[BUG] FSM error when using DestroyGameObject ActionTask.

This topic has 0 replies, 2 voices, and was last updated 6 years ago by Gavalakis.

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April 18, 2020 at 1:04 am #16376

guyboots_thunderbro

Participant

This exception happens when using Destroy GameObject on the current agent:

NullReferenceException: Object reference not set to an instance of an object

NodeCanvas.StateMachines.FSM.OnGraphUpdate () (at Assets/ParadoxNotion/NodeCanvas/Modules/StateMachines/FSM.cs:90)

NodeCanvas.Framework.Graph.UpdateGraph (System.Single deltaTime) (at Assets/ParadoxNotion/CanvasCore/Framework/Runtime/Graphs/Graph.cs:687)

NodeCanvas.Framework.Graph.UpdateGraph () (at Assets/ParadoxNotion/CanvasCore/Framework/Runtime/Graphs/Graph.cs:680)

ParadoxNotion.Services.MonoManager.Update () (at Assets/ParadoxNotion/CanvasCore/Common/Runtime/Services/MonoManager.cs:98)

At the line in the stack trace, currentState is null. It becomes null after FSM.cs:84, currentState.Update(). FSM.cs:76 does a null check, but it’s too early, or maybe there needs to be another?

Using NodeCanvas 3.0.5. Unity 2019.3.10f.

April 18, 2020 at 2:58 pm #16382

Gavalakis

Keymaster

Hello,

Just to clarify, is the Destroy GameObject call happening from within the update of the FSM itself, or from some other part of your code?

Thanks.

April 18, 2020 at 6:34 pm #16381

guyboots_thunderbro

Participant

> Just to clarify, is the Destroy GameObject call happening from within the update of the FSM itself, or from some other part of your code?

Using the Action Task Destroy GameObject.

April 19, 2020 at 9:19 pm #16380

guyboots_thunderbro

Participant

I’ve attached a screenshot.

April 26, 2020 at 11:52 am #16379

Gavalakis

Keymaster

Hello,

Yeah, this is an edge case because the FSM is destroyed from within it’s own update. Here is quick fix though. Please open up FSM.cs and completely change the method named ‘OnGraphUpdate’ with the following code:

protected override void OnGraphUpdate() {

if ( currentState != null ) {

//Update defer updatables (basically AnyStates and ConcurentStates)

for ( var i = 0; i < updatableNodes.Count; i++ ) {

updatableNodes[i].Update();

}

//this can only happen if FSM stoped just now (from the above update)

if ( currentState == null ) { Stop(false); return; }

//Update current state

currentState.Update();

if ( onStateUpdate != null && currentState.status == Status.Running ) {

onStateUpdate(currentState);

}

//this can only happen if FSM stoped just now (from the above update)

if ( currentState == null ) { Stop(false); return; }

//state has nowhere to go..

if ( currentState.status != Status.Running && currentState.outConnections.Count == 0 ) {

//...but we have a stacked state -> pop return to it

if ( stateStack.Count > 0 ) {

var popState = stateStack.Pop();

EnterState(popState, TransitionCallMode.Normal);

return;

}

//...and no updatables -> stop

if ( !updatableNodes.Any(n => n.status == Status.Running) ) {

Stop(true);

return;

}

//if null state, stop.

if ( currentState == null ) {

Stop(false);

return;

}

Let me know if that quickfix works for you.
Thanks 🙂

April 26, 2020 at 8:59 pm #16378

guyboots_thunderbro

Participant

I have identical changes here locally, so can confirm this works.

May 2, 2020 at 11:44 am #16377

Gavalakis

Keymaster

Great.
Thanks for confirming and I am glad the change was the same 🙂

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