microg/GmsCore · error · UnsupportedOperationException

addOnCanceledListener is not implemented

Error message

addOnCanceledListener is not implemented

What it means

Task.addOnCanceledListener(OnCanceledListener) is declared in this library's abstract Task class but not implemented; it unconditionally throws UnsupportedOperationException 'addOnCanceledListener is not implemented'. Subclasses are expected to override it; calling it on the base/default implementation always fails.

Solutions

  1. Upgrade to a library version whose concrete Task classes implement addOnCanceledListener
  2. Avoid addOnCanceledListener; use addOnCompleteListener and check task.isCanceled() instead
  3. Wrap in try-catch for UnsupportedOperationException if cancel notification is optional
  4. Use a fully implemented Task subclass (e.g. Task from a real TaskCompletionSource flow)

Example fix

// before
task.addOnCanceledListener(listener); // throws
// after
task.addOnCompleteListener(t -> {
    if (t.isCanceled()) listener.onCanceled();
});
Defensive patterns

Strategy: try-catch

Try / catch

try {
    task.addOnCanceledListener(listener);
} catch (UnsupportedOperationException e) {
    task.addOnCompleteListener(t -> { if (t.isCanceled()) listener.onCanceled(); });
}

Prevention

When it happens

Trigger: Registering a cancel listener via the single-argument overload on any Task instance that inherits the base implementation (e.g. a Task returned by an API that does not override this method).

Common situations: Using this library's play-services-tasks port (e.g. microG) and adding cancel listeners as in official Google Play Services code; the port lacks the override in the Task implementation being used.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of microg/GmsCore@157c9d86ac (2026-09-06). Data as JSON: /api/errors/1fc3a4200c705473. Report an issue: GitHub.

Appendix: source

Thrown at play-services-tasks/src/main/java/com/google/android/gms/tasks/Task.java:34

/**
 * Represents an asynchronous operation.
 */
@PublicApi
public abstract class Task<TResult> {

    public Task() {
    }

    /**
     * Adds a listener that is called if the Task is canceled.
     * <p>
     * The listener will be called on main application thread. If the Task has already been canceled, a call to the listener will be immediately scheduled. If multiple listeners are added, they will be called in the order in which they were added.
     *
     * @return this Task
     */
    public Task<TResult> addOnCanceledListener(OnCanceledListener listener) {
        throw new UnsupportedOperationException("addOnCanceledListener is not implemented");
    }

    /**
     * Adds a listener that is called if the Task is canceled.
     * <p>
     * If the Task has already been canceled, a call to the listener will be immediately scheduled. If multiple listeners are added, they will be called in the order in which they were added.
     *
     * @param executor the executor to use to call the listener
     * @return this Task
     */
    public Task<TResult> addOnCanceledListener(Executor executor, OnCanceledListener listener) {
        throw new UnsupportedOperationException("addOnCanceledListener is not implemented");
    }

    /**
     * Adds an Activity-scoped listener that is called if the Task is canceled.
     * <p>
     * The listener will be called on main application thread. If the Task has already been canceled, a call to the listener will be immediately scheduled. If multiple listeners are added, they will be called in the order in which they were added.

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