How to instantiate a prefab assigned from the inspector in Unity?

šŸŒµ Needle Engine
1

I just want to instantiate a prefab that is assigned from the inspector in Unity. Here is my code

import {AssetReference, Behaviour, GameObject, serializable, InstantiateOptions} from "@needle-tools/engine";
import {Object3D} from "three";


export class BallSpawner extends Behaviour {
    
    // @serializable(GameObject)
    // ball: GameObject | null = null;  

    @serializable(AssetReference)
    ball? : GameObject;

    @serializable(Object3D) 
    spawnPoint: Object3D | null = null;

    timer: number = 0;



    public start(): void {
        console.log("BallSpawner started");
        console.log("BallSpawner ball: " + this.ball);
        console.log("BallSpawner spawnPoint: " + this.spawnPoint);
    }

    public update(): void {
        //instantiate the ball every 1 second
        this.timer += this.context.time.deltaTime;
        

        if (this.ball && this.spawnPoint && this.timer > 1) {
            console.log("BallSpawner update");
            GameObject.instantiate(this.ball) as GameObject;
            const spawnPoint = this.spawnPoint;
            
            //newBall.position.copy(spawnPoint.position);
            this.timer = 0;
        }
    }
}```

When I try ```ts
    @serializable(GameObject)
    ball: GameObject | null = null;   ```
I get the error:  ```Detected wrong usage of @serializable with Object3D or GameObject. Instead you should use AssetReference here! Please see the console for details.```

and when I try ```ts
    @serializable(AssetReference)
    ball? : GameObject;```

i get the error:
```instance.clone is not a function```

[Original Post on Discord](https://discord.com/channels/717429793926283276/1154747892867809360)

*by user 216692838757433347*
2

Hey :wave: AssetReference works similar to Addresables in Unity, in a sense that you need a special way how to laod and instatiate the object since it is not loaded yet.

There is a super simple API for that:
this.ball?.instantiate()

Mind that it is asynchronous and that it returns a callback when it loads and spawns, you can also await that call.

3

Full example: https://engine.needle.tools/docs/scripting-examples.html#reference-and-load-an-asset-from-unity-prefab-or-sceneasset

4

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You can always search the docs for a specific keyword :+1: :cactus:
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5

Regarding the code please note this difference - AssetReference and GameObject are separate things, the type in @serializable and on the property should match.

    // for prefab references - will be loaded dynamically with instantiate()
    @serializable(AssetReference)
    ball? : AssetReference;

    // for scene references - loaded at start already
    @serializable(GameObject)
    ball? : GameObject;
6

Thank you for the quick responses! Iā€™ll look through the questions and documentation to figure how to get the instantiated object to interact with the physics system

by user 216692838757433347

7

It should just do! No changes needed if that object has collider/rigidbody