Push Notification in Andriod

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="OneSignal Notification"
        android:textSize="40sp"
        android:textStyle="bold"
        android:gravity="center"
        android:layout_margin="16dp"/>

</RelativeLayout>

MainActivity.java

package trusof.com.onesignaldemo;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import com.onesignal.OneSignal;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        //Onesignal initialization
        OneSignal.startInit(this)
                .inFocusDisplaying(OneSignal.OSInFocusDisplayOption.Notification)
                .unsubscribeWhenNotificationsAreDisabled(true)
                .init();
    }
}

google-services.json

{
  "project_info": {
    "project_number": "859844779565",
    "project_id": "onesignal-42b00",
    "storage_bucket": "onesignal-42b00.appspot.com"
  },
  "client": [
    {
      "client_info": {
        "mobilesdk_app_id": "1:859844779565:android:1add1f48153bcb6a0be2a4",
        "android_client_info": {
          "package_name": "trusof.com.onesignaldemo"
        }
      },
      "oauth_client": [
        {
          "client_id": "859844779565-8lbpj7671t4ap14i6ildjq2dhph2t5do.apps.googleusercontent.com",
          "client_type": 3
        }
      ],
      "api_key": [
        {
          "current_key": "AIzaSyDufwJEfLJEk5Yg5o5eU7lQDd4u2RgW81E"
        }
      ],
      "services": {
        "appinvite_service": {
          "other_platform_oauth_client": [
            {
              "client_id": "859844779565-8lbpj7671t4ap14i6ildjq2dhph2t5do.apps.googleusercontent.com",
              "client_type": 3
            }
          ]
        }
      }
    }
  ],
  "configuration_version": "1"
}

build.gradle (OneSignalDemo)

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath "com.android.tools.build:gradle:4.1.3"
        classpath 'com.google.gms:google-services:4.3.10'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

build.gradle (:app)

buildscript {
    repositories {
        maven { url 'https://plugins.gradle.org/m2/'}
    }
    dependencies {
        classpath 'gradle.plugin.com.onesignal:onesignal-gradle-plugin:0.12.9'
    }
}
apply plugin: 'com.onesignal.androidsdk.onesignal-gradle-plugin'

repositories {
    maven { url 'https://maven.google.com' }
}
apply plugin: 'com.android.application'


android {
    compileSdkVersion 31

    defaultConfig {
        applicationId "trusof.com.onesignaldemo"
        minSdkVersion 16
        targetSdkVersion 31
        versionCode 3
        versionName "3.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    android {
        defaultConfig {
            manifestPlaceholders = [
                    onesignal_app_id: '7c2eef73-7293-4b19-9cd0-dc6eaa734139',
                    onesignal_google_project_number: 'REMOTE'
            ]
        }
    }

}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.0'
    implementation 'com.onesignal:OneSignal:3.15.3'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}
apply plugin: 'com.google.gms.google-services'