unity dont destroy on load with code examples

As a game developer, one of the most common challenges you face is managing game objects between scenes. Unity, the popular game engine, provides a convenient feature called "Don't Destroy on Load" that lets you retain objects across scenes. This feature is very useful, but it also comes with its own set of challenges. In this article, we will explain how to use "Don't Destroy on Load" efficiently and minimize its potential issues.

What is "Don't Destroy on Load"?

In Unity, when a new scene is loaded, all active game objects in the current scene are destroyed. This behavior is often a desirable feature since it helps maintain the game's performance by freeing up resources from the previous scene. However, some game objects, like the player or key game items, must persist between scenes. In such cases, Unity's "Don't Destroy on Load" feature can be useful.

Simply put, "Don't Destroy on Load" is a Unity command that prevents a game object from being destroyed when a new scene is loaded. When a game object is marked as "Don't Destroy on Load," it will continue to exist even if the scene changes. This feature is useful when you want to keep essential objects available between scenes.

How to use "Don't Destroy on Load" in Unity

Here's how you can use "Don't Destroy on Load" in Unity:

Step 1: Select the game object that you want to retain between scenes.

Step 2: Open the script that contains the code for the game object.

Step 3: Add the following line of code in the script's Start method:

DontDestroyOnLoad(gameObject);

This line of code will mark the selected game object as "Don't Destroy on Load." Once your script is executed, the marked game object will continue to exist throughout your game's lifecycle.

Example Usage

Let's consider an example to illustrate the practical use of "Don't Destroy on Load." Suppose we have a game where the player has a grapple gun that can be used to swing across levels. We want the player's grapple gun to remain available between scenes, so the player does not lose progress. To achieve this, we'll need to use "Don't Destroy on Load."

Here's how you'd implement this in Unity:

Step 1: Create a new Unity project and add two scenes: the main menu and the game scene.

Step 2: In the first scene, add a button that will take the player to the game scene. Add the following on-click event to the button:

SceneManager.LoadScene("GameScene");

This code will load the second scene when the button is clicked.

Step 3: Add the following script to the Grapple Gun game object:

using UnityEngine;
using UnityEngine.SceneManagement;

public class GrappleGun : MonoBehaviour
{
    void Start()
    {
        DontDestroyOnLoad(gameObject);
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Escape))
            SceneManager.LoadScene("MainMenu");
    }
}

This script will make sure that the GrappleGun game object is not destroyed when the player moves between scenes.

Step 4: Create a new scene named "GameScene" and add a Text object that will display the current scene's name.

Step 5: Add the following script to the Text object:

using UnityEngine;
using UnityEngine.UI;

public class SceneName : MonoBehaviour
{
    void Start()
    {
        GetComponent<Text>().text = SceneManager.GetActiveScene().name;
    }
}

This script will retrieve the current scene's name and display it on the Text object.

Step 6: Test the game by starting from the main menu and navigating to the game scene. Once in the game scene, you can use the Escape key to return to the main menu. The GrappleGun game object will remain available throughout the game, and you can swing around different levels without losing progress.

Potential Issues with "Don't Destroy on Load"

While the "Don't Destroy on Load" feature is useful, it comes with a few potential issues that you need to watch out for. Here are some of the problems you might encounter:

  1. Memory Leaks: If you mark several game objects as "Don't Destroy on Load," you might encounter memory leaks. This issue is sporadic since the game objects continue to exist between scenes, consuming more memory with each new level.

  2. Unwanted Repetitions: If you mark game objects as "Don't Destroy on Load," they might be affected by multiple scripts. This problem can cause the same game object to appear in several places, leading to confusion.

  3. Compatibility Issues: If you're building a large project with many game objects marked as "Don't Destroy on Load," you might encounter compatibility issues when sharing your project with other developers.

To avoid these issues, make sure that you only mark essential game objects as "Don't Destroy on Load" and test your game thoroughly before release.

