LifecycleObserver which allows easy cancelling of coroutines

CoroutineLifecycleObserver.kt

/*
 * Copyright 2018 Google LLC
 *
 * 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.
 */

class CoroutineLifecycleObserver : LifecycleObserver {
    var job: Job = Job()
        private set
    
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun start() {
        // If the job is complete (happens after being previously stopped)
        // lets create a new one
        if (job.isCompleted) {
            job = Job()
        }
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun cancel() {
        // If the job is active (running) cancel it
        if (job.isActive) {
            job.cancel()
        }
    }
}

class DetailFragment : Fragment() {
    private val coroutineLifecycle = CoroutineLifecycleObserver()
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // Add observer so any jobs are automatically cancelled
        lifecycle.addObserver(coroutineLifecycle)
    }
    
    private fun runTask() {
        // Set the coroutine parent from LifecycleObserver so that it will
        // be automatically cancelled in onStop
        launch(parent = coroutineLifecycle.job) { 
            // do something long-running
        }
      
        launch(parent = coroutineLifecycle.job) { 
            // do something else long-running
        }
        
        // both of these will be cancelled in onStop (if still running)
    }
}