assign variable unity

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Unity Visual Scripting Part 6: Variables

In this part, we’ll get to know Variables in Unity’s Visual Scripting. In short, variables are containers that store information and values.

A variable has a name, a type, and a value. The value inside a variable can change throughout the game. Imagine we have a cookie jar and an envelope. The cookie jar can contain different kinds of cookies, be it chocolate cookies or macaroons. An envelope, on the other hand, may only contain letters or postcards. Every container can contain any value as long as it shares the same data type. Therefore, we can’t put a cookie inside an envelope. At any point, we can check which cookie is stored in the jar or replace it with another cookie.

Each variable belongs to a single Scope. We may want a variable to only be accessible to the current script graph, all scripts in the scene, or even remember its value after quitting the game. In Unity’s Visual Scripting, there are five kinds of Scopes: Graph, Object, Scene, Application, and Saved.

Graph variables

Graph variables are local to the specific Script Graph. Therefore, they cannot be accessed or modified outside the script they are created in.

Object variables

Object variables are shared across all script graphs attached to a GameObject. Note that we can also edit Object variables in the GameObject Inspector.

Scene variables

Scene variables are shared across all the script graphs in the current scene. We can also edit these scope variables in the Inspector of the ‘Scene Variables’ GameObject placed in the scene. This GameObject will be created by Unity.

Application variables

Application variables are accessible from any script graph; their values remain even when the scene changes. However, they will reset once we quit the game.

Saved variables

Saved variables will persist even after we quit and resume the game.

Why should we use a small scope when one could use a larger access scope, like the Application scope? There may be times when different objects will have similar variables, for example, health points. All enemies will have health points, but we need to differentiate each enemy’s health separately, according to the damaged they have taken. It can be confusing at first. But over time, it will become evident which scope to use.

Creating a Variable

To add a variable, we choose the relevant scope tab, name the variable, and press enter. We can now select the data type the variable will remember, then we will fill in an initial value.

Under the Saved scope tab, we have Initial and Saved sub-tabs. In the initial tab, we define the values that will automatically be created for new games. In the saved tab, we can see the state of saved variables for our current computer.

In the graph, we use the Get Variable node to get the information stored in it. This node gives us the current value stored in the variable. Searching it at the Fuzzy Finder will present us with different scopes to select from. We can also change the scope at the nodes themself. We get our variable by either typing its name or selecting it from the list. In this example, I have connected the Get Variable node to a Debug Log node, which will print the variable’s value to the console.

We can also change a variable’s value at any time by using the Set Variable node. In this example, I have created a Scene variable that remembers a boolean data type and set it to false.

Next up, we’ll discuss working with loops & collections.

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Assigning components to variables in Unity, benefits?

I'm wondering if it's beneficial to assign components to variables in Unity C#, as follows

Whereas the shorter version would be without initialising the object as a variable, besides readability are there benefits to using one way or the other?

• 1 \$\begingroup\$ When would you rather pay the cost of searching for this object? At start-up or on scene load? Or would you prefer to avoid the search cost entirely? \$\endgroup\$ –  DMGregory ♦ Apr 10, 2020 at 18:40
• \$\begingroup\$ How could I avoid the search cost entirely? As I see it now I only see the start-up or scene load option \$\endgroup\$ –  Miguel Stevens Apr 10, 2020 at 18:46
• \$\begingroup\$ Expose your variable publicly, or private but serialized, so you can assign the reference in your inspector at edit time. No searching at runtime then. \$\endgroup\$ –  DMGregory ♦ Apr 10, 2020 at 18:47
• \$\begingroup\$ So everything you assign in SerializableField is calculated beforehand, thus increases performance? \$\endgroup\$ –  Miguel Stevens Apr 10, 2020 at 18:54

This use of member variables is called caching. It's a space-time trade-off: we use a little extra memory (space) to save ourselves the computation work (time) needed to produce the value from scratch every time.

For something like a reference variable, the memory cost is trivial, so this is a very efficient trade-off to make, if it helps you avoid repeatedly paying a computation cost, or shift that cost to a more convenient moment.

You'll often see it used in cases like this, where we have a homing projectile or enemy that wants to move toward the player every simulation step:

Here we're spending time in every physics step to search through all our game objects to find the player object - even though we just did that same search last physics step!

As the Unity docs say ,

It is a general best practice to eliminate all usage of Object.Find and Object.FindObjectOfType in production code. As these APIs require Unity to iterate over all GameObjects and Components in memory, they rapidly become non-performant as the scope of a project grows.

So for a case like this, it's recommended to limit your searching: say, do it just once and remember the result for subsequent frames:

Now we pay the search cost only once, rather than every physics step.

