我是 Android Studio 编码初学者，目前正在构建营养应用以进行编程练习。我使用 Firebase 进行身份验证，并作为数据库来保存用户数据。
工作原理:
我的应用内置了一项调查，询问 body 特征和口味(年龄、高度、喜欢/不喜欢的成分等)。我有一个具有公共(public)静态属性的 GlobalUser 类，用于将答案保存在应用程序中。当用户注册时，他将被直接发送到调查 Activity 。他在那里回答问题，并将结果写入他的 UID 下的 Firebase 数据库(我使用具有与 GlobalUser 相同属性的 User 类来创建实例并使用 Firebase 的 setValue(Object) 方法)。如果他登录(或仍然登录)，LoginRegistrationActivity 会直接将他发送到 MainActivity。在那里，GlobalUser 类使用保存在其 UID 下的数据进行实例化。他可以从 MainActivity 导航到 ProfileActivity，在其中 UI 根据他的数据进行更新。这很好用。完成调查后，我可以在包含用户 UID 的子节点中找到结果，UI 得到正确更新，并且登录/注册过程按预期进行。
出了什么问题:
但是，当我尝试不同的设计并不断重启应用程序时，它偶尔会崩溃。经过一些测试后，它表明 GlobalUser 类没有更新，因此 ArrayLists 为 null 并在我对它们使用 .size() 时导致 NullPointerExceptions。由于此问题很少发生，并且似乎与多次重启应用程序有关，我认为这与 Activity 生命周期有关，因此我还在 onStart 和 onResume 中更新了 GlobalUser，但它没有帮助。我还尝试在设置 ArrayLists 之前直接在 ProfileActivity 中再次更新 GlobalUser，但它没有用。我仍然猜想它与生命周期有关，但我不知道应该从哪里开始。这是相关类(class)/Activity 的代码:
登录注册 Activity :
public class LoginRegistrationActivity extends AppCompatActivity {
private DatabaseReference mRef;
private FirebaseAuth mAuth;
private EditText emailAddress;
private EditText emailPassword;
private Button emailLogin;
private Button emailRegistration;
private TextView forgotPassword;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login_registration);
mAuth = FirebaseAuth.getInstance();
if (mAuth.getCurrentUser()!=null){
Intent i = new Intent (LoginRegistrationActivity.this, MainActivity.class);
LoginRegistrationActivity.this.startActivity(i);
}
emailAddress = findViewById(R.id.address_edit);
emailPassword = findViewById(R.id.password_edit);
emailLogin = findViewById(R.id.mail_login_button);
emailRegistration = findViewById(R.id.mail_registration_button);
forgotPassword = findViewById(R.id.forgot_password);
emailRegistration.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String email = emailAddress.getText().toString().trim();
String password = emailPassword.getText().toString().trim();
if (TextUtils.isEmpty(email)){
Toast.makeText(LoginRegistrationActivity.this, "Bitte E-Mail Addresse eingeben!", Toast.LENGTH_LONG).show();
return;
}
if (TextUtils.isEmpty(password)){
Toast.makeText(LoginRegistrationActivity.this, "Bitte Passwort eingeben!", Toast.LENGTH_LONG).show();
return;
}
if (password.length()<6){
Toast.makeText(LoginRegistrationActivity.this, "Passwort muss mindestens sechs Zeichen lang sein!", Toast.LENGTH_LONG).show();
return;
}
mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(LoginRegistrationActivity.this, new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if (!task.isSuccessful()){
Toast.makeText(LoginRegistrationActivity.this, "Unbekannter Fehler", Toast.LENGTH_LONG).show();
} else {
Intent i = new Intent (LoginRegistrationActivity.this, SurveyGreetingActivity.class);
LoginRegistrationActivity.this.startActivity(i);
finish();
}
}
});
}
});
emailLogin.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String password = emailPassword.getText().toString();
String email = emailAddress.getText().toString();
if (TextUtils.isEmpty(email)){
Toast.makeText(LoginRegistrationActivity.this, "Bitte E-Mail Addresse eingeben!", Toast.LENGTH_LONG).show();
return;
}
if (TextUtils.isEmpty(password)){
Toast.makeText(LoginRegistrationActivity.this, "Bitte Passwort eingeben!", Toast.LENGTH_LONG).show();
return;
}
if (password.length()<6){
Toast.makeText(LoginRegistrationActivity.this, "Passwort muss mindestens sechs Zeichen haben!", Toast.LENGTH_LONG).show();
return;
}
mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(LoginRegistrationActivity.this, new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if (!task.isSuccessful()){
Toast.makeText(LoginRegistrationActivity.this, "Unbekannter Fehler beim Einloggen", Toast.LENGTH_LONG).show();
} else {
Intent i = new Intent (LoginRegistrationActivity.this, MainActivity.class);
