Scene loading and unloading in Unity - Step-by-Step Execution

Concept Flow - Scene loading and unloading

Start

↓

Call LoadScene

↓

Scene Loads

↓

Scene Active

↓

Call UnloadScene

↓

Scene Unloads

↓

Back to Start or Next Scene

This flow shows how a scene is loaded, becomes active, and then unloaded in Unity.

Execution Sample

Unity

using UnityEngine;
using UnityEngine.SceneManagement;

public class SceneLoader : MonoBehaviour
{
    public void LoadAndUnload()
    {
        SceneManager.LoadScene("Level1", LoadSceneMode.Additive);
        SceneManager.UnloadSceneAsync("Level1");
    }
}

This code loads a scene named 'Level1' and then unloads it asynchronously.

Execution Table

Step	Action	Scene State	Result
1	Call LoadScene("Level1")	Level1: Not Loaded	Starts loading Level1 scene
2	SceneManager loads Level1	Level1: Loading	Scene assets load into memory
3	Level1 scene becomes active	Level1: Loaded and Active	Scene is ready to use
4	Call UnloadSceneAsync("Level1")	Level1: Loaded and Active	Starts unloading Level1 scene
5	SceneManager unloads Level1	Level1: Unloading	Scene assets removed from memory
6	Level1 scene fully unloaded	Level1: Not Loaded	Scene no longer in memory

💡 Scene is fully unloaded, no longer active or in memory

Variable Tracker

Variable	Start	After LoadScene	After Scene Active	After UnloadSceneAsync	After Unload Complete
SceneState	Not Loaded	Loading	Loaded and Active	Unloading	Not Loaded

Key Moments - 3 Insights

Why does the scene state change from 'Loading' to 'Loaded and Active'?

Because after LoadScene is called, Unity loads all scene assets, then activates the scene making it ready to use (see execution_table steps 2 and 3).

What happens if you try to unload a scene that is not loaded?

Nothing happens because the scene is not in memory; unloading only works on loaded scenes (see execution_table step 4 where unload starts only if scene is loaded).

Is unloading a scene synchronous or asynchronous?

Unloading is asynchronous, meaning it happens in the background without freezing the game (see execution_table step 4 and 5).

Visual Quiz - 3 Questions

Look at the execution table, what is the scene state immediately after calling LoadScene?

A Loading

B Loaded and Active

C Not Loaded

D Unloading

💡 Hint

Check execution_table row 1 and 2 for scene state changes after LoadScene call.

At which step does the scene become ready for use?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at execution_table step where scene state is 'Loaded and Active'.

If you skip calling UnloadSceneAsync, what happens to the scene state?

A Scene goes to Unloading state

B Scene becomes Not Loaded automatically

C Scene stays Loaded and Active

D Scene reloads again

💡 Hint

Refer to variable_tracker and execution_table steps 4-6 about unloading process.

Concept Snapshot

Scene loading and unloading in Unity:
- Use SceneManager.LoadScene("SceneName") to load a scene.
- Scene loads assets then becomes active.
- Use SceneManager.UnloadSceneAsync("SceneName") to unload asynchronously.
- Scene state changes: Not Loaded -> Loading -> Loaded and Active -> Unloading -> Not Loaded.
- Unloading frees memory without freezing the game.

Full Transcript

This visual execution shows how Unity loads and unloads scenes step-by-step. First, LoadScene is called, which starts loading the scene assets. Once loaded, the scene becomes active and ready to use. Later, UnloadSceneAsync is called to remove the scene from memory asynchronously. The scene state changes from Not Loaded to Loading, then Loaded and Active, then Unloading, and finally back to Not Loaded. This process helps manage game memory and scene transitions smoothly.