/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package androidx.test.runner.lifecycle;

/**
 * Interface for tests to use when they need to be informed of the application lifecycle state.
 *
 * <p>Retrieve instances of the monitor thru ApplicationLifecycleMonitorRegistry.
 *
 * <p>Detecting these lifecycle states requires support from Instrumentation, therefore do not
 * expect an instance to be present under any arbitrary instrumentation.
 */
public interface ApplicationLifecycleMonitor {

  /**
   * Adds a new callback that will be notified when lifecycle changes occur.
   *
   * <p>Implementors will not hold a strong ref to the callback, the code which registers callbacks
   * is responsible for this. Code which registers callbacks should responsibly remove their
   * callback when it is no longer needed.
   *
   * <p>Callbacks may be executed on the main thread of the application, and should take care not to
   * block or otherwise perform expensive operations as it will directly impact the application.
   *
   * @param callback an ApplicationLifecycleCallback
   */
  void addLifecycleCallback(ApplicationLifecycleCallback callback);

  /** Removes a previously registered lifecycle callback. */
  void removeLifecycleCallback(ApplicationLifecycleCallback callback);
}