Android Studio - Autenticacion Con Firebase 1/3

MainActivity.class

  private static final String TAG = "Antut" ;
    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private EditText mEmailField,mPasswordField;
    private Button mLoginBtn;

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

        mAuth = FirebaseAuth.getInstance();

        mEmailField = (EditText) findViewById(R.id.email);
        mPasswordField = (EditText) findViewById(R.id.password);
        mLoginBtn = (Button) findViewById(R.id.login);

        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {

                if(firebaseAuth.getCurrentUser()!=null){

                    startActivity(new Intent(MainActivity.this,SegundaActivity.class));
                   
                }
                else {
                   // Toast.makeText(MainActivity.this, "Datos Incorrectos", Toast.LENGTH_SHORT).show();

                }
            }
        };

        mLoginBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
             LoginUsuario();
            }
        });




    }

    @Override
    protected void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(mAuthListener);
    }



    private void LoginUsuario(){


       String email = mEmailField.getText().toString();
        String password = mPasswordField.getText().toString();

        mAuth.signInWithEmailAndPassword(email, password)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        Log.d(TAG, "signInWithEmail:onComplete:" + task.isSuccessful());

                        // If sign in fails, display a message to the user. If sign in succeeds
                        // the auth state listener will be notified and logic to handle the
                        // signed in user can be handled in the listener.
                        if (!task.isSuccessful()) {
                            Log.w(TAG, "signInWithEmail", task.getException());
                            Toast.makeText(MainActivity.this, "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                        }

                        // ...
                    }
                });
             }




}

Android Studio - Notificaciones

MainActivity.class

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.app.NotificationCompat;
import android.view.View;
import android.widget.Button;


public class MainActivity extends AppCompatActivity {

    private Button boton;
    NotificationCompat.Builder notificacion;
    private static final int idUnica = 51623;

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


        boton = (Button) findViewById(R.id.boton);

        notificacion = new NotificationCompat.Builder(this);
        notificacion.setAutoCancel(true);


        boton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                notificacion.setSmallIcon(R.mipmap.ic_launcher);
                notificacion.setTicker("Nueva notificacion");
                notificacion.setPriority(Notification.PRIORITY_HIGH);
                notificacion.setWhen(System.currentTimeMillis());
                notificacion.setContentTitle("Titulo");
                notificacion.setContentText("Tutorial Antut Notificaciones");

                Intent intent = new Intent(MainActivity.this,MainActivity.class);

                PendingIntent pendingIntent = PendingIntent.getActivity(MainActivity.this,0,intent,PendingIntent.FLAG_UPDATE_CURRENT);
                notificacion.setContentIntent(pendingIntent);


                NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
                nm.notify(idUnica,notificacion.build());

            }
        });



    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.usuario.videotest.MainActivity">


  <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Notificacion"
      android:id="@+id/boton"
      android:layout_centerInParent="true"/>

</RelativeLayout>