Or better yet, if we can read a reference to our target from a manager/singleton (global variable), or have it passed to us on initialization from a class that already knows our target via eg. a SetTarget(Transform target) method (dependency injection), we can avoid ever searching for it at all. :)

In your particular example, the search is occurring only once anyway. All that's different is whether you're doing that search when this script starts up (eg. when the scene it's in loads), or when it needs to do its work (when the next scene transition happens).

Often a lot of scripts will be doing their setup or searching for their dependencies in Start() , so deferring this search until later - so you don't need a Start() call on this object - might help you reduce the performance hitch you see when first loading a scene.

But in this case you might have an even better option. It looks like both the SceneLoader script and the GameStatus script exist in the same scene file. If that's the case, you can expose your gameStatus variable to be populated in the Inspector when you're authoring the scene:

Now just like before you don't need a Start() method, and you also don't need to search for this reference when it's time to use it. It's been pre-populated for you at edit time, and it's a quick copy operation for the deserializer to fill in the variable when your scene loads.

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• Scripting API
• unity3d.com

Unity Manual

• Unity User Manual (2019.3)
• Visual Scripting with Bolt
• Basic Concepts

Variables are containers. Each variable has a name, a type, and a value.

The value inside a variable can change during runtime, which is why they’re called vary-ables.

In Bolt, there are 6 kinds of variables:

The variables window

The variables window can be opened via Windows > Variables . It contains one tab per kind of variable. The graph tab is only enabled if a flow graph is selected, and the object tab is only enabled if a game object is selected.

Adding a variable

• Choose the tab corresponding to the kind of variable you want to add
• Type the name of the new variable in the New Variable Name field
• Click the plus button
• Choose its type
• (Optional) Change its default value

Saved and Initial Variables

You may notice that under the Saved tab, there are two sub-tabs: Initial and Saved.

In the initial tab, you define values that will automatically created for new games.

In the saved tab, you can see the state of saved variables for your current computer. You can edit these manually or delete them all if you want to start anew.

Removing Headers

Once you get a good grip of how each kind of variable works, you can remove the headers in the variables window to save some screen real-estate. Simply uncheck Show Variables Help in Tools > Bolt > Editor Preferences….

Dynamic Variables

Variables don’t need to be declared during edit mode! They can also be created during play mode.

Setting the value of a variable that doesn’t exist automatically creates it. For example, this graph would create a new saved integer variable named gold with a value of 250, even if we hadn’t defined it before:

Note that all object variables in Bolt are public and can be accessed by other objects.

Assigning variables to GameObjects

I am making a script to call variables from the object which hits the targets to calculate force. But, I was wondering if there was a simple way to make a private variable to that GameObject and later to be able to access it like you can do with transform.

In tranform you can do

terrain.transform or this.transform I want to be able to access a variable like that be able to do. var bulletWeight : float = GameObject.Find(“Bullet”).weight; bullet.mass etc.

Is there a way to do this? Without making a script to assign the value and then accessing that script value and calling it from there? I rather not do it this way unless I have too.

You cannot access private variables directly from other scripts at all. You would need getter/setter functions…

Public variables can be accessed by:

Also, GameObject.Find() should only ever be called in Start() or Awake(). Don’t call it repeatedly, since it is quite expensive.

You’ll have to do it via attached script classes (which can be attached as ‘components.’) Even the basic Gameobject is class that is a collection of other classes and structs (such as transform.)

Simple class example (c#)

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Can't assign a value to Transform variable

Discussion in ' Scripting ' started by dusthound , Jan 31, 2019 .

I am working on game and need to give a random value to the position of a transform component. I need to do this so that I have enemies spawning at random locations. So far, I have only gotten an error message saying that the object reference is not set to an instance of an object. How do I fix this? public class Spawner : MonoBehaviour { public GameObject enemy; public int enemies; public float e; private Transform st; private Transform t; private Vector2 v; public float maxenemies; public bool active; // Use this for initialization void Start () { enemies = 0; StartCoroutine(EnemyCreation()); } IEnumerator EnemyCreation() { while (active == true) { if (enemies < maxenemies) { yield return new WaitForSeconds(e); v = new Vector2(Random.Range(-5.0f, 5.0f), Random.Range(-5.0f, 5.0f)); t.position = new Vector2(v.x, v.y); st = t; Instantiate(enemy, st.position, st.rotation); enemies = enemies++; } } } // Update is called once per frame void Update () { } } [/code]  

Does t have a value? Also not the best variable name, but since it's private, not sure you assigned anything to it.  

