Dynamically alocated data in OnConstruct() - pointer nullified

Development Programming & Scripting C++
1

Hi,

In short: how to prevent from loosing a pointer to data that is dynamically generated in OnConstruct() method? Pointer is NULL during gameplay, but holds a proper addres in editor.

This post looks big but I believe the content is very simple :slight_smile: I guess it’s a beginner question I have that most of you knows the answer to. I was wondering if you could please explain how to proceed in cases like mine.

I have my custom class which currently doesn’t inherit from any UE4 classes:


class MyData
{
	...
};

I have my custom actor based class that has a property of pointer to MyData:


class ... AMyActor : public AActor
{
	...
	
	MyData* pointer;
	void OnConstruct(...)
	{
		pointer = new MyData();
	}
};

As you can see dynamic creation of MyData instance takes place in OnConstruct(), which means that I already have the instance in UEditor, which is important to me.

Now, there is a problem: I noticed that when I launch a game, the pointer gets null’ified. I’m looking for a solution to prevent that.
I read about garbage collecting and stuff and I figured out some solutions. I’d be grateful to hear your opinions which way is better or if any of them is good at all.

Method 1 - Using FGCObject:

I add FGCObject to inheritance list of AMyActor class and mark the pointer with special method, like this:


class ... AMyActor : public AActor, **public FGCObject**
{
	...
	
	MyData* pointer;
	void OnConstruct(...)
	{
		pointer = new MyData();
	}
	
**	void AddReferencedObjects(FReferenceCollector& Collector) override
	{
		Collector.AddReferencedObject(pointer);
	}**
};

I’m not sure if mixing AActor and FGCObject together in the base of my actor class won’t cause any troubles… I already tried this and got some strange error messages during compilation, but I’m still fighting this. Not sure if this even prevents the pointer from being zeroed…

Method 2 - Using UOBject:

I add FGCObject to inheritance list of MyData class:


class MyData : **public UOBject**
{
	...
};

And thanks to this, hopefully, I will be able to use UPROPERTY() above the declaration of my pointer:


class ... AMyActor : public AActor
{
	...
	
	**UPROPERTY()**
	MyData* pointer;
	
	void OnConstruct(...)
	{
		pointer =** NewObject**<MyData>();
	}
};

I noticed that using UPROPERTY() prevents from losing pointer value, but it requires the pointer to be of one of UE4 specific types.

Method 3 - … i haven’t found yet … any suggestions what to look for?

2

MMm declared as SharedRef<> inside GameInstance singleton?, what you are trying to do?, perhaps you need use FFactory if you want create your own Data Asset, if it not your actual Method 2 looks fine for me, construct script is just able to Modify a variable in Editor for example to produce some behavior, but not for storing data like that, because each time you hit play, you are constructing instances from scratch.

3

Thank you ZkarmaKun for your suggestions.
I don’t think using GameInstance is a good way as it’s instsance does not exist until gameplay.

Regarding method 2:
I discovered that not only do I need to put UPROPERTY() above pointer declaration, but also above every AMyData parameter that I want to maintain it’s value to gameplay.
I’d be good to see some official info that this is the way it is suppose to work and it’s not gonna change in future version. I only found that UPROPERTY() prevents from garbage collecting but to me it’s not equivalent with saving values between editor and gameplay time.