Android jetpack（Workmanager）篇

Workmanager是jetpack系列及其重要的一部分，他可以让用户设定定时任务，并设定一些条件，条件符合并到达时间后会自动执行，他的兼容性极高，在API23以上，它采用JobScheduler，以下采用AlarmManage和广播接受者。Workmanager他不是神，他也有延迟，他是系统提供出来的，很多app都能共享，所以同一时间的任务多，那么就会造成排队等候，就有了延迟。所以Workmanager适用于不急着使用的后台定时任务，如果像要下载文件等及时更新的，那么就还是service适合。

使用

设置Worker：

public class MyWork extends Worker {
    public MyWork(@NonNull Context context, @NonNull WorkerParameters workerParams) {
        super(context, workerParams);
    }

    @NonNull
    @Override
    public Result doWork() {
        SystemClock.sleep(2000);
        Log.d("yanjin","doWork了！！！！");
        return Result.success();
    }
}

然后开始调用

WorkManager workManager = WorkManager.getInstance(WorkerManagerActivity.this);
workManager.enqueue(workRequest);

那么就需要一个workRequest，这里我们设置一个一次性任务

OneTimeWorkRequest workRequest = new OneTimeWorkRequest.Builder(MyWork.class)
                .setConstraints(constraints)
                .build();

至此我们可以调用了，但是如果我们要加限制，那么就要额外添加如下代码：

Constraints constraints = new Constraints.Builder()
                .setRequiredNetworkType(NetworkType.NOT_REQUIRED)//设置网络情况
                .setRequiresBatteryNotLow(true)//设置在电量不足的情况下不执行
                .setRequiresCharging(true)//在充电时执行
                .setRequiresStorageNotLow(true)//设置在容量不足的情况下不执行
//                .setRequiresDeviceIdle(true)//在待机情况下执行，需要判断api大于23
                .build();

全部代码如下：

public class WorkerManagerActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_worker_manager);
        findViewById(R.id.tv_one_time).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                oneTime();
            }
        });
    }

    /**
     * 一次性任务
     */
    private void oneTime() {
        Constraints constraints = new Constraints.Builder()
                .setRequiredNetworkType(NetworkType.NOT_REQUIRED)//设置网络情况
                .setRequiresBatteryNotLow(true)//设置在电量不足的情况下不执行
                .setRequiresCharging(true)//在充电时执行
                .setRequiresStorageNotLow(true)//设置在容量不足的情况下不执行
//                .setRequiresDeviceIdle(true)//在待机情况下执行，需要判断api大于23
                .build();
        OneTimeWorkRequest workRequest = new OneTimeWorkRequest.Builder(MyWork.class)
                .setConstraints(constraints)
                .setInitialDelay(1000, TimeUnit.MILLISECONDS)//延时一秒
                .build();
        WorkManager workManager = WorkManager.getInstance(WorkerManagerActivity.this);
        workManager.enqueue(workRequest);
    }
}

退避策略

如果我们doWork里面返回的是Result.retry();那么我们很可能需要重试，比如我们上一次的任务因为没有网络导致没有执行，那么我们就要重试，并且我们还需要设置重试的时间间隔怎么办？那么就用到这个退避策略了。如下：

OneTimeWorkRequest workRequest = new OneTimeWorkRequest.Builder(MyWork.class)
                .setConstraints(constraints)
                .setInitialDelay(1000, TimeUnit.MILLISECONDS)//延时一秒
                .setBackoffCriteria(BackoffPolicy.LINEAR, Duration.ofSeconds(2))//线性增长，如果失败首先隔两秒再次请求，如果再次失败就是4秒
                .build();

BackoffPolicy还有EXPONENTIAL，指数型增长，可以自由试试。

获取任务状态以及取消任务

workManager.getWorkInfoByIdLiveData(workRequest.getId()).observe(this, new Observer() {
            @Override
            public void onChanged(WorkInfo workInfo) {
                Log.d("yanjin","workInfo state = "+workInfo.getState());
            }
        });

通过监听id就能获取到任务的状态，并且也可以取消任务。

workManager.cancelWorkById(workInfo.getId());

数据的传递

workRequest中可以添加data数据源

Data data = new Data.Builder()
                .putString(KEY,"input")
                .build();
        OneTimeWorkRequest workRequest = new OneTimeWorkRequest.Builder(MyWork.class)
                .setConstraints(constraints)
                .setInitialDelay(1000, TimeUnit.MILLISECONDS)//延时一秒
                .setBackoffCriteria(BackoffPolicy.LINEAR, Duration.ofSeconds(2))//线性增长，如果失败首先隔两秒再次请求，如果再次失败就是4秒
                .addTag(TAG)
                .setInputData(data)
                .build();

在doWork中获取

@NonNull
    @Override
    public Result doWork() {
        Data inputData = getInputData();
        String name = inputData.getString(WorkerManagerActivity.KEY);
        Log.d("yanjin","输出的数据 = "+name);
        SystemClock.sleep(2000);

        Data data = new Data.Builder()
                .putString(WorkerManagerActivity.KEY,"input")
                .build();
        return Result.success(data);
    }

当然我们看到Result.success(data)，同样我们也可以把处理的结果返回。在监听任务状态中获取

workManager.getWorkInfoByIdLiveData(workRequest.getId()).observe(this, new Observer() {
            @Override
            public void onChanged(WorkInfo workInfo) {
                if(workInfo != null && workInfo.getState() == WorkInfo.State.SUCCEEDED){
                    Data data = workInfo.getOutputData();
                    String name = data.getString(KEY);
                    Log.d("yanjin","传出的数据 = "+name);
                }

            }
        });

这样，一个轮回就完成了。

周期性任务

PeriodicWorkRequest是设置周期性执行任务的对象，大部分设置和OneTimeWorkRequest一样但是注意，他的最小周期是15分钟！！！

任务链以及任务组合

OneTimeWorkRequest workRequest1 = new OneTimeWorkRequest.Builder(MyWork.class)
                .build();
        OneTimeWorkRequest workRequest2 = new OneTimeWorkRequest.Builder(MyWork.class)
                .build();
        final WorkManager workManager = WorkManager.getInstance(WorkerManager2Activity.this);
        workManager.beginWith(workRequest1).then(workRequest2).enqueue();

这是简单的任务链，先执行1再执行2。那么如果我们想要如下需求呢？

image.png

OneTimeWorkRequest workRequestA = new OneTimeWorkRequest.Builder(MyWork.class)
                .build();
        OneTimeWorkRequest workRequestB = new OneTimeWorkRequest.Builder(MyWork.class)
                .build();
        OneTimeWorkRequest workRequestC = new OneTimeWorkRequest.Builder(MyWork.class)
                .build();
        OneTimeWorkRequest workRequestD = new OneTimeWorkRequest.Builder(MyWork.class)
                .build();
        OneTimeWorkRequest workRequestE = new OneTimeWorkRequest.Builder(MyWork.class)
                .build();
        WorkContinuation ABContinuation = WorkManager.getInstance(WorkerManager2Activity.this).beginWith(workRequestA).then(workRequestB);
        WorkContinuation CDContinuation = WorkManager.getInstance(WorkerManager2Activity.this).beginWith(workRequestC).then(workRequestD);
//这里需要变成集合
        List continuations = new ArrayList<>();
        continuations.add(ABContinuation);
        continuations.add(CDContinuation);
        WorkContinuation.combine(continuations).then(workRequestE).enqueue();