- (void)applicationDidEnterBackground:(UIApplication *)application
{
    NSString *path = [self filePath:@"test.txt"];
    if ([[NSFileManager defaultManager] fileExistsAtPath:path])
    {
        NSLog(@"file exist");
    }
    else
    {
        NSLog(@"create file");
        MyObject *myObj = [[MyObject alloc] init];
        myObj.name = @"peter";
        myObj.age = 18;
        myObj.color = @"blue";
    NSMutableData *data = [[NSMutableData alloc] init];
        NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
        [archiver encodeObject:myObj forKey:@"MY_OBJ"];
        [archiver finishEncoding];
        [data writeToFile:path atomically:YES];
    }
}