第一次自动登录

Question

我正在创建聊天应用程序，并在其中添加了Firebase的注册/登录功能，但是每当我从Firebase控制台中清除所有数据和注册用户并从我的设备中卸载该应用程序并从头开始重新安装时，它就会直接运行进入主要活动（意味着用户可以在注册/登录后进入），而不是询问注册/登录（这是开始活动）。怎么样？

MainActivity.java

package com.jimmytrivedi.lapitchat;

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

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

public class MainActivity extends AppCompatActivity {

    private FirebaseAuth mAuth;
    private FirebaseUser currentUser;
    private Toolbar toolbar;
    private ViewPager viewPager;
    private SectionsPagerAdapter sectionsPagerAdapter;
    private TabLayout tabLayout;
    private DatabaseReference UserDatabaseReference;

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

        mAuth = FirebaseAuth.getInstance();
        viewPager = findViewById(R.id.viewPager);
        sectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        viewPager.setAdapter(sectionsPagerAdapter);

        toolbar = findViewById(R.id.mainToolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("Home");

        tabLayout = findViewById(R.id.tabLayout);
        tabLayout.setupWithViewPager(viewPager);

        currentUser = mAuth.getCurrentUser();

    }

    @Override
    public void onStart() {
        super.onStart();
        if (currentUser == null) {
            sendTostart();
        } else {
            UserDatabaseReference = FirebaseDatabase.getInstance().getReference().child("Users").child(mAuth.getCurrentUser().getUid());
            UserDatabaseReference.child("Online").setValue(true);
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (currentUser != null) {
            UserDatabaseReference.child("Online").setValue(false);
        }
    }

    private void sendTostart() {
        startActivity(new Intent(MainActivity.this, StartActivity.class));
        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.logout) {
            FirebaseAuth.getInstance().signOut();
            sendTostart();
        }

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

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

        return true;
    }
}

StartActivity.java

package com.jimmytrivedi.lapitchat;

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

public class StartActivity extends AppCompatActivity {

    private Button signup, exist;

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

        signup = findViewById(R.id.signup);
        exist = findViewById(R.id.exist);

        signup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(StartActivity.this,RegisterActivity.class));
            }
        });

        exist.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(StartActivity.this,LoginActivity.class));
            }
        });
    }
}

更新的代码，但仍然存在相同的问题：

MainActivity.java

package com.jimmytrivedi.lapitchat;

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

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

public class MainActivity extends AppCompatActivity {

    private FirebaseAuth mAuth;
    private FirebaseUser currentUser;
    private Toolbar toolbar;
    private ViewPager viewPager;
    private SectionsPagerAdapter sectionsPagerAdapter;
    private TabLayout tabLayout;
    private DatabaseReference UserDatabaseReference;

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

        mAuth = FirebaseAuth.getInstance();
        viewPager = findViewById(R.id.viewPager);
        sectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        viewPager.setAdapter(sectionsPagerAdapter);

        toolbar = findViewById(R.id.mainToolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("Home");

        tabLayout = findViewById(R.id.tabLayout);
        tabLayout.setupWithViewPager(viewPager);

        currentUser = mAuth.getCurrentUser();

        if (currentUser == null) {
            sendTostart();
        } else {
            UserDatabaseReference = FirebaseDatabase.getInstance().getReference().child("Users").child(mAuth.getCurrentUser().getUid());
            UserDatabaseReference.child("Online").setValue(true);
        }

    }

    @Override
    protected void onPause() {
        super.onPause();
        if (currentUser != null) {
            UserDatabaseReference.child("Online").setValue(false);
        }
    }

    private void sendTostart() {
        startActivity(new Intent(MainActivity.this, StartActivity.class));
        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.logout) {
            FirebaseAuth.getInstance().signOut();
            sendTostart();
        }

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

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

        return true;
    }
}