Enemy Patrolling - Blueprint Runtime Error: "Accessed None trying to read property CallFunc_GetBlackboard_ReturnValue".

OculusEnglish · December 15, 2024, 2:01am

Hi all,

I am following along with the book Blueprints Visual Scripting for Unreal Engine 5 (3rd edition) Using Unreal Editor 5.0.3, as the book states to use Engine version 5.0.

I am having trouble in Chapter 9 creating enemy patrol points, on start up the enemy will not patrol between the two trigger spheres, and instead stays stationary. I have setup the BB_EnemyBlackboard, BP_EnemyCharacter, BP_EnemyController, and BT_EnemyBehaviour, and repeated the process three times and looked over several times to make sure I have not left anything out.

I receive the following error when trying to play the game. "Blueprint Runtime Error: “Accessed None trying to read property CallFunc_GetBlackboard_ReturnValue”. Node: Set Value as Object Graph: UpdatePatrolPointBB Function: Execute Ubergraph BP Enemy Character Blueprint: BP_EnemyCharacter"

I also have included a few screenshots. I notice in the event graph on the Event ActorBeginOverlap of the BP_EnemyCharacter the input pins on the equal functions are hollow, does this signal something is not quite right?

I have searched the forum a few years back, and although there was someone with the same problem, the fixes were not relevant to my situation.

If you have any suggestions, it would greatly help a newb out of this sticking point. Thanks

OculusEnglish · December 16, 2024, 1:47pm

bump

Auran131 · December 16, 2024, 2:00pm

its telling you that the CurrentPatrolPoint is Invalid, unless of course the KeyName is wrong

where do you Set/Validate PatrolPoint 1 + 2?

the keyname likely doesnt need to be a variable since it wont change? you can use MakeLiteral Name to set it

ClockworkOcean · December 16, 2024, 2:03pm

I think it’s the ‘get blackboard’ node returning nothing.

I can’t recall ( not at a machine rn ), but doesn’t it need an input, unless it’s in a behavior tree?

Auran131 · December 16, 2024, 2:07pm

good point, i’m pretty sure i’ve done it like that but it may need the AIController

ClockworkOcean · December 16, 2024, 2:07pm

ClockworkOcean · December 16, 2024, 2:14pm

Did you set the enemy character to spawn with an AI controller, in the details?..

OculusEnglish · December 17, 2024, 12:39am

Thanks for the useful suggestions. Patrol Point 1 and 2 refer to the trigger spheres, and are updated in the details of the variables created in the BP_EnemyCharacter Blueprint.

The blackboard does contain keys with a behaviour tree.

Changing the AI controlller class from BP_EnemyController to AI controller does not do anything for me.