Conclusion

Unity's "Don't Destroy on Load" feature is a powerful tool that can help you maintain game objects between scenes. However, use this feature carefully, as it comes with potential issues. As a game developer, it's your responsibility to build efficient code and thoroughly test your game to ensure a seamless experience for your players. Now that you understand how "Don't Destroy on Load" works, you can use it to enhance your game's continuity.

Sure thing!

Memory Leaks

Memory leaks can occur when you mark multiple game objects as "Don't Destroy on Load." The game objects that are not destroyed can consume more memory as new levels are loaded, causing the game to slow down or crash. To prevent this problem, you can follow these best practices:

  1. Mark only essential game objects as "Don't Destroy on Load."

  2. If a game object is no longer needed, destroy it explicitly by calling Destroy(gameObject) in your script.

  3. Use Unity's profiling tools (e.g., the Memory Profiler) to detect memory leaks and optimize your game's performance.

Unwanted Repetitions

Unwanted repetitions can occur when you mark a game object as "Don't Destroy on Load," and it's affected by multiple scripts. For example, suppose you have a "Player" game object that's marked as "Don't Destroy on Load," and it's affected by multiple scripts that each spawn a new "Player" object. In that case, you might end up with multiple "Player" objects in different parts of your game, leading to confusion.

To solve this problem, you can mark only the essential script that controls the "Player" object as "Don't Destroy on Load." You can use the GetComponent method to retrieve the essential script and mark only that script as "Don't Destroy on Load." This will ensure that the "Player" game object is not affected by multiple scripts, preventing unwanted repetitions.

Compatibility Issues

Compatibility issues can arise when you work in a large project with multiple developers or team members. If you mark several game objects as "Don't Destroy on Load," you might encounter compatibility issues when other developers try to work on your project.

To avoid compatibility issues, you can follow these best practices:

  1. Use comments to document which game objects are marked as "Don't Destroy on Load" in your scripts.

  2. Use version control tools like Git to manage your code changes.

  3. Test your game thoroughly before release to catch any compatibility issues early.

Conclusion

"Don't Destroy on Load" is a useful Unity feature that can help you maintain important game objects between scenes. However, it's essential to use this feature carefully because it can cause issues like memory leaks, unwanted repetitions, and compatibility problems. By following the best practices discussed in this article, you can avoid these issues and use "Don't Destroy on Load" to enhance your game's continuity. Remember, as a game developer, it's your responsibility to build efficient, stable, and reliable code to create an enjoyable gaming experience for your players.

Popular questions

  1. What does "Don't Destroy on Load" do in Unity?
    Answer: "Don't Destroy on Load" is a Unity feature that prevents a game object from being destroyed when a new scene is loaded. This means that if a game object is marked as "Don't Destroy on Load," it will continue to exist even if the scene changes.

  2. How do you mark a game object as "Don't Destroy on Load" in Unity?
    Answer: To mark a game object as "Don't Destroy on Load" in Unity, you can add the following line of code in the script's Start method: DontDestroyOnLoad(gameObject). This line of code will ensure that the selected game object is not destroyed when a new scene is loaded.

  3. What are some potential issues with using "Don't Destroy on Load" in Unity?
    Answer: Some potential issues with using "Don't Destroy on Load" in Unity include memory leaks, unwanted repetitions, and compatibility problems. To avoid these issues, you should only mark essential game objects as "Don't Destroy on Load" and test your game thoroughly before release.

  4. Can you explicitly destroy a game object that's marked as "Don't Destroy on Load" in Unity?
    Answer: Yes, you can explicitly destroy a game object that's marked as "Don't Destroy on Load" by calling Destroy(gameObject) in your script. This will destroy the game object and free up memory, ensuring that it's no longer a potential memory leak source.

  5. How can you prevent unwanted repetitions when marking game objects as "Don't Destroy on Load" in Unity?
    Answer: To prevent unwanted repetitions when marking game objects as "Don't Destroy on Load" in Unity, you can mark only the essential script that controls the game object as "Don't Destroy on Load." You can retrieve the essential script using the GetComponent method and mark only that script as "Don't Destroy on Load." This will ensure that the game object is not affected by multiple scripts, preventing unwanted repetitions.

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