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.

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.

View on GitHub (pinned to 157c9d86ac)

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.