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How to randomize what scriptable object gets loaded

I am a complete noob when it comes to coding in unity . I have a couple of different enemies that are scriptable objects and when I start a battle I would like to load a random one of those enemies. Can anyone please help I cant figure out how to do it.

It depends on what you have. Are you loading Scriptable Objects from the Resources folder? If you are, you may use Object[] enemies = Resources.LoadAll("Enemies", typeof(Enemy)). This code will load everything of a type "Enemy" from a folder "Resources/Enemies/". Then you can get random numbers from 0 to enemies.Length and get an object from the array using the number as an index

Spawning gameobjects relative to the position, width and length of another gameobject?

I'm currently developing a game in Unity using C# and I've run into a small problem.
I need to spawn a certain gameobjects relative to the Spawnposition and length of another game object. Now I figured that bounds.size would be the best function to use in this instance. As shown bellow I declare first the variable that uses this in my start method:
public void Start()
{
GameObject PointBar = (GameObject) Resources.Load("PointBar Horizontal");
PointBarVectorLength = PointBar.GetComponent<BoxCollider2D>().bounds.size.x;
PointBarVectorConv = Camera.main.WorldToViewportPoint(new Vector2(PointBarVectorLength, 0f));
}
However, the gameobjects in question are inactive at start's call and thus I presume don't return any value for bounds.size when called.
Does anyone know how I can access the bounds.size or equivalent of an inactive gameobject or is there something else I'm missing here?

As noted in the documentation for the Collider.bounds property, bounds "will be an empty bounding box if the collider is disabled or the game object is inactive". So your assumption was pretty much right. Since the object doesn't exist in worldspace that makes sense.
I'm not sure about the most elegant solution for your use case but two options spring to mind.
Calculate the object's spawn dimensions by accessing its transform.localScale and factoring in the scale of prospective parent objects. That could get messy but you could probably also write a helper method to make it more manageable.
Instantiate the object somewhere off screen after you load it, access its Collider.bounds property to get the information you need then move it where ever you want it or store the information for later.
There may be better solutions but that's what leaps to mind for me.

I solved the issue by using GetComponent().bounds.size.x;
instead of BoxCollider. This component can get accessed when the game object is not active.

How to have an object in Unity 3D that stays in scenes and does not recreate

I’m trying to find a good way to play background music in Unity 3D. I want the music to keep playing consistently through scene loads. Don’t Destroy on load is fine and works, but every time I load the same scene, it makes another music game object because the scene itself has the game object in it. How can I solve my problem? I am a “beginner” (kind of), so I would like code I can understand.

I'd hands down recommend starting with an Asset like 'EazySoundManagerDemo'. It needs a little refactoring and refinement (ie it uses 3 arrays of audios with 3 sets of accessibility functions instead of one set with an AudioPurpose enum to increase code-reuse).
It does however solve the basic problem you have and is a good intro to using an audio manager / layer instead of simply playing audio directly from your GameObjects. Give that a shot, learn from it and then adapt it or create your own audio management layer.
Good Luck!

I recommend creating an audioSource object, then creating an script for this object and on the awake function do this:
void Awake() {
DontDestroyOnLoad(this.gameObject);
}
This will make the background music to keep playing between scenes. For more information you could use Unity's documentation about this function.

With help from a question on the unity forum, I think I have solved my problem. The link to the question is here...
https://answers.unity.com/questions/982403/how-to-not-duplicate-game-objects-on-dontdestroyon.html
The Best Answer is the one I’m using.
The code is this...
private static Player playerInstance;
void Awake(){
DontDestroyOnLoad(this);
if (playerInstance == null) {
playerInstance = this;
} else {
Destroy(gameObject); // Used Destroy instead of DestroyObject
}
}

Infinite Road Update

I am working on Unity for a month. I am new on Unity and C#, before Unity I worked other game engines. Whatever I am working on infinite run game, I wrote random road generator. Road generator is working well but I have problem about updating road. I can update road manualy like this. How can I update it automaticly?
void Update()
{
if(Input.GetKeyDown(KeyCode.A)) UpdateRoad();
}
My UpdateRoad method adding road like this(I am using object pooling).
I want to update after Link Road, OnExitTrigger or something I dont know. How can I do it?

You would need to implement Object Pooling.
I would suggest making your Design of Objects first so you can test. Or if not use, the stock Blocks Primitive of Unity3D as your Prefabs. I hope you already know prefabs. It is a major key for making infinite runner. Actually a main core for making any kinds of game.
Prefabs is an Object File where you can Instantiate it in a location. So lets say you will generate a Flat walkable, then Generate a Pit. You would probably want to stack them together.
Now Generating them is easy. You would not like to go in an Update? Approach because most likely you're not going to update, but you're going to further stack what is going on ahead, based on your game logic.
To further Understand this, Unity3D already made a project or Fully Detailed tutorial. It maybe made in 2D but it is going to be the same, if you're going to change the Collider2D to Collider <- this is important in your case.
https://unity3d.com/learn/tutorials/modules/beginner/live-training-archive/infinite-runner
Update
You would need to create an Object, that is invisible. Meaning a Trigger.
Then on Trigger call your method UpdateRoad();
https://unity3d.com/learn/tutorials/modules/beginner/physics/colliders-as-triggers
Detailed Videos about Trigger.

If I understood your needs correctly, you could create Empty Object name it SpawnPoint, set position for Spawn Point as you need (out of the camera view) and then Instanciate random prefabs of road. Concerning On TriggerExit - it could be used to destroy "old piece of road". But to have it working properly, dont forget to set collider and rigitbody to your objects. Dont add collider2D or Rigitbody2d, add and use Box Collider and Rigitbody components

find preveously spawned gameobject in unity

I am trying to make a simple 2d platformer endless running game using unity game engine also i am completely new to the unity game engine and c# scripting. Within the game i am using the instantiate for spawning the platforms. I managed to spawn gameobjects to the scene. My question is that how to find the previously spawned objects using c# script. it will be a great help if anyone provided the code. And sorry for my bad language

List<Object> existingOnes = new List<Object>();
var clone = Instantiate(...);
clone.name= "0001";
existingOnes.Add(clone);
var theOne = existingOnes.Where(item
=> item.name.Equals("0001").FirstOrDefault();
Note that "theOne" might no longer exist if you dynamically destroyed it.
If the clone is GameObject, you can also use:
GameObject.Find(...)
to get access to it.