Introduction – What is this error?
In this article we look at the causes of the “Can’t Add Script” error in Unity in order to understand why it occurs and identify what actions to take to fix it.
For the absolute begginers, let’s suppose you create a new script in Unity and you name it “MyUnityScript“, when you open that script you are going to notice that there are already some text inside (for example the Start and Update functions), when new scripts are created Unity also creates a programming class with the same name that you use on the script file, in our case at the top of the script we see something like this:
public class MyUnityScript : MonoBehaviour {
So we created a script (which is a text file) called “MyUnityScript ” and Unity automatically created a class called “MyUnityScript“, that is the “class” that the error message is telling us about, Unity for some reason is not able to find it.
In most cases this error occurs because there were console errors in Unity at the time of creating the script, so Unity did not compile and did not add the script to its registry.
Unity won’t compile until you solve all the errors in the console.
There is a video tutorial on this topic:
Why do the “Can’t Add Script” Error occur in Unity?
This error in which we are not allowed to add a Script or component to a GameObject can arise for two reasons.
Case 1: The name of the script and the name of the class it defines do not match
The first one is that the name of the Script, that is to say, the name of the file with extension “.cs” does not match the name of the programming class that is defined inside it. This usually happens when we create a Script and then change the name of the file without doing a Refactoring process.
To solve this problem first we must identify the Script that has conflicts, this can be done with the information provided by the “Can’t Add Script” error window that appears when we try to add the Script with conflicts to a GameObject. If you do not remember which Script produced the error, you can create an Empty GameObject and start adding each of the Scripts until the error appears.
Once we know which is the Script that generates the “Can’t Add Script” error, we open it and we locate the part of the class definition, which begins as follows:
public class NameOfTheClass …
The name of the class is the name that has to match the name of the file, so what you can do is modify the name of the class to match the name of the file, or modify the name of the file to match the name of the class.
Once this problem is solved it will be possible to add the Script to a GameObject. If you need to rename the Script the best way is to right click on the “NameOfTheClass” name and then click on “Rename”, this will make Unity modify that name in all the places where that Script is used.
Case 2: The script was created having errors in the console
We already address this cause in the introduction because I consider is the most common case, but let’s repeat, the second reason why the “Can’t Add Script” error occurs in Unity is when new Scripts are created while there are errors in console, in general these are syntax errors (errors in writing the code). The reason in this case is that if there are errors in console, Unity cannot compile, therefore if we create a new Script at this point, even if the file has been created, the programming class cannot be added to the engine, in other words Unity will not know that this Script exists until it compiles.
The solution in this case is to solve all the errors in the console, this will make Unity compile and register the new Script. Once that issue is solved you should be able to assign the Script to a GameObject.
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