Android Oreo上小部件的屏幕开/关广播侦听器

Question

我有一个时钟小部件Android应用程序，我现在正试图更新到API 26的要求。

到目前为止，我使用了一个后台服务，它在启动时在其onCreate方法aBroadcastReceiver中注册，以接收系统广播，例如android。意图行动屏幕打开，Android。意图行动关掉屏幕，Android。意图行动时间到了，Android。意图行动时区已更改。然后，这项服务在屏幕关闭时暂停时钟，在屏幕重新打开时唤醒时钟，以节省电池。

在Oreo中，这类服务似乎不是一个选项，因为它必须在前台运行，并带有一个对用户没有意义的通知。此外，据我在文档中看到的，JobScheduler也帮不上我的忙，因为我没有发现可以将作业安排到屏幕打开时。

我尝试在AppWidgetProvider类中创建一个BroadcastRecencer，并将其注册到AppWidgetProvider的onUpdate方法中以接收所述系统广播。这工作得很好，广播确实被接收到，但仅在屏幕关闭一段时间后；之后，应用程序似乎以某种方式被系统杀死，或者以其他方式停止工作而没有任何报告的错误或崩溃；但是如果我单击它，它会像往常一样打开配置活动。

我的问题是：

>

如果我不想运行前台服务，如何正确收听API 26上的屏幕开/关广播？

是否可以收听来自AppWidgetProvider类本身的系统广播，方法是在其中注册BroadcastRecencer，或者甚至注册AppWidgetProvider本身来接收系统事件（无论如何AppWidgetProvider是BroadcastRecencer的扩展）。

为什么我的AppWidgetProvider在一段睡眠时间后会突然停止接收广播的系统意图？

编辑：

我在Android留档中找到了以下内容，这似乎是我的问题2和3的答案。

注意：不能从BroadcastReceiver组件调用此方法；也就是说，来自应用程序清单中声明的BroadcastReceiver。但是，从另一个在运行时已向registerReceiver（BroadcastReceiver，IntentFilter）注册的BroadcastReceiver调用此方法是可以的，因为这样一个注册的BroadcastReceiver的生存期与注册它的对象相关联。

我的结论是，我在AppWidgetProvider中使用和注册BroadcastRecencer违反了本规范。

我将保留这篇文章，因为其他人可能会发现这些信息很有用，我的问题1仍然有效。

Answer 1

下面是我在Android API 26（Oreo）及以上版本中收听SCREEN_OFF和SCREEN_ON广播的步骤。这个答案与widget无关，但找到一些解决方法可能会有所帮助。

我正在使用作业调度器来注册和注销广播接收器，它可以监听屏幕关闭和屏幕打开操作。

import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Build;
import android.os.PowerManager;
import android.support.annotation.NonNull;
import android.util.Log;

import com.evernote.android.job.Job;
import com.evernote.android.job.JobManager;
import com.evernote.android.job.JobRequest;

import java.util.concurrent.TimeUnit;


public class LockScreenJob extends Job {

    private static final String TAG = LockScreenJob.class.getSimpleName();

    public static final String TAG_P = "periodic_job_tag";
    public static final String TAG_I = "immediate_job_tag";

    //Used static refrence of broadcast receiver for ensuring if it's already register or not NULL
    // then first unregister it and set to null before registering it again.
    public static UnlockReceiver aks_Receiver = null;

    @Override
    @NonNull
    protected Result onRunJob(Params params) {
        // run your job here

        String jobTag = params.getTag();

        if (BuildConfig.DEBUG) {
            Log.i(TAG, "Job started! " + jobTag);
        }

        PowerManager pm = (PowerManager) getContext().getSystemService(Context.POWER_SERVICE);

        boolean isInteractive = false;
        // Here we check current status of device screen, If it's Interactive then device screen is ON.
        if (Build.VERSION.SDK_INT >= 20) {
            isInteractive = pm.isInteractive();
        } else {
            isInteractive = pm.isScreenOn();
        }

        try {
            if (aks_Receiver != null) {
                getContext().getApplicationContext().unregisterReceiver(aks_Receiver); //Use 'Application Context'.
            }
        } catch (Exception e) {
            if (BuildConfig.DEBUG) {
                e.printStackTrace();
            }
        } finally {
            aks_Receiver = null;
        }

        try {
            //Register receiver for listen "SCREEN_OFF" and "SCREEN_ON" action.

