iphone之NSArray比较大小

 //排序
                    NSArray *tempArray = [[NSArray alloc]initWithArray:self.contentArray];

                    tempArray = [tempArray sortedArrayUsingComparator:^NSComparisonResult(NewCenter *newCenter1, NewCenter *newCenter2) {

                        NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
                        [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];

                        NSDate *date1 = [formatter dateFromString:newCenter1.newtime];
                        NSDate *date2 = [formatter dateFromString:newCenter2.newtime];

                        int i = [date1 compare:date2];

                        return -i;
                    }];

NewCenter是自定义的类