从Firestore获取数据后，字符串不会添加到OnClick Listener中的ArrayList中

Question

我试图在FirebaseFirestore中创建一个Forum应用程序，我已经让它显示主题，但当我想添加新主题时，它会从集合中获取用户数据("fname"one_answers"lname"并将它们放在一起作为一个名称(，但它似乎没有将它们添加到ArrayList中，因为它是从OnComplete函数调用的，所以必须声明为final。我得到这个错误：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.mechachromemobileapp, PID: 15590
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.get(ArrayList.java:437)
at com.example.mechachromemobileapp.ForumPostTopic$1.onClick(ForumPostTopic.java:91)
at android.view.View.performClick(View.java:6256)
at android.view.View$PerformClick.run(View.java:24701)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

这表明数组是空的，如果你知道如何更新它，我将不胜感激，或者也许可以用另一种方法，也许可以做一些更简单的事情来实现结果。代码如下：

public class ForumPostTopic extends AppCompatActivity {
public static final String TAG = "TAG";
EditText editTopic, editContent;
Button addTopicBtn;
FirebaseFirestore fStore;
FirebaseAuth fAuth;
Date date_published;
String userID;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_forum_post_topic);
editTopic = findViewById(R.id.editTopic);
editContent = findViewById(R.id.editContent);
addTopicBtn = findViewById(R.id.addTopicBtn);
fAuth = FirebaseAuth.getInstance();
userID = fAuth.getCurrentUser().getUid();
fStore = FirebaseFirestore.getInstance();
date_published = Calendar.getInstance().getTime();

addTopicBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String topic = editTopic.getText().toString().trim();
String content = editContent.getText().toString().trim();
final ArrayList<String> author = new ArrayList<>();

// getting the user
DocumentReference userRef = fStore.collection("users").document(userID);
userRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
DocumentSnapshot user = task.getResult();
if(task.isSuccessful()) {
if (user.exists()) {
Log.d(TAG,"Got the user " + userID);
String author_temp = user.get("fname").toString() + " " + user.get("lname").toString();
author.add(0,author_temp);
} else {
Log.d(TAG,"No such user");
}
notifyAll();
}
else {
Log.d(TAG, "get failed with ", task.getException());
}
}
});

// setting the topic
DocumentReference topicRef = fStore.collection("forum_topics").document();
Map<String, Object> addTopic = new HashMap<>();
addTopic.put("topic_name", topic);
addTopic.put("date_published", date_published);
addTopic.put("author", author.get(0));
topicRef.set(addTopic).addOnSuccessListener(new OnSuccessListener<Void>() {
@Override
public void onSuccess(Void aVoid) {
Log.d(TAG,"New Topic document created");
}
});
// setting the post
DocumentReference postRef = fStore.collection("forum_posts").document();
Map<String, Object> addPost = new HashMap<>();
addPost.put("topic_name", topic);
addPost.put("date_published", date_published);
addPost.put("author", author.get(0);
addPost.put("content", content);
postRef.set(addPost).addOnSuccessListener(new OnSuccessListener<Void>() {
@Override
public void onSuccess(Void aVoid) {
Log.d(TAG,"New Post document created");
}
});
}
});

}

}

谢谢你的回答！

Answer 1

这是因为，

addTopic.put("author", author.get(0));
addPost.put("author", author.get(0);

在onComplete上获得回调之前执行。因此，当您尝试访问author[0]时，它什么都没有，并且会发生AIOB异常。尝试设置主题&在onComplete中得到响应后设置帖子。

public class ForumPostTopic extends AppCompatActivity {
public static final String TAG = "TAG";
EditText editTopic, editContent;
Button addTopicBtn;
FirebaseFirestore fStore;
FirebaseAuth fAuth;
Date date_published;
String userID;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_forum_post_topic);
editTopic = findViewById(R.id.editTopic);
editContent = findViewById(R.id.editContent);
addTopicBtn = findViewById(R.id.addTopicBtn);
fAuth = FirebaseAuth.getInstance();
userID = fAuth.getCurrentUser().getUid();
fStore = FirebaseFirestore.getInstance();
date_published = Calendar.getInstance().getTime();

addTopicBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final ArrayList<String> author = new ArrayList<>();

// getting the user
DocumentReference userRef = fStore.collection("users").document(userID);
userRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
DocumentSnapshot user = task.getResult();
if(task.isSuccessful()) {
if (user.exists()) {
Log.d(TAG,"Got the user " + userID);
String author_temp = user.get("fname").toString() + " " + user.get("lname").toString();
author.add(0,author_temp);
setTopic(author);
setPost(author);
} else {
Log.d(TAG,"No such user");
}
notifyAll();
}
else {
Log.d(TAG, "get failed with ", task.getException());
}
}
});
}
});
}
private void setTopic(ArrayList<String> author){
String topic = editTopic.getText().toString().trim();
DocumentReference topicRef = fStore.collection("forum_topics").document();
Map<String, Object> addTopic = new HashMap<>();
addTopic.put("topic_name", topic);
addTopic.put("date_published", date_published);
addTopic.put("author", author.get(0));
topicRef.set(addTopic).addOnSuccessListener(new OnSuccessListener<Void>() {
@Override
public void onSuccess(Void aVoid) {
Log.d(TAG,"New Topic document created");
}
});
}
private void setPost(ArrayList<String> author){
String topic = editTopic.getText().toString().trim();
String content = editContent.getText().toString().trim();
DocumentReference postRef = fStore.collection("forum_posts").document();
Map<String, Object> addPost = new HashMap<>();
addPost.put("topic_name", topic);
addPost.put("date_published", date_published);
addPost.put("author", author.get(0);
addPost.put("content", content);
postRef.set(addPost).addOnSuccessListener(new OnSuccessListener<Void>() {
@Override
public void onSuccess(Void aVoid) {
Log.d(TAG,"New Post document created");
}
});
}
}