LoginRegistrationActivity.this.startActivity(i);
finish();
}
}
});
}
});
}
}
主要 Activity :
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final FirebaseAuth mAuth = FirebaseAuth.getInstance();
FirebaseUser user = mAuth.getCurrentUser();
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference mRef = database.getReference().child("users").child("uid").child(mAuth.getCurrentUser().getUid());
//In case the user cancelled the app when filling out the survey for the first time
if (mRef == null){
MainActivity.this.startActivity(new Intent (MainActivity.this, SurveyGreetingActivity.class));
}
//sets GlobalUser to data saved in Firebase Database User object
mRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
User user = dataSnapshot.getValue(User.class);
if (user!=null){
GlobalUser.setToUser(user);
GlobalUser.setGlobalUid(mAuth.getCurrentUser().getUid());
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(getApplicationContext(), "Database Error", Toast.LENGTH_LONG).show();
}
});
}
}
全局用户:
package com.example.andre.valetto02;
import java.util.ArrayList;
public class GlobalUser {
public static String globalUid = null;
public static ArrayList<Ingredient> globalLikes;
public static ArrayList<Ingredient> globalDislikes;
public static int globalAge;
public static int globalWeight;
public static int globalHeight;
public static int globalTrainingGoal;
public static int globalDailyActive;
public static boolean globalIsMale;
public GlobalUser() {
}
public static String getGlobalUid() {
return globalUid;
}
public static void setGlobalUid(String globalUid) {
GlobalUser.globalUid = globalUid;
}
public static ArrayList<Ingredient> getGlobalLikes() {
return globalLikes;
}
public static void setGlobalLikes(ArrayList<Ingredient> globalLikes) {
GlobalUser.globalLikes = globalLikes;
}
public static ArrayList<Ingredient> getGlobalDislikes() {
return globalDislikes;
}
public static void setGlobalDislikes(ArrayList<Ingredient> globalDislikes) {
GlobalUser.globalDislikes = globalDislikes;
}
public static int getGlobalAge() {
return globalAge;
}
public static void setGlobalAge(int globalAge) {
GlobalUser.globalAge = globalAge;
}
public static int getGlobalWeight() {
return globalWeight;
}
public static void setGlobalWeight(int globalWeight) {
GlobalUser.globalWeight = globalWeight;
}
public static int getGlobalHeight() {
return globalHeight;
}
public static void setGlobalHeight(int globalHeight) {
GlobalUser.globalHeight = globalHeight;
}
public static int getGlobalTrainingGoal() {
return globalTrainingGoal;
}
public static void setGlobalTrainingGoal(int globalTrainingGoal) {
GlobalUser.globalTrainingGoal = globalTrainingGoal;
}
public static int getGlobalDailyActive() {
return globalDailyActive;
}
public static void setGlobalDailyActive(int globalDailyActive) {
GlobalUser.globalDailyActive = globalDailyActive;
}
public static boolean isGlobalIsMale() {
return globalIsMale;
}
public static void setGlobalIsMale(boolean globalIsMale) {
GlobalUser.globalIsMale = globalIsMale;
}
public static void setToUser(User user) {
GlobalUser.setGlobalAge(user.getAge());
GlobalUser.setGlobalWeight(user.getWeight());
GlobalUser.setGlobalHeight(user.getHeight());
GlobalUser.setGlobalDailyActive(user.getDailyActive());
GlobalUser.setGlobalTrainingGoal(user.getTrainingGoal());
GlobalUser.setGlobalIsMale(user.getIsMale());
GlobalUser.setGlobalLikes(user.getLikes());
GlobalUser.setGlobalDislikes(user.getDislikes());
}
public static void resetLikesAndDislikes(){
globalLikes = new ArrayList <>();
globalDislikes = new ArrayList<>();
}
public static User globalToUser () {
return new User (globalLikes, globalDislikes, globalWeight, globalHeight, globalAge, globalTrainingGoal, globalDailyActive, globalIsMale);
}
}
用户:
package com.example.andre.valetto02;
