How does a Android “OS” detect a incoming call

Question

I\'d like to know:

1. how the android OS detect a incoming call(number) and displays the contact name and gives us a option to attend the call.
2. What happ

Answer 1

In Android it is possible to detect call events using the built-in TelephonyManager API.TelephonyManager class provides access to information about the telephony services on the device.

Example :

Create a new class called MyCallReceiver

package com.example;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.telephony.TelephonyManager;
import android.widget.Toast;

public class MyCallReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

        if (intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(TelephonyManager.EXTRA_STATE_RINGING)) {
            // This code will execute when the phone has an incoming call

            // get the phone number 
            String incomingNumber = intent.getStringExtra(TelephonyManager.EXTRA_INCOMING_NUMBER);
            Toast.makeText(context, "Call from:" +incomingNumber, Toast.LENGTH_LONG).show();

        } else if (intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(
                TelephonyManager.EXTRA_STATE_IDLE)
                || intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(
                        TelephonyManager.EXTRA_STATE_OFFHOOK)) {
            // This code will execute when the call is disconnected
            Toast.makeText(context, "Detected call hangup event", Toast.LENGTH_LONG).show();

        }
    }
}

BroadcastReceiver class that will monitor the phone state and whenever there is a change in phone state, the onReceive() method of the BroadcastReceiver will be called.

Add the READ_PHONE_STATE permission in your AndroidManifest.xml

Check this for references : BroadcastReceiver