ActivityLifecycleMonitor.java
/*
* 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;
import android.app.Activity;
import java.util.Collection;
/**
* Interface for tests to use when they need to query the activity lifecycle state.
*
* <p>Activity lifecycle changes occur only on the UI thread - therefore listeners registered with
* an ActivityLifecycleMonitor should expect to be invoked on the UI thread. The direct query
* methods can only be called on the UI thread because otherwise they would not be able to return
* consistent responses.
*
* <p>Retrieve instances of the monitor through {@link ActivityLifecycleMonitorRegistry}.
*
* <p>Detecting these lifecycle states requires support from Instrumentation, therefore do not
* expect an instance to be present under any arbitrary instrumentation.
*/
public interface ActivityLifecycleMonitor {
/**
* 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 are 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 ActivityLifecycleCallback
*/
void addLifecycleCallback(ActivityLifecycleCallback callback);
/** Removes a previously registered lifecycle callback. */
void removeLifecycleCallback(ActivityLifecycleCallback callback);
/**
* Returns the current lifecycle stage of a given activity.
*
* <p>This method can only return a consistent and correct answer from the main thread, therefore
* callers should always invoke it from the main thread and implementors are free to throw an
* exception if the call is not made on the main thread.
*
* <p>Implementors should ensure this method returns a consistent response if called from a
* lifecycle callback also registered with this monitor (eg: it would be horriblely wrong if a
* callback sees PAUSED and calls this method with the same activity and gets RESUMED.
*
* @param activity an activity in this application.
* @return the lifecycle stage this activity is in.
* @throws IllegalArgumentException if activity is unknown to the monitor.
* @throws NullPointerException if activity is null.
* @throws IllegalStateException if called off the main thread.
*/
Stage getLifecycleStageOf(Activity activity);
/**
* Returns all activities in a given stage of their lifecycle.
*
* <p>This method can only return a consistant and correct answer from the main thread, therefore
* callers should always invoke it from the main thread and implementors are free to throw an
* exception if the call is not made on the main thread.
*
* <p>Implementors should ensure this method returns a consistant response if called from a
* lifecycle callback also registered with this monitor (eg: it would be horriblely wrong if a
* callback sees PAUSED and calls this method with the PAUSED and does not see its activity in the
* response.
*
* <p>Callers should be aware that the monitor implementation may not hold strong references to
* the Activities in the application. Therefore stages which are considered end stages or eligible
* for garbage collection on low memory situations may not return an instance of a particular
* activity if it has been garbage collected.
*
* @param stage the stage to query for.
* @return a snapshot Collection of activities in the given stage. This collection may be empty.
* @throws IllegalStateException if called from outside the main thread.
*/
Collection<Activity> getActivitiesInStage(Stage stage);
}