Overriding OnPossess() with Unreal Engine 4.23.0

Recently Possess() has been deprecated from UE4, and when writing classes based on AAIController you have to use the function OnPossess().  When using the former vs the latter, you will have compilation problems, and potential breaks in the Artificial Intelligence for your various Pawns, and Blueprints, Blackboard, etc.

Above: AI Book I am currently reading. Quite insightful.

If you are using Blueprints, it's a matter of changing them. However you are using C++ code you must first do this in the header file (.h) of your class inheriting from AAIController:

 private: 

    UPROPERTY(transient)

    class UBlackboardComponent *BlackboardComp;

    

    UPROPERTY(transient)

    class UBehaviorTreeComponent *BehaviorComp;

   

 public:

   virtual void OnPossess(APawn *InPawn) override

  

    bool isDead = false;

    uint8 EnemyKeyID;

    uint8 PatrolKeyID;

    uint8 EnemyModeBBKeyID;

    uint8 isDeadBBKeyID;

    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "MoveEnemy")

Then in the implementation file (.cpp) file you implement like this:

 void AEnemyAI::OnPossess(APawn *InPawn) {

    Super::OnPossess(InPawn);

    AEnemyCharacter *Char = Cast<AEnemyCharacter>(InPawn);

    

    if (Char && Char->Enemy) {

        BlackboardComp->InitializeBlackboard(*Char->Enemy->BlackboardAsset);

        EnemyKeyID = BlackboardComp->GetKeyID("Target");

        PatrolKeyID = BlackboardComp->GetKeyID("PatrolTarget");

        EnemyModeBBKeyID = BlackboardComp->GetKeyID("EnemyModeBB");

        isDeadBBKeyID = BlackboardComp->GetKeyID("isEnemyDeadBB");

        tChar = Char;

        BehaviorComp->StartTree(*Char->Enemy);

    }

 }

Unity3D C# Enemy Find nearest Player Script

In this script which you attach to the Enemy Objects, you may find the nearest object Tagged "Player". The Enemy faces the Player, and chases within a proximity, with a given frequency. See below:

/// <summary>
/// AI character controller.
/// Just A basic AI Character controller
/// will looking for a Target and moving to and Attacking
/// </summary>

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(CharacterSystem))]

public class AICharacterController : MonoBehaviour {

    public GameObject ObjectTarget;
    public string TargetTag = "Player";
    private CharacterSystem character;
    private int aiTime = 0;
    private float scanFrequency = 1.0f;
    private int aiState = 0;

    void Start () {
        character = gameObject.GetComponent<CharacterSystem>();
        InvokeRepeating ("ScanForTarget",0,scanFrequency);
    }
   
    void ScanForTarget() {
        ObjectTarget = GetNearestTaggedObject();
    }

    public GameObject GetNearestTaggedObject () {
        var nearestDistanceSqr = Mathf.Infinity;
        GameObject nearestObj = null;

        foreach (var obj in GameObject.FindGameObjectsWithTag(TargetTag)) {

            var objectPos = obj.transform.position;
            var distanceSqr = (objectPos - transform.position).sqrMagnitude;
           
            if (distanceSqr < nearestDistanceSqr) {
                nearestObj = obj;
                nearestDistanceSqr = distanceSqr;
            }
        }
        return nearestObj;
    }

    public float DistanceSquaredTo(GameObject source, GameObject target) {
        return Vector3.SqrMagnitude(source.transform.position - target.transform.position);
    }

    void Update () {
            //if (GameObject.Find("CharacterDakota").GetComponent<CharacterStatus>().HP > 0) {
           
        if (GameObject.Find("GameManager").GetComponent<GameManager>().Playing) {

            var direction = Vector3.zero;
            if(aiTime<=0){
                aiState = Random.Range(0,4);
                aiTime = Random.Range(10,100);
            }else{
                aiTime--;
            }
            if(ObjectTarget){
                //ObjectTarget = GameObject.FindGameObjectWithTag(TargetTag);   
                float distance = Vector3.Distance(ObjectTarget.transform.position,this.gameObject.transform.position);
               
                if(distance<=2){
                    transform.LookAt(ObjectTarget.transform.position);
                    if(aiTime<=0){
                        if(aiState == 1){
                            character.Attack();
                        }
                    }
                }else{
                    if(aiState == 1){
                        transform.LookAt(ObjectTarget.transform.position);
                        direction = this.transform.forward;
                        direction.Normalize();
                        character.Move(direction);
                    }
                }
               
            }else{
                ScanForTarget();
            }
        }
    }
}