空ArrayList-Firebase数据检索 [英] Empty ArrayList - Firebase Data Retrieval
问题描述
我目前正在尝试在Firebase数据库上运行查询,我可以在日志中看到所需的值,但是我的方法始终返回一个空的数组列表.
I am currently trying to run a query on my firebase DB, I can see the values that I want in my logs but my method always returns an empty arraylist.
请在下面找到我的代码:
Kindly find my code below:
public static ArrayList<Transaction> getUserTransactions(String userId){
Query userTransactionQuery = mDatabaseReference
.child("transactions")
.orderByChild("userId")
.equalTo(userId);
final ArrayList<Transaction> transactionsByUser = new ArrayList<>();
userTransactionQuery.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot transactionSnapshot: dataSnapshot.getChildren()) {
// TODO: handle the post
Transaction t = transactionSnapshot.getValue(Transaction.class);
transactionsByUser.add(t);
Log.w(TAG, t.toString());
}
Log.i(TAG, "Collected User Transactions");
}
@Override
public void onCancelled(DatabaseError databaseError) {
// Getting Transaction failed, log a message
Log.w(TAG, "loadTransactions:onCancelled", databaseError.toException());
// ...
}
});
return transactionsByUser;
}
我的POJO:
public class Transaction {
private String id;
private String userId;
private String categoryId;
private TransactionType transactionType;
private String creationDate;
private long amount;
private String description;
/**
* No args constructor
*/
public Transaction () {}
/**
* Constructor for the Transaction object
* @param userId id of the user who made the transaction
* @param categoryId ID of the category the transaction belongs under
* @param amount amount spent/received
* @param transactionType income/expense
*/
public Transaction(String userId, String categoryId, TransactionType transactionType, long amount, String description) {
this.userId = userId;
this.categoryId = categoryId;
this.transactionType = transactionType;
this.amount = amount;
this.description = description;
//Date last changed will always be set to ServerValue.TIMESTAMP
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
String currentDateTime = dateFormat.format(new Date()); // Find todays date
this.creationDate = currentDateTime;
}
/**
* Transaction Id Getter
* @return transaction Id
*/
public String getId() {
return id;
}
/**
* Transaction Id Setter
* @param id Id to assign to the user
*/
public void setId(String id) {
this.id = id;
}
/**
* Category Id getter
* @return category Id under which the transaction belongs
*/
public String getCategoryId() {
return categoryId;
}
/**
* Category Id setter
* @param categoryId category Id under which the transaction belongs
*/
public void setCategoryId(String categoryId) {
this.categoryId = categoryId;
}
/**
* Transaction type getter
* @return type of the transaction whether its an income or an expense
*/
public TransactionType getTransactionType() {
return transactionType;
}
/**
* Transaction type setter
* @param transactionType type of the transaction to set
*/
public void setTransactionType(TransactionType transactionType) {
this.transactionType = transactionType;
}
/**
* Transaction creation date getter
* @return creation date of the transaction
*/
public String getCreationDate() {
return creationDate;
}
/**
* Transaction creation date setter
* @param creationDate creation date to set to the transaction
*/
public void setCreationDate(String creationDate) {
this.creationDate = creationDate;
}
/**
* Transaction amount getter
* @return amount set
*/
public long getAmount() {
return amount;
}
/**
* Transaction amount setter
* @param amount amount to set
*/
public void setAmount(long amount) {
this.amount = amount;
}
/**
* User Id getter
* @return user id corresponding to the transaction
*/
public String getUserId() {
return userId;
}
/**
* User Id setter
* @param userId user id to set to the transaction
*/
public void setUserId(String userId) {
this.userId = userId;
}
/**
* Description getter
* @return Description corresponding to the transaction
*/
public String getDescription() {
return description;
}
/**
* Description setter
* @param description Description to set to the transaction
*/
public void setDescription(String description) {
this.description = description;
}
/**
* Transaction object string representation
* @return object represented in a string
*/
@Override
public String toString() {
return "Transaction{" +
"id='" + id + '\'' +
", userId='" + userId + '\'' +
", categoryId='" + categoryId + '\'' +
", transactionType=" + transactionType +
", creationDate='" + creationDate + '\'' +
", amount=" + amount +
'}';
}
}
我的JSON树如下:
{
transactions:
{
transactionId {
pojo
}
}
}
简而言之:我要做的是使用用户ID来获取用户进行的所有交易,我试图将结果存储在数组列表中,但数组列表始终返回空;
In brief: what I'm trying to do is get all the transactions made by a user using his user ID, Im trying to store the result in an array list but the array list always returns empty;
推荐答案
因此,这只是尝试回答您的问题:
So this is just an attempt to answer your question:
public static void getUserTransactions(String userId, final ArrayList<Transaction> transactionsByUser){
Query userTransactionQuery = mDatabaseReference
.child("transactions")
.orderByChild("userId")
.equalTo(userId);
userTransactionQuery.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot transactionSnapshot: dataSnapshot.getChildren()) {
// TODO: handle the post
Transaction t = transactionSnapshot.getValue(Transaction.class);
transactionsByUser.add(t);
Log.w(TAG, t.toString());
}
Log.i(TAG, "Collected User Transactions");
}
@Override
public void onCancelled(DatabaseError databaseError) {
// Getting Transaction failed, log a message
Log.w(TAG, "loadTransactions:onCancelled", databaseError.toException());
// ...
}
});
}
用法
ArrayList<Transaction> transactions = new ArrayList<>();
getUserTransactions("{userId}", transactions);
//check after method call while debugging if transactions is empty
如果这不起作用,则必须在使用ArrayList的地方使用此事件实现.请注意,Firebase查询是异步的.
If this does not work you going to have to use this event implementation where the ArrayList is being used. Be aware that Firebase queries are asynchronous.
这篇关于空ArrayList-Firebase数据检索的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!