AUR0502

Error Message

AUR0502: Trying to activate a disposed controller: <ControllerName>

Where <ControllerName> is the name of the controller (often derived from the component's name) that was already disposed.

Description

This error occurs when Aurelia's rendering engine attempts to activate a component's controller (part of the process of rendering and attaching the component), but finds that the controller instance has already been marked as disposed.

Cause

This situation typically arises from incorrect manual manipulation of component lifecycles or asynchronous operations that complete after a component has been removed. Common causes include:

1. Premature Disposal: Manually calling the controller's dispose() method or related disposal logic prematurely, before Aurelia has finished its deactivation sequence or while an activation is pending.

2. Race Conditions: An asynchronous operation related to component activation (e.g., fetching data needed for the component) completes, and its callback attempts to proceed with activation steps, but the component was deactivated and disposed in the meantime (e.g., user navigated away quickly).

3. Reusing Disposed Controllers: Attempting to reuse a controller instance that has already gone through its disposal lifecycle. Controller instances are generally meant to be used once per component instantiation.

4. Incorrect Lifecycle Management: Custom logic that interferes with Aurelia's standard activation/deactivation flow might lead to controllers being disposed while still being considered for activation.

Solution

1. Avoid Manual Disposal (Usually): Do not manually call controller.dispose() unless you have a very specific reason and fully understand the lifecycle implications. Let Aurelia manage the disposal as part of its standard deactivation process.

2. Handle Asynchronous Activation Safely: If activation involves asynchronous operations, ensure that callbacks or subsequent steps check if the controller/component is still active before proceeding. Often, Aurelia's lifecycle hooks (detaching, unbinding) can be used to cancel pending operations or set flags indicating the component is no longer active.

3. Do Not Reuse Controllers: Treat controller instances as single-use. When a component is re-rendered or navigated back to, Aurelia will typically create a fresh controller instance.

4. Review Custom Lifecycle Logic: If you have custom code interacting with component controllers or lifecycles, ensure it doesn't conflict with Aurelia's internal state management. Check for places where dispose might be called inappropriately.

Example

import { customElement, ICustomElementController } from 'aurelia';

@customElement({ name: 'my-data-component', template: 'Loading...' })
export class MyDataComponent {
  public data: unknown = null;
  public controller!: ICustomElementController<this>;
  private isAttached = false;
  private abortController = new AbortController();

  public attaching() {
    this.isAttached = true;
    this.loadData();
  }

  public detaching() {
    this.isAttached = false;
    // Cancel any pending fetch if the component is detached
    this.abortController.abort();
  }

  async loadData() {
    try {
      const response = await fetch('/api/data', { signal: this.abortController.signal });
      if (!this.isAttached) return; // Check if still attached before processing

      this.data = await response.json();
      // If activation logic continued here after disposal, it could potentially lead to issues,
      // though AUR0502 specifically relates to the *start* of the activation process.
      // A more likely scenario for *related* errors is trying to update state after disposal.
      console.log('Data loaded');

      // --- Hypothetical scenario leading to AUR0502 ---
      // Imagine some external code held a reference to this.controller
      // and incorrectly tried to call controller.activate(...) *again* after
      // the component was detached and disposed.
      // someExternalReferenceToController.activate(someActivationContext); // Could cause AUR0502
      // ---------------------------------------------

    } catch (error) {
      if ((error as Error).name === 'AbortError') {
        console.log('Fetch aborted during detach.');
      } else if (this.isAttached) {
        console.error('Failed to load data:', error);
      }
    }
  }
}

// Potential problematic external code (Illustrative)
// let controllerRef: ICustomElementController | null = null;
//
// // In some component's attached hook:
// // controllerRef = this.controller;
//
// // Later, possibly after the original component is gone:
// function tryReactivating() {
//   if (controllerRef) {
//     try {
//       // If controllerRef points to a disposed controller, this might trigger AUR0502
//       // Note: Manually calling activate like this is usually incorrect.
//       controllerRef.activate(controllerRef /* simplified args */);
//     } catch (e) {
//       console.error("Error trying to reactivate:", e); // Might be AUR0502
//     }
//   }
// }

Debugging Tips

• Identify which component's controller is causing the error (<ControllerName>).

• Examine the code paths leading to the activation attempt. Is it part of the standard Aurelia rendering process, or is it triggered by custom code?

• Look for any custom code that might be calling controller.dispose() or methods that lead to disposal.

• Set breakpoints in the component's lifecycle hooks (dispose, detaching, unbinding) and the code attempting activation to understand the sequence of events.

• Analyze asynchronous operations within the component's lifecycle methods (activate, binding, bound, attaching). Ensure they handle cancellation or check the component's status before proceeding upon completion.