NSArray *timeArray = [device_data sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        
        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        
        [dateFormatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
        
         NSDate *date1= [dateFormatter dateFromString:obj1[@"time"]?:@""];
         NSDate *date2= [dateFormatter dateFromString:obj2[@"time"]?:@""];
        
        if (date1 == [date1 earlierDate: date2]) { 
            //降序
            return NSOrderedDescending;
            
        }else if (date1 == [date1 laterDate: date2]) {
            //升序
            return NSOrderedAscending;
            
        }else{
            return NSOrderedSame;
        }
        
    }];