            IntentFilter filter = new IntentFilter("android.intent.action.SCREEN_OFF");
            filter.addAction("android.intent.action.SCREEN_ON");
            aks_Receiver = new UnlockReceiver();
            getContext().getApplicationContext().registerReceiver(aks_Receiver, filter); //use 'Application context' for listen brodcast in background while app is not running, otherwise it may throw an exception.
        } catch (Exception e) {
            if (BuildConfig.DEBUG) {
                e.printStackTrace();
            }
        }

        if (isInteractive)
        {
          //TODO:: Can perform required action based on current status of screen.
        }

        return Result.SUCCESS;
    }

    /**
     * scheduleJobPeriodic: Added a periodic Job scheduler which run on every 15 minute and register receiver if it's unregister. So by this hack broadcast receiver registered for almost every time w.o. running any foreground/ background service. 
     * @return
     */
    public static int scheduleJobPeriodic() {
        int jobId = new JobRequest.Builder(TAG_P)
                .setPeriodic(TimeUnit.MINUTES.toMillis(15), TimeUnit.MINUTES.toMillis(5))
                .setRequiredNetworkType(JobRequest.NetworkType.ANY)
                .build()
                .schedule();

        return jobId;
    }

    /**
     * runJobImmediately: run job scheduler immediately so that broadcasr receiver also register immediately
     * @return
     */
    public static int runJobImmediately() {
        int jobId = new JobRequest.Builder(TAG_I)
                .startNow()
                .build()
                .schedule();

        return jobId;
    }

    /**
     * cancelJob: used for cancel any running job by their jobId.
     * @param jobId
     */
    public static void cancelJob(int jobId) {
        JobManager.instance().cancel(jobId);
    }
}

我的JobCrator类LockScreenJobCreator是：

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import com.evernote.android.job.Job;
import com.evernote.android.job.JobCreator;

public class LockScreenJobCreator implements JobCreator {

    @Override
    @Nullable
    public Job create(@NonNull String tag) {
        switch (tag) {
            case LockScreenJob.TAG_I:
                return new LockScreenJob();
            case LockScreenJob.TAG_P:
                return new LockScreenJob();
            default:
                return null;
        }
    }
}

BroadcastRecencer类UnlockRecencer是：

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.util.Log;

public class UnlockReceiver extends BroadcastReceiver {

    private static final String TAG = UnlockReceiver.class.getSimpleName();

    @Override
    public void onReceive(Context appContext, Intent intent) {

        if (BuildConfig.DEBUG) {
            Log.i(TAG, "onReceive: " + intent.getAction());
        }

        if (intent.getAction().equalsIgnoreCase(Intent.ACTION_SCREEN_OFF))
        {
          //TODO:: perform action for SCREEN_OFF
        } else if (intent.getAction().equalsIgnoreCase(Intent.ACTION_SCREEN_ON)) {
          //TODO:: perform action for SCREEN_ON
        }
    }

}

将JobCreator类添加到应用程序类中，如下所示：

public class AksApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();

       JobManager.create(this).addJobCreator(new LockScreenJobCreator());   

       //TODO: remaing code
    }

}

别忘了在AndroidManifest中定义应用程序类。xml

所有这些之后，我从我的活动中启动作业调度器，如下所示：

import android.support.v7.app.AppCompatActivity;

public class LockScreenActivity extends AppCompatActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        runJobScheduler();

        //TODO: other code
    }

    @Override
    protected void onStop() {
      super.onStop();

      cancelImmediateJobScheduler();

      //TODO: other code
    }

    /**
     * runJobScheduler(): start immidiate job scheduler and pending job schedulaer from 
       your main Activity.
     */
    private void runJobScheduler() {
        Set<JobRequest> jobSets_I = null, jobSets_P = null;
        try {
            jobSets_I = JobManager.instance().getAllJobRequestsForTag(LockScreenJob.TAG_I);
            jobSets_P = JobManager.instance().getAllJobRequestsForTag(LockScreenJob.TAG_P);

            if (jobSets_I == null || jobSets_I.isEmpty()) {
                LockScreenJob.runJobImmediately();
            }
            if (jobSets_P == null || jobSets_P.isEmpty()) {
                LockScreenJob.scheduleJobPeriodic();
            }

            //Cancel pending job scheduler if mutiple instance are running.
            if (jobSets_P != null && jobSets_P.size() > 2) {
                JobManager.instance().cancelAllForTag(LockScreenJob.TAG_P);
            }
        } catch (Exception e) {
            if (Global_Var.isdebug) {
                e.printStackTrace();
            }
        } finally {
            if (jobSets_I != null) {
                jobSets_I.clear();
            }
            if (jobSets_P != null) {
                jobSets_P.clear();
            }
            jobSets_I = jobSets_P = null;
        }
    }


    /**
     * cancelImmediateJobScheduler: cancel all instance of running job scheduler by their 
      TAG name. 
     */
    private void cancelImmediateJobScheduler() {  
            JobManager.instance().cancelAllForTag(LockScreenJob.TAG_I);
    }
}

通过运行这样的作业调度程序，我可以在不运行任何前台或后台服务的情况下，监听屏幕关闭和屏幕打开操作。我在API 26上测试了上述代码，它运行良好。