Instantiating problems

Question

I'm beginner here, I'm trying to instantiate a single object every specific duration, either form the left of the screen or from the the right, at the same time I want this object to move to the other side of the screen

So the troubles I'm facing here are:

1. sometimes 2 objects are being instantiated at the same time.
2. the objects move in the direction that are defined in the first if statement (both objects on the left and the right move in one direction)

the part where I instantiate objects is in the script(smallFishes) that's attached to an empty gameobject is :

void Start () {
    timer = gameObject.AddComponent<Timer>();
    width = 2f;
    timer.Duration = 3;
    timer.Run();
    left = Resources.Load("Left") as GameObject;
    right = Resources.Load("Right") as GameObject;

}
void Update () {

    if (timer.Finished)
    {
        lr = Random.Range(1, 3);
        if (lr == 1)
        {
            var generetx = -8.8f - width / 2;
            Instantiate(left, new Vector2(generetx, Random.Range(-4.8f,4.8f)), Quaternion.identity);
        }
        else
        {
            var generetx = +8.8f + width / 2;
            Instantiate(right, new Vector2(generetx, Random.Range(-4.8f, 4.8f)), Quaternion.identity);
        }
        timer.Duration = 3;
        timer.Run();
    }

}
public int state
{
    get { return lr; }
}

the part where I make the object move from the script that's attached to the object prefab:

void Start () {
    small = gameObject.AddComponent<smallFishes>();
    rb2d = gameObject.GetComponent<Rigidbody2D>();
}

void Update()
{
    var fishes = GameObject.FindGameObjectsWithTag("small");
    if (fishes!=null)
    {
        if (small.state == 1)
        {
            moveright = new Vector2(4 * Time.deltaTime, 0);
            rb2d.AddForce(moveright, ForceMode2D.Impulse);
        }
        else
        {
            moveleft = new Vector2(-4 * Time.deltaTime, 0);
            rb2d.AddForce(moveleft, ForceMode2D.Impulse);
        }
    }
}

Thanks in advance.

Answer 1

It's quite likely that if (timer.Finished) is satisfied twice. As Update is called once for each frame it seams that timer.Finished is true for two frames in a raw.

Possible solutions:
Falsifying timer.Finished as soon as it's true value is consumed can be a solution.
Or detecting change of timer.Finished from false to true and executing code on that event also can be a solution.

Or just detecting the change not only true value:

bool timerFinishedPrevious = false;
void Update () {

    var timerFinishedToTrue = timerFinishedPrevious == false && (timerFinishedPrevious != timer.Finished);

    if (timerFinishedToTrue)
    {
        lr = Random.Range(1, 3);
        if (lr == 1)
        {
            var generetx = -8.8f - width / 2;
            Instantiate(left, new Vector2(generetx, Random.Range(-4.8f,4.8f)), Quaternion.identity);
        }
        else
        {
            var generetx = +8.8f + width / 2;
            Instantiate(right, new Vector2(generetx, Random.Range(-4.8f, 4.8f)), Quaternion.identity);
        }
        timer.Duration = 3;
        timer.Run();
    }

    timerFinishedPrevious = timer.Finished;
}