Handling Interrupted States during Pathfinding

In this lesson, you will learn how to detect and gracefully resolve AI state transitions when external forces—like knockbacks, physics collisions, or dynamic navigation changes—interrupt a character’s active pathfinding.

The Problem of Stale Pathing

When your AI is executing a MoveTo task, it relies on a calculated path. If an external force moves the AI, or if the navigation mesh changes (e.g., a door closes or a platform shifts), the AI’s current path may become invalid. If you don't explicitly handle these interruptions, the AI might get "stuck" trying to walk through an obstacle or entering a glitched state where it thinks it is still moving toward a stale destination.

Implementation Strategy

To handle this, we utilize the OnMoveCompleted delegate provided by the AAIController. When a move is interrupted, the EPathFollowingResult will return Interrupted. You must capture this in your C++ controller or your custom Task node to trigger a state machine transition.

void AMyAIController::OnMoveCompleted(FAIRequestID RequestID, const FPathFollowingResult& Result)
{
    Super::OnMoveCompleted(RequestID, Result);

    if (Result.Code == EPathFollowingResult::Interrupted)
    {
        // 1. Notify our state machine that the current goal is invalid
        StateComponent->SetState(EAIState::Recovering);
        
        // 2. Clear stale Blackboard keys to prevent loop re-entry
        Blackboard->ClearValue(TargetLocationKey);
        
        // 3. Re-evaluate using EQS to find a new viable position
        RunBehaviorTree(BehaviorTreeAsset);
    }
}

Best Practices for Interruption

1. Immediate State Reset: Always move the AI into a "Recovery" or "Idle" state immediately upon interruption. This prevents the Behavior Tree from fighting against the physical impulse that caused the interruption.
2. Path Validation: In your Tick or via a Timer, periodically check GetPathFollowingComponent()->HasValidPath(). If it returns false while the AI is in a "Moving" state, force a state transition to "Searching" to re-calculate a path from the new position.
3. Blackboard Synchronization: Ensure your Blackboard keys are cleared during an interruption; otherwise, the AI may attempt to navigate to the exact same point that caused the obstruction or collision.

Key Takeaway: Always intercept the EPathFollowingResult::Interrupted code to reset your AI state machine, clear Blackboard targets, and force a fresh EQS re-evaluation before resuming movement.