Develop Reference

Create an incoming call screen on Android

I'm looking for a way to show the default "incoming call screen" to the user.
The user should be able to interact it (i.e. answer/deny) and my application should receive this chosen action.
Although I can design my own "incoming call screen" for sure (kind of faking the default one), but is there any way to ask Android (on a physical device) to display the default screen (I would populate the phone number / name to display).
I don't want to create this screen from scratch, as it won't be exact with the system default, and it would take quite some time for me.
(Motivation: I'm customizing an Android phone, it will show an incoming call screen when the call is actually coming into my other phone - two phones will negotiate the notification/actions via some common interface like Bluetooth or Wifi).
ps: rooting is available, so I have literally no limitation.

How can I launch a Samsung home screen shortcut via Tasker?

My security company's mobile app (CPI inTouch) allows me to create "scenes" which trigger multiple actions at the same time with a press of one button (e.g. disarming the alarm and unlocking the smart lock on my door). I've also added shortcuts to each of the scenes on my home screen (on my Samsung Galaxy Note9, if that's relevant) so I can launch a scene via the shortcut without having to go into the app itself.
However, having just purchased Tasker, I'd like to trigger the shortcut (or the activity in the app itself) programmatically in a Tasker profile or some other automation app. I've tried plenty of apps that allow you to trigger a shortcut based on an event, but none have these particular shortcuts in the list of available ones. I read that I should be able to use a Send Intent task in Tasker to do this, but I don't know what the intent string would be or where to find it.
In case you can suggest a different way to achieve this, the main use case so far is to have my alarm system automatically disarmed when my phone's morning alarm goes off.

First thing to check would be...
create new task to Launch App,
find your CPI app and if it has a "+" in top right corner of app icon you can long press it to reveal a list of activities.
if your app does not offer those options...
The Tasker dev also has a group of plugins under the AutoApps group, there is one called AutoShortcut that launches shortcuts.
edit: there are apps such as APK Analyzer that can show you the activities and services inside an app and whether or not they can receive intents from external apps.

scroll android programmatically in all applications

I created a background service on android and I have two buttons which appear on the top of the screen all the time. I want to use these two buttons like scroll down and scroll up. But these two buttons should work on any kind of applications like Instagram, Facebook, Twitter and so. So, it means it should work in all applications that use scrolling.
I search a week on internet but I could not find any solutions.

This is not possible, sorry. Something like this would require your Service to have access to the Views of the applications and this would be a huge security breach, because you could read values from them and so on.
You could achieve this with a custom button code broadcast (so basically your buttons would act as physical buttons on the device) but this would most probably require you to have system-level permissions and some level of cooperation with the OEMs.
Android Activity class has a method called dispatchKeyEvent(), which could let you simulate the key input (with some limitations) but this is not present in the Service class.

Sadly this is not something you can do in Android. Typically you should not be able to touch views with a background service, the point of a background service is that you do some work in it (for example upload files to your web server or get some data). You CAN send a signal from a service once you're finished doing work to tell an app that something needs to happen, however the app needs to be specifically coded to respond to this broadcasted event.
If you wanted to do this with an app that you have developed, that can be achieved by using the onReceive method of say a BroadcastReceiver, however you cannot specifically define the behaviour of other apps as this would represent a security breach in Android.

How to use volume keys to open a activity when device is locked?

Hi all i want make app which run over volume key for example when we press the volume down key it turn camera open( when device is locked) similarly i want the same in my app.

I don't think that's possible
Those functionalities come from the factory OS you have, not from specific apps. The only way that could be possible is by rooting the device, in which case you may be able to listen to physical button clicks and modify their behaviour.
This page shows an application that can alter the buttons behaviour once the device is rooted, but again, this won't teach you how to do it, as again, it's not for the majority of the users and you'd need to root every device.

Use default incoming call screen fro making fake call

Is there a way to use default incoming call screen with its functionality (answer and reject) from inside my application.
I want to make fake call from inside my application and i don't want to create custom incoming screen but use default incoming call screen on device because different devices have different incoming screens.

No, this can't be done using the standard SDK. First, the call screen activity can only be launched by the system. Second, vendor-specific skins of Android often replace the default phone app with a custom one, so it's unlikely you'd be able to do this on all devices with just a single piece of code even if it were possible.
Your best bet would be to try to recreate the incoming call screen for the most popular devices and detect which device the user is running, which I know isn't what you wanted to hear. Sorry.