Develop Reference

How to block user from changing to other apps

I want to make an activity in my native android app that doesn't allow to change to other apps, or open settings or go back to home screen, just like the alarm apps do when the alarm comes in, but I can't find anything about how to do this.
Does anybody know how to do this?

What abilities does being the default "Assist" app give to an app?

I need to know what can I do with my app if the user changes my app to default assist app.
I'd like to know what abilities this role grants, preferably with the source of the information.

I know that this will make your application start when 3 things happen:
When the user long-clicks the home button in the navigation bar
When the user presses the assistant button on their Device ( if their device has it )
when an another application starts the assist app ( your app ) using this code: startActivity(new Intent("android.intent.action.VOICE_COMMAND"));

How to make a phone call without switching activities to a default calling app in android?

I'm trying to make a phone call from my app in a way it does not need to switch activities, But every guide I find has the following code snippet,
Intent callIntent = new Intent(Intent.ACTION_CALL);
callIntent.setData(Uri.parse("tel:XXXXXXXXX"));
startActivity(callIntent);
which switches the activity I start the call from to another activity (in this case to an activity in a different app). Is there a way to stop this from happening? I managed to do it with a third party library called "sinch" but I'm wondering if there is a native way to do it or maybe a better library?
Ps- the app I'm building it for myself, basically, I'm building a voice assistant that can make calls via voice commands, hence I can't let it switch activities. I have no intention of publishing it on the app store and I have no difficulty giving dangerous permissions :) My plan is to run it on a separate piece of hardware in the future.

This link can help you, but as Xavier Rubio Jansana wrote previously, Google hardly accepts applications that do not use intents to make phone calls :
https://google-developer-training.github.io/android-developer-phone-sms-course/Lesson%201/1_c_phone_calls.html
Google wants any programmer to use an intent to make the user view the default phone application handle the phone call.
If your app does not need to be available on Google Play Store then it would be ok for you to make the phone call directly.

To elaborate on what I was talking about earlier, it is talked about in this stack overflow question (perhaps upvote their answers if they are helpful). How to make a phone call using intent in Android?.
From memory, ACTION_DIAL will bring up the dialler and pre-populate the number.. it requires no special permission because it requires the user to actually place the call.
On the other hand, ACTION_CALL will actually initiate the call and requires special permissions.
If returning focus (bringing your app back to the foreground) is a concern, you could try using a scheduled intent to (re) launch your activity (maybe using alarm manager or similar) some time after invoking the dialler. You can retain state with a little care around launch modes in the intent and/or a special "do nothing" activity published in your app manifest which does nothing but re-activate your app.

Clear other apps data programmatically?

I am developing an android application and i need clear the data of another application upon clicking an button.
i.e.: if i click button name "gmail" in my app,the data should be cleared of that "gmail" app
doubt:
1.Is it possible?
2.Do we need to be rooted our android device in order to do this?
° because greenify works with root access to force stop the other app flexibly.
I know that greenify works without root but pop that "force stop" ui screen of each single app to do that action.
MY APP FUNCTIONALITY:
I just wanted to develop an android apllication named "anti-theft cloud apps"
simply if an thief stols our mobile then my app detects when he changes the sim or an unique code send by mobile owner through sms from other mobile and logouts all the cloud based applications like gmail,google photos etc to protect our data to be stolen ,so in order to do that i thought of clearing other apps data(like gmail) PROGTAMITICALLY to logout. Is it possible

This is not possible with stock Android. You can do it with superuser, access root/data/data/PACKAGE and clear its content. But as seen in comment, this seems like evil thing.

How to launch my app programmatically, if an another app opens?

I want my app automatically open when user click (for example) chrome or any other apps.
How to do this?
My app is for preventing people use cell phone all the time.
Explicitly, there is a mission in my app. when user starts this mission, user cannot use other app until they give up the mission.
User can minimize my app, but when user click another app, my app will prompt programmatically to tell user not to use the cell phone.

Instead of preventing user to launch other apps, I think you should use activities' life cycle. You can add code in onPause() and detect user press home button or back button. And when your activity is not on foreground, you can pop a dialog or something to remind your user focus on his work not his phone. BTW I do see the positive side of your app.