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我試圖將數據保存到Firebase數據庫。真的沒有那麼複雜，但我發現我的應用程序崩潰，每當我點擊saveInfoButton。我對Swift/iOS的Firebase非常有經驗，但對Android更新。似乎這不會成爲Firebase的問題。Android：App嘗試將數據保存到Firebase數據庫時崩潰
特定消息（當我點擊按鈕時）是：「Restaurant_app已停止，再次打開應用程序。」
activity_main_page.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_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>
UserDetails.java
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;
}
}
MainPage.java
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();
}
}
}
錯誤：
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!
請張貼完整的堆棧跟蹤！ – Chisko
[爲什麼null是一個對象以及null和undefined之間的區別是什麼？]（http://stackoverflow.com/questions/801032/why-is-null-an-object-and-whats-the-difference -between-null-unde-undefined） – Chisko