A utility class to keep track if your app is in the foreground or background

ApplicationWatcher.kt

package com.pantos27.hamburgersforbreakfast

import android.app.Activity
import android.os.Bundle
/**
 *   A utility class to keep track if your app is in the foreground or background
 *   without any special permission or API restrictions
 *   Note that if your app has any activities that run on a different 
 *   process (through the process attribute in your manifest) this utility might not be persistent 
 *    
 */
object ApplicationWatcher : android.app.Application.ActivityLifecycleCallbacks {
    private var started : Int? = null
    private var resumed : Int? = null
    interface StateChangedListener{
        fun onForeground()
        fun onBackground()
    }

    var listener: StateChangedListener? = null

    override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) {
    }

    override fun onActivityStarted(activity: Activity) {
        started ?: listener?.onForeground()

        started = activity.hashCode()
    }

    override fun onActivityResumed(activity: Activity) {
        started ?: listener?.onForeground()

        started = activity.hashCode()
        resumed = activity.hashCode()
    }

    override fun onActivityPaused(activity: Activity) {
        if (resumed==activity.hashCode()){
            resumed=null
        }
    }

    override fun onActivityStopped(activity: Activity) {
        if (started==activity.hashCode()){
            started=null
            listener?.onBackground()

        }
    }

    override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle?) {
    }

    override fun onActivityDestroyed(activity: Activity) {
    }

    public fun isAppStarted() = started!=null
    public fun isAppResumed() = resumed!=null
}

MyApplication.java

package com.pantos27.hamburgersforbreakfast

public class MyApplication extends android.app.Application {
  
    @Override
    public void onCreate() {
        super.onCreate();
        //register watcher
        registerActivityLifecycleCallbacks(ApplicationWatcher.INSTANCE);
        
        ApplicationWatcher.INSTANCE.setListener(new ApplicationWatcher.StateChangedListener() {
				  @Override
				  public void onForeground() {
              //you're on!
				  }

				  @Override
				  public void onBackground() {
              //you're off!
				  }
			  });


    }


    @Override
    public void onTerminate() {
        super.onTerminate();
        //unregister watcher
        unregisterActivityLifecycleCallbacks(ApplicationWatcher.INSTANCE);
    }
}

hi can you convert this utility ApplicationWatcher.kt only to a java, because am using react native and i want to use this code in android source code

You can use Kotlin in react native

The recommended way to do this is to use ProcessLifecycleOwner