public class ApplicationListener implements Application.ActivityLifecycleCallbacks {

    private int foregroundCount = 0; 

    @Override
    public void onActivityStarted(Activity activity) {
        if (foregroundCount <= 0) {
            // TODO becomes foreground
        }
        foregroundCount++;
    }

    @Override
    public void onActivityStopped(Activity activity) {
        foregroundCount--;
        if (foregroundCount <= 0) {
            // TODO goes background
        }
    }

    /*
     * The following callbacks, we do not need
     */

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {}

    @Override
    public void onActivityResumed(Activity activity) {}

    @Override
    public void onActivityPaused(Activity activity) {}

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {}

    @Override
    public void onActivityDestroyed(Activity activity) {}

}

That is.

If ActivityA go to ActivityB，the callbacks is :

A.onPause()
B.onStart()
B.onResume()
A.onStop()

If ActivityB return ActivityA, the callbacks is:

B.onPause()
A.onStart()
A.onResume()
B.onStop()

So, set a counter to statistics onStart() and onStop() callbacks. if the counter is > 0, Application is in foreground, opposite in background.

I tried to use the gradle dependency as: compile 'com.sjl:Foredroid:1.0.1' This package doesn't exist in jcenter or maven-central. Per this page: https://bintray.com/steveliles/maven/Foredroid/1.0.1?versionPath=%2Fsteveliles%2Fmaven%2FForedroid%2F1.0.1

The package that is available is: compile 'Foredroid:Foredroid:unspecified'

Can you publish 1.0.2 version that fixes these problems? Thanks.

In the weak references to call backs, when iterating over the CopyOnWriteArrayList and the weak reference is pointing to a null, remove() is called on the iterator, which is not allowed and throws an illegal operation exception, which is buried and the item is never removed. Removal has to happen after iteration is complete.

Hi there. I got a memory leak ( from Canary Leak ) coming from Foreground.current I'm only doing this Foreground.get(application).addListener(foregroundListener) in onCreate and unbinding in onDestroy. Any ideas?

• The leak occurred whenever the current activity was backgrounded, no new activity was started, and the activity was then destroyed (e.g. switching to another app with DKA enabled). This has been resolved by replacing the current Activity strong reference with a currentActivity weak reference

Resolves issue #8

Hi @steveliles, thank you for this helpful class. But i get the error: "Cannot resolve method: removeListener(com.sjl.foreground.Foreground.Listener)" Can fix this please?

Thank you

the old code when it going to "it.remove();",there is a exception ,"java.lang.UnsupportedOperationException" . The CopyOnWriteArrayList doc describe is “Iterators returned by this list and its sub lists cannot modify the

• underlying list. In particular, {@link Iterator#remove}, {@link
• ListIterator#add} and {@link ListIterator#set} all throw {@link
• UnsupportedOperationException}.”. It doesn't impliment "remove" method.

This is my solution: private List<WeakReference> listeners = new ArrayList<>();

Please check this issues ,thank you very much for offering so good tool.

it was a quick implementation to Observe app state using RxJava event bus. hope this could help to support an Rx way for who is already using RxJava and RxAndroid.

the onBecameForeground calls multiple times if you have more than one activity on stack, so if you have three activities on stack, the onBecameForeground calls thrice. how to fix that.

Implemented same as in sample app. onBecameForeground called onBecameBackground never called. At the time of going background listeners becomes empty (due to weak reference) and thus hasn't been called

Looks like the delayed check in onActivityPaused() is the reason.

Foreground thinks it is the background, altough it is in the foreground. Thus onBecameForeground() gets called when the started activity has finshed.

Only happens if I put the app in the background two times or more.

When I request permission, App became Background.

package com.sjl.foreground.demo;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import com.sjl.foreground.Foreground;

import java.util.ArrayList;
import java.util.List;

public abstract class DemoActivity extends ActionBarActivity implements Foreground.Listener {

    private Foreground.Binding listenerBinding;

    protected abstract void startAnotherActivity();

    public static final int REQUEST_ID_MULTIPLE_PERMISSIONS = 1;


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

        Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //startAnotherActivity();
                //composeEmail(new String[]{"asdasd"},"asdas");
                ActivityCompat.requestPermissions(DemoActivity.this,
                        new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                        1);
            }
        });

        listenerBinding = Foreground.get(getApplication()).addListener(this);
    }

    public void composeEmail(String[] addresses, String subject) {
        Intent intent = new Intent(Intent.ACTION_SENDTO);
        intent.setData(Uri.parse("mailto:")); // only email apps should handle this
        intent.putExtra(Intent.EXTRA_EMAIL, addresses);
        intent.putExtra(Intent.EXTRA_SUBJECT, subject);
        if (intent.resolveActivity(getPackageManager()) != null) {
            startActivity(intent);
        }
    }

    private  boolean checkAndRequestPermissions() {
        int permissionSendMessage = ContextCompat.checkSelfPermission(this,
                Manifest.permission.SEND_SMS);
        int locationPermission = ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION);
        List<String> listPermissionsNeeded = new ArrayList<>();
        if (locationPermission != PackageManager.PERMISSION_GRANTED) {
            listPermissionsNeeded.add(Manifest.permission.ACCESS_FINE_LOCATION);
        }
        if (permissionSendMessage != PackageManager.PERMISSION_GRANTED) {
            listPermissionsNeeded.add(Manifest.permission.SEND_SMS);
        }
        if (!listPermissionsNeeded.isEmpty()) {
            ActivityCompat.requestPermissions(this, listPermissionsNeeded.toArray(new String[listPermissionsNeeded.size()]),REQUEST_ID_MULTIPLE_PERMISSIONS);
            return false;
        }
        return true;
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();

        // not strictly necessary as Foreground only holds a weak reference
        // to the listener to defensively prevent leaks, but its always better
        // to be explicit and WR's play monkey with the Garbage Collector
        listenerBinding.unbind();
    }

    @Override
    public void onBecameForeground() {
        Log.d(Foreground.TAG, getClass().getName() + " became foreground");
    }

    @Override
    public void onBecameBackground() {
        Log.d(Foreground.TAG, getClass().getName() + " went background");
    }

}

everything works fine until you open a dialog, when the dialog is showing the status of activity change to "background" , when the dialog is closed don't update the status . . .