Inconvertible types; cannot cast android.app.Application error?

Question

My goal is to detect when the user goes into the background. I used this answer to get me setup

However when I replace where there is "MyApplication" in his code, with my classname ("MainActivity"). I can the inconvertible types error.

I'm new to android studio and do not know how to go about fixing this. Any and help is appreciated.

Main Activity Code:

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {



    private Timer mActivityTransitionTimer;
    private TimerTask mActivityTransitionTimerTask;
    public boolean wasInBackground;
    private final long MAX_ACTIVITY_TRANSITION_TIME_MS = 2000;

    @Override
    public void onResume()
    {
        super.onResume();

        MainActivity myApp = (MainActivity)this.getApplication();
        if (myApp.wasInBackground)
        {
            //Do specific came-here-from-background code
        }

        myApp.stopActivityTransitionTimer();
    }

    @Override
    public void onPause()
    {
        super.onPause();
        ((MainActivity)this.getApplication()).startActivityTransitionTimer();
    }

   public void startActivityTransitionTimer() {
        this.mActivityTransitionTimer = new Timer();
        this.mActivityTransitionTimerTask = new TimerTask() {
            public void run() {
                MainActivity.this.wasInBackground = true;
            }
        };

        this.mActivityTransitionTimer.schedule(mActivityTransitionTimerTask,
                MAX_ACTIVITY_TRANSITION_TIME_MS);
    }

    public void stopActivityTransitionTimer() {
        if (this.mActivityTransitionTimerTask != null) {
            this.mActivityTransitionTimerTask.cancel();
        }

        if (this.mActivityTransitionTimer != null) {
            this.mActivityTransitionTimer.cancel();
        }

        this.wasInBackground = false;
    }

}

Location of error

EDIT: AndroidManifest.xml below:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.jstudios.cars">


    <application
        android:name=".MyApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="Cars"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".SplashActivity"
            android:label="@string/app_name"
            android:theme="@style/SplashTheme">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".MainActivity"
            android:configChanges="orientation|keyboardHidden"
            android:label="CarsApp"
            android:screenOrientation="portrait"
            android:theme="@style/AppTheme.NoActionBar"></activity>
    </application>

</manifest>

Intent filter is for the splash screen.

EDIT: @Modi Harsh

LifeCycleObserverClassCode:

Directories Of LifeCycleObserver:

Input of Code in MainActivity:

EDIT 2 ERROR IN MainActivityJava:

EDIT 2 ERROR IN MyLifeCycleObserverClass:

Answer 1

You need to create a class which extends Application - this is not the same as your Main activity. The docs describe it as:

Base class for maintaining global application state. You can provide your own implementation by creating a subclass and specifying the fully-qualified name of this subclass as the "android:name" attribute in your AndroidManifest.xml's tag. The Application class, or your subclass of the Application class, is instantiated before any other class when the process for your application/package is created.

It will look like this:

public class MyApplication extends Application {

}

Inside your Manifest.xml file you will need something like this to tell Android about your custom application class:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      package="your.package.name">

....

    <application
           android:name=".MyApplication"
           android:icon="@mipmap/ic_launcher"
           android:label="@string/app_name"
           android:roundIcon="@mipmap/ic_launcher_round"
           android:supportsRtl="true">
</manifest>

I think you need to move your startActivityTransitionTimer and stopActivityTransitionTimer methods to your new MyApplication class.

Then your onPause and onResume methods should be able to use this:

(MyApplication) this.getApplication()

PS you can call your MyApplication class anything you want.

PPS it might be worth reading about the fundamentals of Android components here

Answer 2

It can be achieved through Android Architecture Component: LifeCycle

Add in build.gradle

implementation 'android.arch.lifecycle:extensions:1.1.1'

Create your Observer class and implements with LifecycleObserver

Kotlin :

class MyLifeCycleObserver : LifecycleObserver {

private var lifeCycleObserverCallback: LifeCycleObserverCallback? = null

    fun registerCallback(lifeCycleObserverCallback: LifeCycleObserverCallback) {
        this.lifeCycleObserverCallback = lifeCycleObserverCallback
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    private fun onAppForeground() {
        lifeCycleObserverCallback?.onForeground()
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    private fun onAppBackground() {
        lifeCycleObserverCallback?.onBackground()
    }

    public interface LifeCycleObserverCallback {
        fun onForeground()
        fun onBackground()
    }
}

Java :

public class MyLifeCycleObserver implements LifecycleObserver {

    private LifeCycleObserverCallback lifeCycleObserverCallback;

    public void registerCallback(LifeCycleObserverCallback lifeCycleObserverCallback) {
        this.lifeCycleObserverCallback = lifeCycleObserverCallback;
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    private void onAppForeground() {
        lifeCycleObserverCallback.onForeground();
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    private void onAppBackground() {
        lifeCycleObserverCallback.onBackground();
    }

    public interface LifeCycleObserverCallback{
        void onForeground();
        void onBackground();
    }
}

Add this few lines in your Activity in onCreate

Kotlin :

val observer = MyLifeCycleObserver()
lifecycle.addObserver(observer)
observer.registerCallback(this)

Java :

MyLifeCycleObserver observer = new MyLifeCycleObserver();
getLifecycle().addObserver(observer);
observer.registerCallback(this);

After that implements LifeCycleObserverCallback listener in your Activity and override both methods

Kotlin :

override fun onForeground() {
//    do whatever you want (App in Foreground)
}

override fun onBackground() {
//    do whatever you want (App in Background)
}

Java :

@Override
public void onForeground() {
//    do whatever you want (App in Foreground)
}

@Override
public void onBackground() {
//    do whatever you want (App in Background)
}

And done :)