Develop Reference

Is it possible to lock the complete device from a flutter app?

I want to lock my android device as soon as a particular event happens in an application. The application will keep running in the background and lock the device as soon as the event happens. I tried plugins like flutter_screen_lock but they only provide locking within the particular app while I want the complete device to get locked.

Quick answer to your question this is not possible. If it would be possible both App Distribution Providers (App- and Play Store) would not accept your App because it would be against those Rules.

How can I put a lock on my app so It can't be removed from recent screens

I want to put a lock icon to my app. How can I do that programmatically as in some social apps like in the following picture? I want to prevent the user from clearing my app from recent screens or task as it's using services in the background and Oppo, Mi and Lenovo kills it. I already tried it but it didn't work for me
startLockTask();

Firstly, that lock is not implemented by Whatsapp or any other social networking site. That lock is set by the user manually.
And what does that Lock do is whenever the user clears RAM, then all the applications that are locked will not be killed if that (app) is either in the foreground or background. So that's nothing to do with the code of that particular app.
Now, quoting this line: I want user to prevent from clearing my app from recent screens.
Users can still clear any of the locked apps manually. That means if they swipe any locked app, then that app will be cleared. That lock only prevents the clearing of app when the user taps on clear RAM.
All in all, You can't set that kind of lock programmatically in any of your apps.

Are android apps still running in background if I am getting notifications?

Here is the thing, I am not used to the latest android yet and the new system is giving me some confusions. Usually, for the older androids, if I close all background apps, I won't get new notifications from them. But after switching to a new phone with the latest android, I realized that even if I do close all background apps, I still keep getting notifications from them. So, how are the apps still pushing notifications if I already close them from background?
(Say google maps for example, I am 100% sure I killed it in background but now it keeps notifies me about my live traffic status on my notification bar.)

So Here's the answer-
Yes, they are. Whenever the Internet is turned on or you get a message, listener of that app wakes up and check for any notification and if there is something new, it shows you the notification.
These apps keep running in the background if not put in sleep mode by your phone and use the resources.
Like you don't want to get notified by WhatsApp for a new message but the moment you change the network, unlock your phone again or turn the data on, an event listener will wake up and notify you of new messages.
Also, wake timers are used to notify you after some fixed time like after every 5 minutes.
This is the thing I hate the most.
Not promoting but here's the app - search play store for Shutapp - Real battery saver (Blocked from Play store a while ago and doesn't work anymore for "obvious" reasons). It will turn off all the background apps and you'll be amazed to see a long list on first use.
This will remove all the apps from background until you open them again. I use this app most of the time and it really works great.
Try this out.

Sticky Service and Intent Service gets killed when the app is destroyed

In My app I am trying to download images even though user has force stopped it and exit it using recent app manager by swiping . Why I want this behavior, it has only one reason and that is :
Because I want User to stop the download from my button given in activity
So For this I have made async task at first place , it was working nicely even the activity is destroyed, But When I destroy/kill my app using recent app manger the app gets killed and so the service
Then I moved my async task to the Service which is Sticky , I thought it should not get destroy when the user closes the app from recent app lists, but The service stops. though some times it start again , but due to some reason I just want it to not to stop and download like a google play store does. What ever you do , you can not stop downloading of app , until and unless you use stop button in the google play store app.
Then I read about IntentService, about intent service I read that ,
You can run intent service and forget about it , as it stops itself
after completion of task.
So I though this is something , which could not be killed even user stops it or close app from recent app list by swiping , as intent service would perform its task and would stop itself
But All in vein. I have read many things about the service and how to cure service from being not killed. I came to know about starting service as forground.
But what other ways do other Top class apps adopt to keep the background working all the time , like security apps , gps based apps, and antivirus apps whose services run all the time on background. You can examine same behaviour inn google play store app , you can start downloading of any app and exit the play store app , even from recent app tray , but it would continue to download until and unless you go to notification bar click notification , get navigated to place where you finally see stop downloading button to stop downloading the app.
So How can I achieve this ? what is wrong with service or what else can I use to get the same behavior as google play store has.
Please guide me . Your comments and discussion would be appreciated.

It sounds like you want to run your service in a separate process from your main application so it does not get killed if the app is removed from the "Recent Tasks" list.
This is made possible by using the "Process" attribute explained in the documentation here:
http://developer.android.com/guide/topics/manifest/service-element.html#proc

What you need is a ForegroundService. The android developer guide about services states that:
A foreground service is a service that's considered to be something the user is actively aware of and thus not a candidate for the system to kill when low on memory. A foreground service must provide a notification for the status bar, which is placed under the "Ongoing" heading, which means that the notification cannot be dismissed unless the service is either stopped or removed from the foreground.

You can use return return START_STICKY in onStartCommand in service

How to prevent android app from updating from the google play store?

I have an android app that is published in the Google Play Store. The Google Play Store app is how end-users install updates. I realize it's up to the user's discretion to turn on auto-updates, so this feature may or may not be turned on with any given phone.
My app runs a foreground service with an icon in the notification bar when it's running. During testing of the auto-update procedure, I noticed that if the service is running and the app updates itself, the service is shutdown (which is to be expected since new code is being installed).
However, I would like to avoid this if at all possible. What I would like to happen is find a way to detect when auto-update tries to update my app. If the service is running, I'd like to deny updates until the service finishes it's work and shuts down.
So is there any way to detect when the google play store attempts to update your app, and if so, is there a way to block the update until you determine your app is in a safe state to shutdown?

Unfortunately, I don't think there is a way to detect when the Play Store attempts to update your app, unless you have a second app to listen for this event. And even if you have a way to detect this, I don't think you can cancel the update.
Maybe it would be an idea for you to transfer the work you are doing to your second app while the first one is being updated. However, I needn't say that this sounds like a very hacky solution.
You should focus on saving your state and continuing from where you left after the application is updated and started.