Spawning BP Class from C++ error : SpawnActor failed because no class was specified

Development Programming & Scripting C++
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1

In Project Settings I have set GameMode to → HOMM3GameMode_BP

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In this HOMM3GameMode_BP I have set Grid Class to Grid_BP

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Then In BeginPlay of HOMM3GameMode I have this spawning code

void AHOMM3GameMode::BeginPlay()
{
	Super::BeginPlay();
	UWorld* MyLevel = GetWorld();

	if (IsValid(MyLevel))
	{
		const FVector Location(0.0f, 0.0f, 0.0f);
		const FRotator Rotation(0.0f, 0.0f, 0.0f);
		FActorSpawnParameters SpawnInfo;
		SpawnInfo.SpawnCollisionHandlingOverride = ESpawnActorCollisionHandlingMethod::AlwaysSpawn;		
		AActor* Spawned = MyLevel->SpawnActor<AActor>(GridClass, Location, Rotation, SpawnInfo);
		
		Grid = Cast<AGrid>(Spawned);
		
		if (IsValid(Grid))
		{
			UE_LOG(LogTemp, Warning, TEXT("Spawned successfully! New Actor: %s"), *Grid->GetName());
		}
	}
}

What happens is I get → “SpawnActor failed because no class was specified”.
I believe I have made sure that correct GameMode_BP is in Project Settings, and in GameMode I have set correct Class to be spawned.

2

Hi,

Try changing “GridClass” to “GridClass->GetClass()” in the SpawnActor…

3

you could add a BeginPlay in your GameMode Blueprint and add a Print Text there to see if that’s being executed.
I would guess that you’re not running the game mode blueprint, but rather running the base.

You could also declare your game mode as abstract, so it can’t be instanced incorrectly.

4

I will try this. When I tried to use “GridClass->GetClass()” I get crash, it does seem logical that it is running C++ version of GameMode.

5

Header

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/GameModeBase.h"
#include "HOMM3GameMode.generated.h"

/**
 * 
 */
UCLASS()
class YOUR_API AHOMM3GameMode : public AGameModeBase
{
	GENERATED_BODY()
	public:
		UPROPERTY(EditDefaultsOnly,Category="Grid Class")
		TSubclassOf<class AGrid> GridClass;
		virtual void BeginPlay() override;	
};

CPP


#include "HOMM3GameMode.h"
#include "Grid.h"

void AHOMM3GameMode::BeginPlay()
{
	Super::BeginPlay();
	UWorld* MyLevel = GetWorld();

	if (IsValid(MyLevel))
	{
		const FVector Location(0.0f, 0.0f, 0.0f);
		const FRotator Rotation(0.0f, 0.0f, 0.0f);
		FActorSpawnParameters SpawnInfo;
		SpawnInfo.SpawnCollisionHandlingOverride = ESpawnActorCollisionHandlingMethod::AlwaysSpawn;
		if (GridClass != nullptr) {
			AGrid* Spawned = MyLevel->SpawnActor<AGrid>(GridClass, Location, Rotation, SpawnInfo);
			if (Spawned != nullptr)
			{				
				if (GEngine)
					GEngine->AddOnScreenDebugMessage(-1, 5, FColor::Emerald, "Spawned successfully!New Actor :"+ Spawned->GetName());
			}
		}
	}
}

There is no need for casting just spawn directly to AGrid. Also you missed a null check to see if the tsub of grid is set

6

It might be possible that that’s it, just SpawnActor throwing an error when realizing it’s being asked to spawn an AActor out of an AGrid .

7

This wont report any logs nor spawn, but I think you are correct with this code, it should work.

I think GridClass is nullptr, and that is because GameMode is “HOMM3GameMode” not “HOMM3GameMode_BP”. BP version has GridClass set, I dont know why it is running the base version of GameMode instead of _BP because I have set it to use _BP in Project Settings.

Also in OutpuLog it reads

LogLoad: Game class is 'HOMM3GameMode'

It should be HOMM3GameMode_BP ?

8

I also tried to log message in HOMM3GameMode_BP at BeginPlay and this wont log. So I’m pretty sure it’s using C++ version of GameMode, ignoring that I have it set to BluePrint version in ProjectSettings. I dont know how to fix that

9

FYI My code spawns the agrid actor with no problems reporting it as the bp implementation.

10

I created new BluePrint from HOMM3GameMode, named it TESTMODEBP and set it in ProjectSettings.
I ran game and still it reads in OutputLog

LogLoad: Game class is 'HOMM3GameMode'

For some reason it seems to be stuck on base Class of my GameMode instead of BP versions

11

I went to “World Settings” and put GameMode override to my BluePrint versions and after that everything works!
Beats me why it didnt work through ProjectSettings

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12

Perhaps you set the c++ version of your game mode class in your project settings (which has an uninitialized tsubof variable) in place of the bp version where it is set?

13

I think at some point I mustve accidentally set in the World Settings → Game Mode Override, my C++ GameMode Class. It seems once this was set, it didnt matter what was in Project Settings.
Now I changed World Settings → Game Mode Override to None, and now Project Settings works again. What I choose now as default in Project Settings will be used.

As to when / why I had put the World Settings → Game Mode Override to C++ Class I do not know. Probably at the start of the project I looked at World Settings and maybe there I set it accidenttaly.

But thank you for replies! As a plus you showed me a cleaner version of my spawning code :slight_smile: