Скачать или смотреть Resolving the null Object Issue in Unity's Stack Handling

Dive into the intricacies of managing GameObjects in Unity, particularly how to effectively handle a Stack of GameObjects without losing references.
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This video is based on the question https://stackoverflow.com/q/62739098/ asked by the user 'Sven' ( https://stackoverflow.com/u/13869764/ ) and on the answer https://stackoverflow.com/a/62739150/ provided by the user 'Stefan' ( https://stackoverflow.com/u/2416958/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the null Object Issue in Unity's Stack Handling

As a game developer using Unity, you might find yourself wanting to manipulate GameObjects dynamically during gameplay. A common requirement is to read a GameObject's children into a Stack for later use, with plans to destroy them temporarily. However, many beginners encounter an issue: their GameObjects vanish because they turn into null once the game objects are destroyed. Let's explore why this happens and how to work through it.

The Problem

Imagine you have a GameObject with various child objects that you want to store temporarily in a Stack. You intend to destroy these objects (so they're no longer visible), but later on, you want to retrieve and re-display them by popping them off the Stack. Yet, after popping, you find that the objects are all null. Why is this happening?

Understanding the Code

Here's the snippet of code that's giving you trouble:

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

Key Observations

Pushing Objects to the Stack: When you call aufgenommeneKarten.Push(parent.transform.GetChild(i).gameObject); you are pushing the reference to the GameObject. However, immediately afterward, you call Destroy(...) on the same GameObject, which will destroy the instance in your game. Consequently, while the reference is still in the Stack, the actual object it refers to is no longer valid, hence leading to null references when you attempt to pop them later.

Validations: Before pushing objects onto your Stack, it is advisable to validate whether parent.transform.GetChild(i).gameObject is indeed not null. This ensures that you're only working with valid objects.

Stack Management Logic: The line stacked = !stacked; actively controls the stack's state, but setting it explicitly can sometimes lead to bugs. Consider managing the state in a more controlled manner.

Recommended Solutions

To solve the problem you are facing and ensure significant robustness while handling your Stack, consider the following adjustments:

1. Avoid Destroying Objects Immediately

Instead of destroying the GameObjects right after pushing them onto the Stack, it may be better to disable them instead:

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

By deactivating, you won't lose the reference in your Stack, and you can reactivate them later.

2. Validate before Pushing

Before pushing the GameObjects onto your Stack, always check if they are invalid or null:

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

This prevents null references from entering your Stack in the first place.

3. Simplify the Pop Logic

Remove unnecessary lines, such as the instantiation of a new GameObject, before the pop action. Instead, directly pop the GameObject from the Stack:

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

Conclusion

To effectively manage your GameObjects in Unity while using a Stack, remember to handle object destruction wisely. Utilize deactivation instead of immediate destruction, validate your objects, and streamline your Stack management logic. These tips will help you avoid the common pitfalls of losing object references, allowing for a more seamless development experience.

By following this guide, you should be able to resolve the null reference issue in your Unity project and enjoy a smoother workflow when managing GameObjects dynamically.