应用程序在打开时崩溃而没有显示错误

Question

在手机（j5）和模拟器（nexus 5）上同时打开应用程序后，我的应用程序就会崩溃。我把它提供给其他人尝试在他的计算机上运行，​​他说它确实可以打开，因此我不确定问题的根源是什么，我也没有发现错误（logcat中的红线很少，但我没有知道如何使用它...） 我是一个初学者，我使用Youtube教程（https://www.youtube.com/watch?v=9qcJk9DA4Sg）以此为基础构建应用程序。到目前为止，我只关注了第一部分，但是在视频结尾时，它似乎可以在他的设备上运行...

我不知道代码或设备是否有问题，所以这是代码。

主要活动

package com.example.myapp;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

import com.google.firebase.auth.FirebaseAuth;

public class MainActivity extends AppCompatActivity {

    private FirebaseAuth fAuth;

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

        fAuth = FirebaseAuth.getInstance();
        updateUI();
    }

    private void updateUI(){

        if (fAuth.getCurrentUser() != null){
            Log.i("MainActivity", "fAuth != null");
        } else {
            Intent startIntent = new Intent(MainActivity.this, StartActivity.class);
            startActivity(startIntent);
            finish();
            Log.i("MainActivity", "fAuth == null");
        }

    }

}

开始活动

package com.example.myapp;

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

import com.example.myapp.user_sign.RegisterActivity;
import com.google.firebase.auth.FirebaseAuth;

public class StartActivity extends AppCompatActivity {

    private Button reg_btn, log_btn;
    private FirebaseAuth fAuth;

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

        reg_btn =  findViewById(R.id.start_register_btn);
        log_btn =  findViewById(R.id.start_login_btn);

        fAuth = FirebaseAuth.getInstance();
        updateUI();

        reg_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                register();
            }
        }); // end of onclick listener for sign up button

        log_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                login();
            }
        }); // end of onclick listener for log in button
    }

    private void register(){

        Intent regIntent = new Intent(StartActivity.this, RegisterActivity.class);
        startActivity(regIntent);
    }

    private void login (){


    }

    private void updateUI() {
        if (fAuth.getCurrentUser() != null){
            Log.i("StartActivity", "fAuth != null");
            Intent startIntent = new Intent(StartActivity.this, MainActivity.class);
            startActivity(startIntent);
            finish();
        } else {

            Log.i("StartActivity", "fAuth == null");
        }
    }

}

注册活动

package com.example.myapp.user_sign;

import android.app.ProgressDialog;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.design.widget.TextInputLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.example.myapp.MainActivity;
import com.example.myapp.R;
import com.example.myapp.StartActivity;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class RegisterActivity extends AppCompatActivity {

    private Button btnReg;
    private TextInputLayout inName, inEmail, inPassword;

    private FirebaseAuth fAuth;
    private DatabaseReference fUserDatabase;
    private ProgressDialog progressDialog;

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

        btnReg =  findViewById(R.id.reg_btn);
        inName =  findViewById(R.id.input_reg_name);
        inEmail =  findViewById(R.id.input_reg_email);
        inPassword =  findViewById(R.id.input_reg_pswrd);

        fAuth = FirebaseAuth.getInstance();
        fUserDatabase = FirebaseDatabase.getInstance().getReference().child("Users");

        btnReg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String uname = inName.getEditText().getText().toString().trim();
                String uemail = inEmail.getEditText().getText().toString().trim();
                String upswrd = inPassword.getEditText().getText().toString().trim();

                registerUser(uname, uemail, upswrd);
            }
        }); // end of register button on click listener

    }


    private void registerUser (final String name, String email, String pswrd) {

        progressDialog = new ProgressDialog(this);
        progressDialog.setMessage("Processing request, please wait...");
        progressDialog.show();

        fAuth.createUserWithEmailAndPassword(email,pswrd).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {

                if (task.isSuccessful()) {
                    fUserDatabase.child(fAuth.getCurrentUser().getUid()).child("Basic").child("Name")
                            .setValue(name).addOnCompleteListener(new OnCompleteListener<Void>() {

                        @Override
                        public void onComplete(@NonNull Task<Void> task) {

                            if (task.isSuccessful()) {
                                progressDialog.dismiss();
                                Intent mainIntent = new Intent(RegisterActivity.this, MainActivity.class);
                                startActivity(mainIntent);
                                finish();
                                Toast.makeText(RegisterActivity.this, "User register successful!", Toast.LENGTH_SHORT);
                            } else {
                                progressDialog.dismiss();
                                Toast.makeText(RegisterActivity.this, "Error: " + task.getException().getMessage(), Toast.LENGTH_SHORT);
                            }
                        }

                    }); // Listener end


                } else {
                        progressDialog.dismiss();
                        Toast.makeText(RegisterActivity.this, "Error: " + task.getException().getMessage(), Toast.LENGTH_SHORT);
                    }

                }


        });


    }
}

Logcat（仅显示选定的应用程序-这些只是红色部分）

2019-04-03 22:22:24.745 6061-6061/com.example.myapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.myapp, PID: 6061
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapp/com.example.myapp.MainActivity}: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.example.myapp. Make sure to call FirebaseApp.initializeApp(Context) first.
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.example.myapp. Make sure to call FirebaseApp.initializeApp(Context) first.
        at com.google.firebase.FirebaseApp.getInstance(SourceFile:218)
        at com.google.firebase.auth.FirebaseAuth.getInstance(Unknown Source:1)
        at com.example.myapp.MainActivity.onCreate(MainActivity.java:19)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6669) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)