我想从我的firestone db加载RecyclerView。我的firestore结构是这样的：
用户（集合） - > user_id（文档） - >书籍（集合） 书籍（收藏） - > book_id（文件）
补充：数据库结构图像 enter image description here enter image description here enter image description here
我想要做的是将current_user的book_ids变成ArrayList<String>，然后使用这个arraylist，对于每个循环，我想将书籍加载到另一个ArrayList<Book>。我正在获取当前用户的“ArrayList book_ids”。 （我想展示当前用户添加的书籍）
问题是这个数组列表我无法得到ArrayList<Book>books。我将这个数组列表发送到Recycler视图适配器。
public void getBookIdsFromDb(){
final ArrayList<String> myBookIds = new ArrayList<String>();
CollectionReference bookIdRef = db.collection(getString(R.string.collection_users)).document(userId)
.collection(getString(R.string.colleciton_books));
bookIdRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
@Override
public void onComplete(@NonNull com.google.android.gms.tasks.Task<QuerySnapshot> task) {
if (task.isSuccessful()){
for (DocumentSnapshot ds : task.getResult()){
myBookIds.add(ds.getString("book_id"));
myBookIds.size());
}
Log.d(TAG, "onComplete: myBookIds.size" + myBookIds.size());
if (myBookIds.size()>0){
getMyBooksFromDb(myBookIds);
//this works
}
}
}
});
}
public void getMyBooksFromDb(ArrayList<String> bookIds){
final ArrayList<String> myBooksIds =bookIds;
final ArrayList<Book> myBooks = new ArrayList<Book>();
CollectionReference dbRef = db.collection(getString(R.string.colleciton_books));
for (int i =0; i<myBooksIds.size();i++){
Log.d(TAG, "getMyBooksFromDb: myBookIds in for " + myBooksIds.size());
dbRef.document(myBooksIds.get(i)).get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
@Override
public void onSuccess(DocumentSnapshot documentSnapshot) {
if (documentSnapshot != null){
Book myBook = documentSnapshot.toObject(Book.class);
myBooks.add(myBook);
//Can not get out of this array from for loop
}
}
});
}
}
//I tried to make a nested query below but no result :(
public void getBookListFromDb(){
final ArrayList<String> myBookIds = new ArrayList<String>();
CollectionReference bookIdRef = db.collection(getString(R.string.collection_users)).document(userId)
.collection(getString(R.string.colleciton_books));
bookIdRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
@Override
public void onComplete(@NonNull com.google.android.gms.tasks.Task<QuerySnapshot> task) {
final ArrayList<Book> myBooks = new ArrayList<Book>();
if (task.isSuccessful()){
for (DocumentSnapshot ds : task.getResult()){
myBookIds.add(ds.getString("book_id"));
myBookIds.size();
}
Log.d(TAG, "onComplete: myBookIds.size" + myBookIds.size());
if (myBookIds.size()>0){
CollectionReference colRef = db.collection(getString(R.string.colleciton_books));
for (int i=0; i< myBookIds.size(); i++){
colRef.document(myBookIds.get(i)).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull com.google.android.gms.tasks.Task<DocumentSnapshot> task) {
if (task.isSuccessful()){
DocumentSnapshot ds = task.getResult();
Book myBook = ds.toObject(Book.class);
myBooks.add(myBook);
}
Log.d(TAG, "onComplete: myBooks.size(i) "+ myBooks.size());
}
});
Log.d(TAG, "onComplete: myBooks.size() in for "+ myBooks.size());
}
Log.d(TAG, "onComplete: myBooks.size() "+ myBooks.size());
}
}
}
});
}'
你无法以这种方式实现你想要的东西，因为onComplete()和onSuccess()这两种方法都有异步行为。这意味着当您调用getMyBooksFromDb()方法时，您还没有从数据库中获取数据。因此，要解决此问题，您需要在getMyBooksFromDb()方法中移动onComplete()方法中的所有逻辑。这是流程：
book_idonComplete()方法内使用book_id创建你的CollectionReference来寻找书籍。ArrayList<Book>方法中移动onSuccess()的声明。Book对象执行您想要的操作。所以解决方案是使用嵌套查询，如上所述。所以请使用以下代码：
CollectionReference bookIdRef = db.collection(getString(R.string.collection_users))
.document(userId)
.collection(getString(R.string.colleciton_books));
bookIdRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
@Override
public void onComplete(@NonNull com.google.android.gms.tasks.Task<QuerySnapshot> task) {
if (task.isSuccessful()){
for (DocumentSnapshot ds : task.getResult()) {
String bookId = myBookIds.add(ds.getString("book_id"));
dbRef.document(bookId).get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
@Override
public void onSuccess(DocumentSnapshot documentSnapshot) {
if (documentSnapshot != null){
Book myBook = documentSnapshot.toObject(Book.class);
Log.d("TAG", myBoog.getBookName());
}
}
});
}
}
}
});
步骤1：
创建一个Userbook.java和Book.java的模型类
Userbook.Java
String book_id;
Book book;
//create getter and setter for that.
根据您的代码设置值：
UserBook userbook = new UserBook();
final ArrayList<UserBook> books = new ArrayList<String>();
public void getBookIdsFromDb(){
CollectionReference bookIdRef = db.collection(getString(R.string.collection_users)).document(userId)
.collection(getString(R.string.colleciton_books));
bookIdRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
@Override
public void onComplete(@NonNull com.google.android.gms.tasks.Task<QuerySnapshot> task) {
if (task.isSuccessful()){
for (DocumentSnapshot ds : task.getResult()){
userbook.setBook_id(ds.getString("book_id"));
}
Log.d(TAG, "onComplete: myBookIds.size" + myBookIds.size());
if (myBookIds.size()>0){
getMyBooksFromDb(myBookIds);
//this works
}
}
}
});
}
public void getMyBooksFromDb(ArrayList<String> bookIds){
CollectionReference dbRef = db.collection(getString(R.string.colleciton_books));
for (int i =0; i<myBooksIds.size();i++){
Log.d(TAG, "getMyBooksFromDb: myBookIds in for " + myBooksIds.size());
dbRef.document(myBooksIds.get(i)).get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
@Override
public void onSuccess(DocumentSnapshot documentSnapshot) {
if (documentSnapshot != null){
Book myBook = documentSnapshot.toObject(Book.class);
userbook.setBook_id(myBook);
//Can not get out of this array from for loop
}
}
});
}
}
//after all this add obj to list
books.add(userbook);
我希望你能得到结果。或者ping这里。