问Android:尝试将数据保存到Firebase数据库时应用程序崩溃

EN

<?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_page"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="16dp"
    android:paddingLeft="64dp"
    android:paddingRight="64dp"
    android:paddingTop="16dp"
    tools:context="com.example.test.restaurant_app.MainPage">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true">

        <TextView
            android:text="Email"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:textAppearance="?android:attr/textAppearanceLarge"
            android:id="@+id/userEmail" />

        <EditText
            android:layout_margin="15dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="textEmailAddress"
            android:hint="Enter your name"
            android:id="@+id/nameTextField"
            />

        <EditText
            android:layout_margin="15dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="text"
            android:hint="address"
            android:id="@+id/addressTextField"
            />
        <EditText
            android:layout_margin="15dp"
            android:id="@+id/ageTextField"
            android:hint="Age"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
        <Button
            android:layout_margin="15dp"
            android:id="@+id/saveInfoButton"
            android:text="Save Information"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
        <Button
            android:text="Logout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:id="@+id/logoutButton" />
    </LinearLayout>
</RelativeLayout>

package com.example.test.restaurant_app;

public class UserDetails {

    public String name;
    public String address;
    public int age;

    public UserDetails(String name, String address, int age) {
        this.name = name;
        this.address = address;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

package com.example.test.restaurant_app;

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

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

public class MainPage extends AppCompatActivity implements View.OnClickListener {

    private FirebaseAuth mAuth;
    private FirebaseUser user;
    private TextView textViewEmail;
    private Button logoutButton;
    private DatabaseReference dbReference;

    private EditText editTextName, editTextAddress, editTextAge;
    private Button saveInfo;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        mAuth = FirebaseAuth.getInstance();


        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_page);

        logoutButton = (Button) findViewById(R.id.logoutButton);
        textViewEmail = (TextView) findViewById(R.id.userEmail);
        editTextName = (EditText) findViewById(R.id.nameTextField);
        editTextAddress = (EditText) findViewById(R.id.addressTextField);
        editTextAge = (EditText) findViewById(R.id.ageTextField);
        saveInfo = (Button) findViewById(R.id.saveInfoButton);

        if (mAuth.getCurrentUser() == null) {
            finish();
            startActivity(new Intent(getApplicationContext(), LoginActivity.class));
        }

        FirebaseUser user = mAuth.getCurrentUser();
        String name = user.getEmail().toString().trim();
        String welcomeMessage = "Hello, " + name;
        textViewEmail.setText(welcomeMessage);

        logoutButton.setOnClickListener(this);
        saveInfo.setOnClickListener(this);

    }

    public void saveInfo() {
        String name = editTextName.getText().toString();
        String address = editTextAddress.getText().toString();
        int age = Integer.parseInt(editTextAge.getText().toString());

        UserDetails userInfo = new UserDetails(name, address, age);

        dbReference.child("Users").child(user.getUid()).setValue(userInfo);

        Toast.makeText(this, "Information Saved", Toast.LENGTH_LONG).show();

    }

    public void onClick(View view) {
        if (view == logoutButton) {
            finish();
            startActivity(new Intent(getApplicationContext(), LoginActivity.class));
        }
        if (view == saveInfo){
            saveInfo();
        }
        }
    }

03-15 11:33:41.516 4595-4595/com.example.test.restaurant_app E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                     Process: com.example.test.restaurant_app, PID: 4595
                                                                                     java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.database.DatabaseReference com.google.firebase.database.DatabaseReference.child(java.lang.String)' on a null object reference
                                                                                         at com.example.test.restaurant_app.MainPage.saveInfo(MainPage.java:65)
                                                                                         at com.example.test.restaurant_app.MainPage.onClick(MainPage.java:77)
                                                                                         at android.view.View.performClick(View.java:5637)
                                                                                         at android.view.View$PerformClick.run(View.java:22429)
                                                                                         at android.os.Handler.handleCallback(Handler.java:751)
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                         at android.os.Looper.loop(Looper.java:154)
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

03-15 11:33:41.521 1605-1828/system_process W/ActivityManager:   Force finishing activity com.example.test.restaurant_app/.MainPage

03-15 11:33:41.554 1326-2029/? D/gralloc_ranchu: gralloc_alloc: format 1 and usage 0x900 imply creation of host color buffer

03-15 11:33:41.557 1326-2029/? D/gralloc_ranchu: gralloc_alloc: format 1 and usage 0x900 imply creation of host color buffer

03-15 11:33:41.558 1326-2029/? D/gralloc_ranchu: gralloc_alloc: format 1 and usage 0x900 imply creation of host color buffer

03-15 11:33:41.559 1605-3137/system_process I/OpenGLRenderer: Initialized EGL, version 1.4

03-15 11:33:41.559 1605-3137/system_process D/OpenGLRenderer: Swap behavior 1

03-15 11:33:41.560 1605-3137/system_process W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...

03-15 11:33:41.560 1605-3137/system_process D/OpenGLRenderer: Swap behavior 0

03-15 11:33:42.027 1605-1619/system_process W/ActivityManager: Activity pause timeout for ActivityRecord{7bfe46d u0 com.example.test.restaurant_app/.MainPage t644 f}

03-15 11:33:46.545 2380-5115/com.google.android.gms W/PlatformStatsUtil: Could not retrieve Usage & Diagnostics setting. Giving up.

03-15 11:33:51.529 1605-1619/system_process W/ActivityManager: Launch timeout has expired, giving up wake lock!