六、WorkManager 后台线程
WorkManager 用于 App 中不需要及时完成的任务（如上报日志、同步数据），因为将任务落盘到数据库故其保证即使设备重启、App 彻底退出，都依然会执行，其省电，兼容几乎所有设备（高版本用 JobScheduler，低版本用 AlarmManager，最终都是用 Adnroid 的 Executor 执行的），架构如下图。
首先，新建项目，项目github地址详见，在 build.gradle(app) 添加如下依赖：
def work_version = "2.7.1"
implementation "androidx.work:work-runtime-ktx:$work_version"
然后，新建UploadLogWorker 类，负责上报日志，代码如下：
package com.bignerdranch.android.jetpack6workmanagertest
import android.content.Context
import android.util.Log
import androidx.work.Data
import androidx.work.Worker
import androidx.work.WorkerParameters
// 上传日志的Worker
class UploadLogWorker(context: Context, workerParams: WorkerParameters) : Worker(context, workerParams) {
/**
* 耗时的任务，在doWork()方法中执行
*
* 执行成功返回Result.success()
* 执行失败返回Result.failure()
* 需要重新执行返回Result.retry()
*/
override fun doWork(): Result {
//接收外面传递进来的数据
val inputData: String? = inputData.getString("input_data")
Log.e("UploadLogWorker", "doWork()->get inputData:$inputData")
// 任务执行完成后返回数据
val outputData: Data = Data.Builder().putString("output_data", "Task Success!").build()
return Result.success(outputData)
}
}
新建 CompressLogWorker，表示任务成功运行，代码如下：
class CompressLogWorker(context: Context, workerParams: WorkerParameters) : Worker(context, workerParams) {
/**
* 耗时的任务，在doWork()方法中执行
*
* 执行成功返回Result.success()
* 执行失败返回Result.failure()
* 需要重新执行返回Result.retry()
*/
override fun doWork(): Result {
Log.e("CompressLogWorker", "doWork()")
return Result.success()
}
}
6.1 用 WorkRequest 配置任务的运行时机、方式
- 设置任务触发条件
例如当设备充电、已联网、电量充足时，触发任务，代码如下：
val constraints: Constraints = Constraints.Builder()
.setRequiresCharging(true)
.setRequiredNetworkType(NetworkType.CONNECTED)
.setRequiresBatteryNotLow(true)
.build()
- 将任务触发条件、延迟执行，指数退避策略、标签，设置到 WorkRequest
val uploadWorkRequest = OneTimeWorkRequest.Builder(UploadLogWorker::class.java)
.setConstraints(constraints)//设置触发条件
.setInitialDelay(10, TimeUnit.SECONDS) // 符合触发条件后，延迟10秒执行
.setBackoffCriteria(BackoffPolicy.LINEAR, OneTimeWorkRequest.MIN_BACKOFF_MILLIS, TimeUnit.MILLISECONDS) //设置指数退避算法
.setInputData(inputData)
.addTag("UploadTag")
.build()
通过 WorkManager.getWorkInfosByTag() 可得到 WorkInfo 对象，通过 WorkManager.getWorkInfosByTagLiveData() 可监听任务状态变化，通过 cancelAllWork() 可取消所有任务，
6.2 一次性、周期性、任务链的 Work
完整的 MainActivity 代码如下：
package com.bignerdranch.android.jetpack6workmanagertest
import android.os.Bundle
import android.util.Log
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.work.*
import java.util.concurrent.TimeUnit
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
startOneTimeTask()
// startPeriodicWorkRequest();
// startChainTask();
}
// 开启一个一次性任务
private fun startOneTimeTask() {
val constraints: Constraints = Constraints.Builder()
.setRequiresCharging(true)
.setRequiredNetworkType(NetworkType.CONNECTED)
.setRequiresBatteryNotLow(true)
.build()
val inputData: Data = Data.Builder().putString("input_data", "Hello World!").build()
val uploadWorkRequest = OneTimeWorkRequest.Builder(UploadLogWorker::class.java)
.setConstraints(constraints)//设置触发条件
.setInitialDelay(10, TimeUnit.SECONDS) // 符合触发条件后，延迟10秒执行
.setBackoffCriteria(BackoffPolicy.LINEAR, OneTimeWorkRequest.MIN_BACKOFF_MILLIS, TimeUnit.MILLISECONDS) //设置指数退避算法
.setInputData(inputData)
.addTag("UploadTag")
.build()
WorkManager.getInstance(this).enqueue(uploadWorkRequest)
//实时监听变化
WorkManager.getInstance(this).getWorkInfoByIdLiveData(uploadWorkRequest.id).observe(this@MainActivity) {
workInfo ->
Log.d("onChanged()->", "workInfo:$workInfo")
if (workInfo != null && workInfo.state == WorkInfo.State.SUCCEEDED) {
val outputData = workInfo.outputData.getString("output_data")
Log.d("onChanged()->", "doWork()->get outputData:$outputData")
Toast.makeText(this@MainActivity, "Success!", Toast.LENGTH_LONG).show()
}
}
}
private val TAG = "PeriodicTask"
/**
* 开启一个定期任务
*
* 通过设置TAG的方式来监听任务状态的变化，也可以使用ID的方式来监听
*/
private fun startPeriodicWorkRequest() {
val constraints: Constraints = Constraints.Builder()
.setRequiresCharging(true)
.build()
//不能少于15分钟
val uploadWorkRequest = PeriodicWorkRequest.Builder(UploadLogWorker::class.java, 15, TimeUnit.MINUTES)
.setConstraints(constraints) //设置触发条件
.addTag(TAG)
.build()
WorkManager.getInstance(this).enqueue(uploadWorkRequest)
WorkManager.getInstance(this).getWorkInfosByTagLiveData(TAG)
.observe(this@MainActivity) {
workInfos -> Log.d("onChanged()->", "workInfo:" + workInfos!![0]) }
}
/**
* 取消任务
*/
private fun cancelAllWork() {
WorkManager.getInstance(this@MainActivity).cancelAllWork()
}
/**
* 开启任务链，任务的执行具有先后顺序
*/
private fun startChainTask() {
val constraints: Constraints = Constraints.Builder()
.setRequiresCharging(true)
.build()
val compressWorkRequest = OneTimeWorkRequest.Builder(CompressLogWorker::class.java)
.setConstraints(constraints) //设置触发条件
.setInitialDelay(10, TimeUnit.SECONDS) //符合触发条件后，延迟10秒执行
.build()
val uploadWorkRequest = OneTimeWorkRequest.Builder(UploadLogWorker::class.java)
.setConstraints(constraints) //设置触发条件
.setInitialDelay(10, TimeUnit.SECONDS) //符合触发条件后，延迟10秒执行
.build()
//实时监听变化
WorkManager.getInstance(this).getWorkInfoByIdLiveData(uploadWorkRequest.id)
.observe(this@MainActivity) {
workInfo -> Log.d("onChanged()->", "workInfo:$workInfo") }
}
}
运行后，打印日志如下，说明监听到了任务状态的变化：
2022-09-28 15:54:48.643 11533-11533/com.bignerdranch.android.jetpack6workmanagertest D/onChanged()->: workInfo:WorkInfo{
mId='34e59f1e-3bd7-4ec7-9d4c-974dd314e1a9', mState=ENQUEUED, mOutputData=Data {
}, mTags=[com.bignerdranch.android.jetpack6workmanagertest.UploadLogWorker, UploadTag], mProgress=Data {
}}