How do I access prefabs in the code in c#?

Question

I am currently making a Terraria like game. What I want is when I hold the mouse button down on a grass block, I want it to load a breaking animation and when the animation is complete, the block will be destroyed and added to the players' inventory. Because the terrain is randomly generated, I do not have a gameobject in the hierarchy to represent each block, this would be stupid to have. I simply have a single GrassBlock prefab in the Assets folder and use a for loop to generate the terrain. Now here comes the problem, I do not know how to access the GrassBlock prefab in the code and therefore when I run the game and hold the mouse button on a GrassBlock(Clone) there is not breaking animation. Only if I drag the prefab into the hierarchy and run the game, and then hold the mouse button will there be a breaking animation. Instead of accessing the prefab, I thought to access the GrassBlock(Clone) when the game is run:

     Animator blockAnim;
     GameObject x;
    
     // Use this for initialization
     void Start () {
         currentHealth = maxHealth;
         rb2D = GetComponent<Rigidbody2D>();
         anim = GetComponent<Animator>();
         FirePos = transform.Find("FirePosition");
 
         //this is how I would access the GrassBlock(Clone) GameObject
         x = GameObject.Find("GrassBlock(Clone)");
         blockAnim = x.GetComponent<Animator>();
     }

This however gives me this error - NullReferenceException: Object reference not set to an instance of an object. Error is on the follwing lines:

 void Start () {
         currentHealth = maxHealth;
         rb2D = GetComponent<Rigidbody2D>();
         anim = GetComponent<Animator>();
         FirePos = transform.Find("FirePosition");
 
         //this is how I would access the GrassBlock(Clone) GameObject
         x = GameObject.Find("GrassBlock(Clone)");
         blockAnim = x.GetComponent<Animator>(); // I get the error here
     }

This method is used to check weather the mouse button has been pressed on an a block

 public void __BreakBlock__(string blockTagName, GameObject blockToAdd)
     {
         if (AddToInventory)
         {
             Inventory.Add(blockToAdd);
 
         }
         Vector2 mouse_position = Camera.main.ScreenToWorldPoint(Input.mousePosition);
 
         mouse_position = new Vector2(Mathf.Round(mouse_position.x), Mathf.Round(mouse_position.y));
 
         RaycastHit2D hit = Physics2D.Raycast(Camera.main.ScreenToWorldPoint(Input.mousePosition), Vector3.forward);
 
         if (Input.GetMouseButton(0))
         {
 
             if (hit)
             {
 
                 if (hit.collider.tag == blockTagName && hit.collider.tag != "player")
                 {
                     blockAnim.SetInteger("State", 1); //I get the error here
 
                 }
             }
         }
         else
         {
           
             blockAnim.SetInteger("State", 0); //I get the error here
             AddToInventory = false;
         }

This is not my entire script as it is more than 300 lines. These are just the lines that are responsible for my issue. If you want to see the entire script, I will provide it.

Answer 1

Answer by Larry-Dietz · Dec 31, 2017 at 05:40 PM

Your GameObject.find will return the first instance of a block named "GrassBlock(Clone)" Not necessarily the one you are clicking on. and then only if that name matches exactly.

Your best bet to get a reference to the object when clicking on it, would be to do a raycast when you click, and use the hit return parameter to get the object. Once you have the object, you can assign it to a variable, x in your script above, and then get the Animator component from it.

I would recommend using the raycast you are already doing, and just assign the variable, and get the animator there. In your else for the hit, just remove the animation state set. Presumably the object is already in the "I haven't been clicked on" state. And since once clicked, you will play the animation and destroy the object, there would be no reason to reset the state later.

Hope this helps, -Larry

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user_invalid · Jan 01, 2018 at 02:31 PM 0

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@Larry-Dietz I tried applying what you said and it worked, well at least what I understood from what you said. I am not sure if the following code is what you meant -

 void __BreakBlock__(string blockTagName, GameObject blockToAdd)
     {
 
         //x = GameObject.Find(blockTagName+"(Clone)");
 
         if (AddToInventory)
         {
             Inventory.Add(blockToAdd);
 
         }
         if (loadBreakAnimation)
         {
             blockAnim.SetInteger("State", 1);
 
         }
         Vector2 mouse_position = Camera.main.ScreenToWorldPoint(Input.mousePosition);
 
         mouse_position = new Vector2($$anonymous$$athf.Round(mouse_position.x), $$anonymous$$athf.Round(mouse_position.y));
 
         RaycastHit2D hit = Physics2D.Raycast(Camera.main.ScreenToWorldPoint(Input.mousePosition), Vector3.forward);
 
         if (Input.Get$$anonymous$$ouseButtonDown(0))
         {
 
             if (hit)
             {
 
                 if (hit.collider.tag == blockTagName && hit.collider.tag != "player")
                 {
                     x = hit.collider.gameObject;
                     blockAnim = x.GetComponent<Animator>();
                     loadBreakAnimation = true;
                    
                 }
             }
         }
         else
         {
             loadBreakAnimation = false;
             AddToInventory = false;
         }
     
 
 
     }

The only small problem I am having now is when I hold the mouse button down on a block the animation plays, which is fine, but when I release the mouse button, the 'loadBreakAnimation' does not return false and continuously returns true, thus the animation keeps on playing. Do you have any idea why this might be? Either way, I still appreciate the help.

Larry-Dietz user_invalid · Jan 01, 2018 at 04:48 PM 0

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Ok, I was working on the assumption that the animation was occurring on the block that was being destroyed, so the animation would be destroyed along with the block.

Add this to your else clause. It will set your animation state, ONLY if an animator was previously found.

     if(blockAnim!=null)
         blockAnim.SetInteger("State", 0);

That should set the integer for state, if the animator is known, and not throw a null reference if it is not known.

Hope this helps,

user_invalid Larry-Dietz · Jan 01, 2018 at 05:15 PM 0

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Thank you, this worked. I really appreciate the help. Just one thing, if you can, do you by any chance know how to check if an animation has finished? As I want the block to be destroyed after the animation has finished.

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How do I access prefabs in the code in c#?

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