter dateFromString:stringDate1];
 9     NSDate *dateB = [dateFormatter dateFromString:stringDate2];
10     NSComparisonResult result = [dateA compare:dateB];
11     if (result == NSOrderedDescending) {
12         return 1;  //date1 比 date2 晚
13     } else if (result == NSOrderedAscending){
14         return -1; //date1 比 date2 早
15     }
16     return 0; //在当前准确度下，两个时间一致
17 }