main_java_com_example_harsh_freechat_MainActivity.java

package com.example.harsh.freechat;

import android.content.Intent;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toolbar;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ServerValue;

public class MainActivity extends AppCompatActivity {

    private FirebaseAuth mAuth;
    private android.support.v7.widget.Toolbar mToolbar;
    private ViewPager mViewPager;
    private SectionsPagerAdapter mSectionsPagerAdapter;
    private DatabaseReference mUserRef;
    private TabLayout mTablayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mAuth = FirebaseAuth.getInstance();
        mToolbar=findViewById(R.id.main_page_toolbar);
        setSupportActionBar(mToolbar);
        getSupportActionBar().setTitle("Free Chat");
        if(mAuth.getCurrentUser()!=null) {
            mUserRef = FirebaseDatabase.getInstance().getReference().child("Users").child(mAuth.getCurrentUser().getUid());
        }
        mViewPager=findViewById(R.id.main_tabPager);
        mSectionsPagerAdapter= new SectionsPagerAdapter(getSupportFragmentManager());
        mViewPager.setAdapter(mSectionsPagerAdapter);
        mTablayout=findViewById(R.id.main_tabs);
        mTablayout.setupWithViewPager(mViewPager);


    }
    @Override
    public void onStart() {
        super.onStart();
        // Check if user is signed in (non-null) and update UI accordingly.
        FirebaseUser currentUser = mAuth.getCurrentUser();
        if (currentUser == null) {
            sendtoStart();
        } else{
            mUserRef.child("online").setValue("true");
    }

    }

    protected void onStop() {
        super.onStop();
        FirebaseUser currentUser = mAuth.getCurrentUser();
        if (currentUser!=null) {
            mUserRef.child("online").setValue(ServerValue.TIMESTAMP);


        }
    }


    private void sendtoStart() {
        Intent startIntent=new Intent(MainActivity.this,StartActivity.class);
        startActivity(startIntent);
        finish();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
         super.onCreateOptionsMenu(menu);

         getMenuInflater().inflate(R.menu.main_menu,menu);


         return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
         super.onOptionsItemSelected(item);
         if(item.getItemId()==R.id.main_logout_btn){
             FirebaseAuth.getInstance().signOut();
             sendtoStart();

         }

         if(item.getItemId()==R.id.main_settings_btn){
             Intent settingsintent=new Intent(MainActivity.this,SettingsActivity.class);
             startActivity(settingsintent);


         }

         if(item.getItemId()==R.id.main_all_btn)
         {
             Intent settingsintent=new Intent(MainActivity.this,UsersActivity.class);
             startActivity(settingsintent);
         }
         return true;
    }
}