MyService.class

public class MyService extends Service {
    public MyService() {
    }

    //  创建一个服务
    @Override
    public void onCreate() {
        super.onCreate();
    }
    //    服务启动
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.i("MyServer", "服务启动了");
        Timer timer = new Timer();

        int n = 5 * 60 * 10000;
        timer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {

                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        Looper.prepare();
                        // TODO: 2019/11/7
                        AlertDialog.Builder builder=new AlertDialog.Builder(MyApp.getContext());
                        builder.setTitle("提示");
                        builder.setMessage("已经过去五分钟了\n且行器珍惜");
                        builder.setNegativeButton("明白了",null);
                        Dialog dialog=builder.create();
                        dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
                        dialog.show();
                        Looper.loop();
                    }
                }).start();
                Log.i("MyServer","五分钟了");
            }
        }, 10000, n);

        return super.onStartCommand(intent, flags, startId);
    }

    //    服务销毁
    @Override
    public void onDestroy() {
        stopSelf();
        super.onDestroy();
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        return new MyBinder();
    }
    class MyBinder extends Binder {
        /**
         * 获取Service的方法 * @return 返回PlayerService
         */
        public MyService getService() {
            return MyService.this;
        }
    }

}

注意 Looper.prepare()和 Looper.loop()这两行，少了它们会报Can't create handler inside thread that has not called Looper.prepare()这个错误

在AndroidManifest中

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/><!--这行代码必须存在，否则点击不了系统设置中的按钮-->
    <uses-permission android:name="android.permission.SYSTEM_OVERLAY_WINDOW" />

不过服务一般在创建的时候它就会自己帮我们添加了

<service
            android:name=".MyService"
            android:enabled="true"
            android:exported="true"></service>

在Activity中绑定服务

public class MainActivity extends AppCompatActivity {

    public Intent intent;
    ServiceConnection serviceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
//            建立连接
//            获取服务操作对象
            MyService.MyBinder binder = (MyService.MyBinder) service;
            binder.getService();//获取到Service
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intent = new Intent(this, MyService.class);
        startService(intent);//启动服务
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
//        stopService(intent);
//        程序销毁时，退出服务
    }

}