Why does my GameMaker Tween on_complete callback never run?

Tweens are tied to the owning instance. If the instance is destroyed or deactivated before the tween completes, the callback is dropped. Make the owner persistent or store tweens on a controller object that survives the duration.

How do I keep a tween alive across rooms in GameMaker?

Run the tween from a persistent controller object, not from a per-room instance. Or save the tween id, manually update via TweenStep in your global controller's Step event, and trigger callbacks centrally.

Why does my chained tween skip the second step?

Chained tweens use TweenChain or composition; if the chain definition is malformed (missing TweenSpeed call, wrong delay), only the first step runs. Verify each step has its own definition and they are linked correctly.

Fix: GameMaker Tween Library Callback Not Firing

Quick answer: Tweens are owned by the instance that created them. If that instance is destroyed or its room ends before completion, callbacks are dropped. Run long-lived tweens from a persistent controller object.

Here is how to fix GameMaker Tween library on_complete callbacks that never fire. The tween animates correctly but the completion callback never runs because the owning instance was freed early.

The Symptom

You start a tween (TweenFire or via TweenManager). Visual animates. on_complete callback never executes. No errors.

What Causes This

Owner destroyed. Instance freed before tween completes.

Room change. Non-persistent instances are wiped on room change.

Wrong scope. Callback references “self” that points at the destroyed instance.

The Fix

Step 1: Run from a persistent controller.

// In oController Create event
persistent = true;

// Trigger the tween from oController, not the destroyed instance
TweenFire(oController, EaseOutQuad, 0, 0, 1, "x", 100, 200);

Step 2: Use TweenCallSelf for callbacks.

var _t = TweenFire(id, EaseOutQuad, 0, 0, 1, "x", x, x + 100);
TweenCallback(_t, TWEEN_EV_FINISH, on_arrived);

function on_arrived() {
    show_debug_message("Tween done");
}

TweenCallback registers handlers for events; survives as long as the tween itself.

Step 3: Validate instance before callback runs.

function on_arrived() {
    if (!instance_exists(self)) exit;
    // safe to use self
}

Step 4: For per-instance tweens, kill on destroy.

// Destroy event
TweenDestroy(my_tween);

Cleans up registered tweens to avoid lingering callbacks.

Step 5: Use the GMS2 built-in animation curve as alternative. For simple tweens, GMS2’s native animcurve_get_channel + lerp by your Step time is more transparent than the Tween library.

“Persistent controller for long tweens. TweenCallback for events. Validate instance before use. Callbacks land.”

Related Issues

For shader uniforms, see Shader Uniform Per Frame. For surface lifecycle, see Surface Lost.

Persistent owner. TweenCallback. instance_exists guard. Tween events fire.