Using AddComponent to add a Sub Class using a String

Question

I'm trying to temporarily add a component that is a sub class in order to load certain variables.

 var equipTex = GetEquipment("Gloves");

Gloves inherits from a type "Equipment".

 public string GetEquipment(string equipmentName)
     {
         var equipName = (Equipment)gameObject.AddComponent(equipmentName);
         Debug.Log(equipName);
 }

When I try the code above, I will get this:

Can't add component because class 'Gloves' doesn't exist! UnityEngine.GameObject:AddComponent(String)

However, if I were to assign "equipmentName" to Equipment, it will not give me that error.

I'm beginning to believe that subclasses cannot be used by storing their name as a string, and calling them by that string, but classes that inherit from Monobehaviour can.

Is their something that I'm not getting? Or will I have to try another method?

Answer 1

OK here I got it working with a generic type:

 void GetEquipment() where T : class, new(){
     gameObject.AddComponent(typeof(T));
 }

and you call like this:

     GetEquipment<Gloves>();

It works for me, so there is no reason it should not work for you. :)

Edit: Let's take an example. One file:

 using UnityEngine;
 using System.Collections;
 
 public class Equipment : MonoBehaviour {
 
     public Vector3 velocity;    
     public Transform _transform;    
     protected int health;
 
     public virtual void Start(){
         velocity = new Vector3(Random.Range(0.5f,1.5f),0,0);
         _transform = GetComponent<Transform>();
     }
     public virtual void Update(){
          //Some Update
     }
 }
 
 public class Gloves : Equipment {
     public int variable;
     public override void Start () {
         base.Start();
         variable =10;
     }
     
     public override void Update () {
         base.Update ();
     }
 }

Ok so we have in the same file two classes Equipment and Gloves that inherits from Equipment

Just for the example here is a third independent class:

 using UnityEngine;
 using System.Collections;
 
 public class NPC : Enemy {
     public int varToShowInTheInpsector;
     public override void Start(){
         base.Start ();
         varToShowInTheInpsector = 100;
     }
 
     public override void Update(){
                //Some stuff happening here
     }
 }

Now we have an object with another script that is not any of those above:

 using UnityEngine;
 using System.Collections;

 public class MyClass : MainClass {

     public override void Start () {
         base.Start ();
      }
 
     public override void Update () {
        //Many stuff here
       if(Input.GetKeyDown(KeyCode.A)) 
          GetEquipment<Gloves>();
       else if(Input.GetKeyDown(KeyCode.B)) 
          GetEquipment<NPC>();
       else if(Input.GetKeyDown(KeyCode.C)) 
          GetEquipment<Equipment>();
     }
     void GetEquipment() where T : class, new(){
         gameObject.AddComponent(typeof(T));
     }
 }

Try that on and you will see new script popping up on your inspector. I added some public variable so that you can see that the appropriate class is created. You see how easy it gets to add any custom component?

Answer 2

Answer by Seth-Bergman · Nov 16, 2012 at 09:16 AM

Your problem is, this is half C#, half JavaScript!!! Otherwise though, what you are trying to do will work perfectly, if you just get the SYNTAX right:

case JavaScript:

 function GetEquipment(equipmentName : String)
     {
        var equipName = (Equipment)gameObject.AddComponent(equipmentName);
        Debug.Log(equipName);
        return equipName.ToString();  //????
 }

...

 var equipTex = GetEquipment("Gloves");

in JAVASCRIPT, the class and subclass are declared this way:

[http://answers.unity3d.com/questions/7614/does-unity-support-inheritance-and-subclassing.html][1]

case C#:

 public string GetEquipment(string equipmentName)
     {
        Equipment equipName = (Equipment)gameObject.AddComponent(equipmentName);
        Debug.Log(equipName);
        return (string)equipName;   // ???
 }

....

 string equipTex = GetEquipment("Gloves");

the classes here are declared this way:

 public class Equipment : MonoBehaviour
 {

...etc

 public class Gloves : Equipment
 {

...etc [1]: http://answers.unity3d.com/questions/7614/does-unity-support-inheritance-and-subclassing.html

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fafase · Nov 16, 2012 at 09:19 AM 4

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If you refer to var being UnityScript, var is also a c# keyword http://msdn.microsoft.com/en-us/library/bb383973.aspx

FakeBerenger · Nov 16, 2012 at 09:20 AM 2

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Well, actually, you can declare a variable as 'var' in C# too. So his code is correct in C#.

SrBilyon · Nov 16, 2012 at 09:20 AM 0

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I was about to note that. I tried the same thing as above, but strangely, I'm getting the same error.

Seth-Bergman · Nov 16, 2012 at 09:33 AM 0

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OOps, my mistake... thought you were declaring the classes wrong, didn't know about that with var too.. :)

at any rate

the reason your script isn't working, incedentally, is that you need to save each class in a SEPARATE script

the name of the file is the reference to the contained class

fafase · Nov 16, 2012 at 09:39 AM 0

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I got it working with both classes in the same file. This is just a matter of making the function generic and telling the compiler you want the type to be a class and have the new constraint.

Fact is there might be some less scary ways but they would be longer to write and debug :).

Answer 3

Answer by FakeBerenger · Nov 16, 2012 at 09:26 AM

I tested it, and your problem is that Gloves is in the same file as Equipment. Create a Gloves.cs. It would have worked with AddComponent( typeof(Gloves) ) though.

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SrBilyon · Nov 16, 2012 at 09:31 AM 0

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I had a feeling that was the reason. I was trying to be lazy and call the equipment by name, though, the problem with the second part of your solution, combined with my "lazy idea" is that i wouldn't be able to use (typeof(equipmentName)), since the contents of "equipmentName" would be the type.

I'm mainly using the string technique so that I won't have to write 20+ .CS files for like, 5 lines of code in each .CS.

FakeBerenger · Nov 16, 2012 at 09:33 AM 1

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Lazy ideas have a tendancy to backfire :p

SrBilyon · Nov 16, 2012 at 09:35 AM 0

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Yeah, they have a tendency of wasting a lot of time when they don't work :D

Seth-Bergman · Nov 16, 2012 at 10:37 AM 1

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So, ultimately though, your original suspicion was correct, it seems:

using the STRING version rather than the generic was the problem.. :

(as originally stated ) ...subclasses cannot be used by storing their name as a string, and calling them by that string, but classes that inherit from Monobehaviour can.

Answer 4

Answer by SrBilyon · Nov 16, 2012 at 09:33 AM

For the moment, to get it in a working condition, I started writing functions for each Equipment, and I'm using

 SendMessage(equipmentName);

to call the function with the appropriate name of the Equipment I want. That function will load the values I need, and presto. Now that I think about it, writing a class for each equipment would have been a little overboard, since I only need the classes to hold variables XD

What are you guy's opinion on this?

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Using AddComponent to add a Sub Class using a String

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