Android: showing an alertdialog while internet is not connected in device

I want to check if the internet is connected and show a dialog if it is not. This is my code:

network_class.java

 public class network_class {
    public static boolean isConnectedToInternet(Context context){
        ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        if (activeNetwork != null) {
            if (activeNetwork.getType() == ConnectivityManager.TYPE_WIFI) {
                return true;
            }
            else if(activeNetwork.getType() == ConnectivityManager.TYPE_MOBILE) {
                return true;
            }
        }
        return false;
    }
}

network_detector.java

public class network_detector extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        View alertdialog_1 = LayoutInflater.from(context).inflate(R.layout.network_dialog,null);
        AlertDialog.Builder dialog_1 = new AlertDialog.Builder(context);
        dialog_1.setView(alertdialog_1);

        AlertDialog dialog = dialog_1.create();
        dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

        dialog.setCancelable(false);
        if(network_class.isConnectedToInternet(context)){
            if(dialog.isShowing())
                dialog.cancel();
        }
        else
            dialog.show();
    }
}

After that, I am using the receiver in my MainActivity:

network_detector detector = new network_detector();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //some irrelevant code here
}

@Override
protected void onStart() {
    IntentFilter intentFilter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
    registerReceiver(detector,intentFilter);
    super.onStart();
}

@Override
protected void onStop() {
    unregisterReceiver(detector);
    super.onStop();
}

While the application is running in my device, when I switch off the internet the dialog shows (which is correct), and then again when I switch on the internet, strangely enough the dialog still keeps on showing. Why is that? Where am I going wrong?

EDIT: These permissions are there in my manifest:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />

>Solution :

It doesn’t dismiss because you are creating a different AlertDialog every time you get on the onReceive so you should store a variable in the NetworkDetector class.

public class network_detector extends BroadcastReceiver {

    private AlertDialog dialog;

    @Override
    public void onReceive(Context context, Intent intent) {
         if (dialog != null) {
            boolean isConnected = networkClass.isConnectedToInternet(context);
            if (isConnected) {
                dialog.dismiss();
                dialog = null;
            } else if (!dialog.isShowing()) {
                showNoInternetDialog(context);
            }
        } else {
            showNoInternetDialog(context);
        }

}


    private void showNoInternetDialog(Context context) {
        View alertdialogView = LayoutInflater.from(context).inflate(R.layout.network_dialog, null);
        AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(context);
        dialogBuilder.setView(alertdialogView);

        dialog = dialogBuilder.create();
        dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

        dialog.setCancelable(false);
        dialog.show();
    }
}