import java.util.ArrayList;
public class User {
ArrayList<Ingredient> likes;
ArrayList<Ingredient> dislikes;
Boolean isMale;
public Boolean getIsMale(){return isMale;}
public void setIsMale(Boolean b){isMale = b;}
public void setDislikes(ArrayList<Ingredient> dislikes) {
this.dislikes = dislikes;
}
public User (){
likes = new ArrayList<>();
dislikes = new ArrayList<>();
weight = 0;
height = 0;
age = 0;
trainingGoal = 2;
dailyActive = 1;
isMale=true;
}
public User (ArrayList<Ingredient> l, ArrayList<Ingredient> d, int w, int h, int a, int tG, int dA, boolean iM) {
likes = l;
dislikes = d;
weight = w;
height = h;
age = a;
trainingGoal = tG;
dailyActive = dA;
isMale = iM;
}
int age;
public ArrayList<Ingredient> getDislikes() {
return dislikes;
}
public ArrayList<Ingredient> getLikes() {
return likes;
}
public void setLikes (ArrayList<Ingredient> list){
likes = list;
}
public void setDisikes (ArrayList<Ingredient> list){
dislikes = list;
}
public int getAge () {
return age;
}
public void setAge (int i) {
age = i;
}
int weight;
public int getWeight (){
return weight;
}
public void setWeight(int i) {
weight = i;
}
int height;
public int getHeight (){
return height;
}
public void setHeight(int i) {
height = i;
}
int trainingGoal; //trainingGoal = 0 means weight loss, 1 means muscle gain and 2 means healthy living
public void setTrainingGoal(int i) {
trainingGoal = i;
}
public int getTrainingGoal(){
return trainingGoal;
}
int dailyActive; //dailyActive = 0 means wenig, 1 means leicht, 2 means moderat, 3 means sehr and 4 means extrem
public int getDailyActive() {return dailyActive;}
public void setDailyActive(int i) {dailyActive = i;}
public double computeCalorieGoal(){
if (isMale) {
double RMR;
RMR = weight*10 + 6.25*height - 5*age + 5;
if (dailyActive==0) {RMR=RMR*1.2;}
else if (dailyActive==1) {RMR=RMR*1.375;}
else if (dailyActive==2) {RMR=RMR*1.55;}
else if (dailyActive==3) {RMR=RMR*1.725;}
else {RMR=RMR*1.9;}
if (trainingGoal == 0) {RMR = RMR - 400;}
else if (trainingGoal ==1){RMR = RMR + 400;}
return RMR;
} else {
double RMR;
RMR = weight*10 + 6.25*height - 5*age - 161;
if (dailyActive==0) {RMR=RMR*1.2;}
else if (dailyActive==1) {RMR=RMR*1.375;}
else if (dailyActive==2) {RMR=RMR*1.55;}
else if (dailyActive==3) {RMR=RMR*1.725;}
else {RMR=RMR*1.9;}
if (trainingGoal == 0) {RMR = RMR - 300;}
else if (trainingGoal ==1){RMR = RMR + 300;}
return RMR;
}
}
}
感谢您的帮助!
最佳答案
我刚刚发现错误。它与 Activity 生命周期无关，只是间接地与重启应用程序有关。问题是 Firebase 的值事件监听器仍然是 AsyncTasks。当我启动应用程序并立即打开 ProfileActivity 时，Activity 在 Firebase AsyncTask 可以从数据库中获取数据之前创建。因此 ProfileActivity 会在 ArrayLists 被实例化之前调用 .size() 方法。从本质上讲，当您通过 UI 单击速度过快并且比异步数据获取任务更快时，就会发生错误。
因此我将 session 管理移动到 LoginRegistrationActivity，如下所示:
if (mAuth.getCurrentUser()!=null){
FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();
DatabaseReference mRef = firebaseDatabase.getReference().child("users").child("uid").child(mAuth.getCurrentUser().getUid());
//In case the user cancelled the app when filling out the survey for the first time
if (mRef == null){
LoginRegistrationActivity.this.startActivity(new Intent (LoginRegistrationActivity.this, SurveyGreetingActivity.class));
}
mRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
User user = dataSnapshot.getValue(User.class);
if (user!=null) {
GlobalUser.setToUser(user);
GlobalUser.setGlobalUid(mAuth.getCurrentUser().getUid());
}
Intent i = new Intent (LoginRegistrationActivity.this, MainActivity.class);
LoginRegistrationActivity.this.startActivity(i);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
通过将 LoginRegistrationActivity.this.startActivity(i) 移动到 onDataChange 方法，我确保在启动 MainActivity 之前实例化 GlobalUser 变量。可能还有更优雅的方法可以做到这一点。
关于java - Firebase session 管理 : Issues with instatiating Global User，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/51456638/