Please use the "Insert Code" button when pasting your code so it's easier to read. You need to provide more information for the error you're getting and the line number it's on. My guess is that your "enemy" GameObject has not been assigned in the inspector so there's nothing to instantiate. I also spotted another problem in your EnemyCreation Coroutine, if the enemies counter ever exceeds maxenemies, your coroutine will not yeild so you'll be stuck in an infinite loop and your game will freeze. You need to put "yield return null;" just before you close your loop to prevent this from happening.  

Okay, I did use a code tag to insert my code. It must not have worked then. The enemy is a prefab object. Also, what does "yield return null" do, I would like to know how it works before putting it into my code.  

WarmedxMints

I think I see what you are trying to do. Try this; Code (CSharp):     public class Spawner : MonoBehaviour     {         public GameObject enemy ;         public int enemies ;         public float timeBetweenSpawn ;           private Vector2 spawnPos ;         private Quaternion spawnRot = Quaternion . identity ;           public int maxenemies ;         public bool active ;         // Use this for initialization         void Start ( )         {             enemies = 0 ;             StartCoroutine ( EnemyCreation ( ) ) ;         }           IEnumerator EnemyCreation ( )         {             var waitTime = new WaitForSeconds ( timeBetweenSpawn ) ;               while ( active == true )             {                 if ( enemies < maxenemies )                 {                     yield return waitTime ;                       spawnPos = new Vector2 ( Random . Range ( - 5 . 0f, 5 . 0f ) , Random . Range ( - 5 . 0f, 5 . 0f ) ) ;                       Instantiate ( enemy, spawnPos, spawnRot ) ;                       enemies ++;                 }             }         }     }  

Brathnann said: ↑ Does t have a value? Also not the best variable name, but since it's private, not sure you assigned anything to it. Click to expand...

WarmedxMints said: ↑ I think I see what you are trying to do. Try this; Code (CSharp):     public class Spawner : MonoBehaviour     {         public GameObject enemy ;         public int enemies ;         public float timeBetweenSpawn ;           private Vector2 spawnPos ;         private Quaternion spawnRot = Quaternion . identity ;           public int maxenemies ;         public bool active ;         // Use this for initialization         void Start ( )         {             enemies = 0 ;             StartCoroutine ( EnemyCreation ( ) ) ;         }           IEnumerator EnemyCreation ( )         {             var waitTime = new WaitForSeconds ( timeBetweenSpawn ) ;               while ( active == true )             {                 if ( enemies < maxenemies )                 {                     yield return waitTime ;                       spawnPos = new Vector2 ( Random . Range ( - 5 . 0f, 5 . 0f ) , Random . Range ( - 5 . 0f, 5 . 0f ) ) ;                       Instantiate ( enemy, spawnPos, spawnRot ) ;                       enemies ++;                 }             }         }     } Click to expand...

I mean assigning a value to the variable. You declared a variable, but it has no value.  

I did that in the code, the transform is given the value of a Vector2.  

A transform is not a vector2. t.position is a strut on the transform, so no, you did not assign a value to t, thus t is null.  

dusthound said: ↑ what does "yield return null" do Click to expand...

• v = new Vector2 ( Random . Range ( - 5 . 0f, 5 . 0f ) , Random . Range ( - 5 . 0f, 5 . 0f ) ) ;
• Instantiate ( enemy, v, Quaternion . identity ) ;

Brathnann said: ↑ A transform is not a vector2. t.position is a strut on the transform, so no, you did not assign a value to t, thus t is null. Click to expand...

Same way you do any other variable...assign a Transform to a transform variable... Code (CSharp): Transform t = targetGameobject . transform ; as an example...  

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Set functions as variables to call, Unity

So that I will be able to put an object, select the one of the scripts from it, and call a function from it. The logic whenever to call it will be handled in the script itself, something like if(callFunctions) { for(int i = 0; i < functionArray.length(); i++){ functionArray[i].call();}} I did try to review the button's script but couldn't recreate this functionality.

• unity-game-engine

• This can be done using reflection and a custom inspector. However, I'd advise against it. Reflection is slow and you probably do not want to use it unless you really have to. You could just use a UnityEvent if that's enough for you? –  Max Play Oct 23, 2022 at 15:27
• Yes, it seems that's the right place to start, but I still don't understand how to m_MyEvent.AddListener(function); with a function from another script, preferably without knowing what the other's script function's name is. –  Aliph Null Oct 23, 2022 at 16:14
• 1 If you define the variable as UnityEvent type you can assign methods to it as above –  BugFinder Oct 23, 2022 at 16:40

That can be done using UnityEvents. Take a look at this video

https://www.youtube.com/watch?v=TWxXD-UpvSg

• that was embarrassingly easy, thanks –  Aliph Null Oct 23, 2022 at 18:19

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