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Learn how to implement a robust enemy persistence system in Unity that ensures `killed enemies` do not respawn after reloading scenes. Discover the best practices for saving and loading game states efficiently.
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Efficiently Manage Enemy Persistence in Unity: Keep Killed Enemies Gone After Reloading

One of the challenges in video game development is creating a seamless experience where the game state reflects the player's actions. For many developers, particularly those new to Unity, the concept of persisting certain game states can feel overwhelming. How can you ensure that once an enemy is defeated, it stays defeated even after reloading a scene?

In this guide, we will discuss an effective solution to this common problem, allowing you to keep track of killed enemies in your game without sacrificing performance.

Understanding the Problem

When players defeat enemies in your game, having those enemies reappear can be frustrating. A simple approach might suggest saving each enemy's state to a file, especially if they are assigned a unique ID. However, constantly writing to and reading from a file can severely impact your game's performance.

Our Goal

To prevent killed enemies from respawning after reloading a scene.

To implement an efficient system that doesn't bog down the game with frequent disk access.

A More Efficient Solution

Utilize a Persistent Script

Instead of saving enemy states to a file every time an enemy is killed, consider creating a persistent script that exists across scenes. Here’s how it works:

Create a Persistent GameObject:

Use DontDestroyOnLoad to ensure this object remains active when transitioning between scenes.

Implement a Static HashMap or Dictionary:

This will act as your database in memory to track killed enemies. You can use the unique IDs of those enemies as keys in your dictionary.

Benefits of a HashMap

Efficiency: A HashMap or Dictionary allows for constant time complexity (O(1)) for both insertions and lookups. This means that the performance of your enemy persistence won't degrade as the number of enemies grows.

In-Memory Storage: Since this data is stored in memory, there is no need for redundant file operations every time an enemy is killed or a scene is reloaded.

Implementation Steps

Step 1: Create Your Persistent Script

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Update Enemy States

Whenever an enemy is killed, you must call the EnemyKilled method from the EnemyPersistence script:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Scene Reload Handling

In your scene loading logic, check the killedEnemies dictionary to see if an enemy should remain dead:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Save and Load Between Sessions

When players save and load their game, serialize the contents of the HashMap to a file, so you can maintain their state:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following this approach, you can effectively manage enemy persistence in your Unity game without the downsides of frequent file operations. Utilizing a persistent script with a HashMap equips you with an efficient and refined solution to keep killed enemies gone, enhancing your game's performance and overall player experience.

Now it’s time to implement this strategy in your game and create a seamless experience for your players!