[Android]Workerの複数起動を防ぐ

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:orientation="vertical">

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:text="Worker Start"/>

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:text="Worker Stop"/>
    </LinearLayout>

</RelativeLayout>

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    //定数
    final private static String LOG_TAG = "worker_sample";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button1 = findViewById(R.id.button1);
        button1.setOnClickListener(this);
        Button button2 = findViewById(R.id.button2);
        button2.setOnClickListener(this);
    }


    /* Workerを起動 */
    private void startWrok (int num) {
        //Wrokerが稼働中かチェック
        //  稼働中なら終了
        WorkManager manager = WorkManager.getInstance(this);
        if (isWorkerEnqueued(manager,SampleWorker.WORK_TAG)) {
            Log.d(LOG_TAG, "Worker already enqueued");
            return;
        }

        //Workerに渡すデータを作成
        Data data =  new Data.Builder()
                .putInt("num", num)
                .build();

        //制約（起動条件）を設定
        //　　このサンプルでは制約なしでもいいが
        //　　とりあえずバッテリー容量が少ないときはNGとした
        Constraints constraints = new Constraints.Builder()
                .setRequiresBatteryNotLow(true)
                .build();

        //WorkRequestの作成
        // PeriodicWorkRequestを使って20分毎に定期実行
        PeriodicWorkRequest request = new PeriodicWorkRequest.Builder(
                SampleWorker.class, 20, TimeUnit.MINUTES)
                .setConstraints(constraints)
                .setInputData(data)
                .addTag(SampleWorker.WORK_TAG)
                .build();

        //キューに登録（スケジューリング）
        manager.enqueue(request);

        UUID uuid = request.getId();
        ListenableFuture<WorkInfo> future = manager.getWorkInfoById(uuid);

        Log.d(LOG_TAG, "Worker scheduled");

    }

    /* Workerを停止 */
    private void stopWork() {
        WorkManager manager = WorkManager.getInstance(this);
        manager.cancelAllWorkByTag(SampleWorker.WORK_TAG);
        Log.d(LOG_TAG, "Worker stopped");
    }

    /* ---------------------------------------------
        Workerの状態を取得する
        引数：workManager = WorKManagerのインスタンス
            tag = タグ
        戻値：true = 稼働中
            false = 非稼働
    ----------------------------------------------- */
    private boolean isWorkerEnqueued(WorkManager workManager, String tag) {
        ListenableFuture<List<WorkInfo>> future =  workManager.getWorkInfosByTag(tag);
        try {
            for (WorkInfo workInfo : future.get()){
                //workInfoからstateを取得して状態をチェック
                if (workInfo.getState() != WorkInfo.State.CANCELLED) {
                    //CANCELLED以外だったら稼働中とみなす
                    return true;
                };
            }
        } catch (ExecutionException | InterruptedException e) {
            e.printStackTrace();
            return false;
        }
        return false;
    }


    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button1:
                startWrok(2);   //Workerを起動
                break;
            case R.id.button2:
                stopWork();     //Workerのキャンセル
                break;
            default:
                break;
        }
    }
}

public class SampleWorker extends Worker {
    //定数
    final private static String LOG_TAG = "worker_sample";
    final public static String WORK_TAG = "SampleWorkerTAG";

    //コンストラクタ
    public SampleWorker(@NonNull Context context, @NonNull WorkerParameters workerParams) {
        super(context, workerParams);
    }

    @NonNull
    @Override
    public Result doWork() {
        //データを取得
        Data data = getInputData();
        int num = data.getInt("num", 1);

        //出力テキストの作成
        //numの個数だけ"Beautiful"というテキストを出力
        StringBuilder sb = new StringBuilder();
        for (int i=0; i<num; i++) {
            sb.append("Beautiful ");
        }
        sb.append(getId().toString());
        String output = sb.toString().trim();

        //出力
        Log.d(LOG_TAG,output);  //ログに出力
        return Result.success();
    }
}