Java/Android-从Firebase加载ArrayList作为对象时出错
我们已经尝试解决Firebase加载arraylist的问题一段时间了,但不知道如何解决它 对象类Java/Android-从Firebase加载ArrayList作为对象时出错,java,android,firebase,firebase-realtime-database,Java,Android,Firebase,Firebase Realtime Database,我们已经尝试解决Firebase加载arraylist的问题一段时间了,但不知道如何解决它 对象类 public class Book { private String title; private String author; private String ISBN; private String photo; private String ownerEmail; private String ownerID; private Strin
public class Book {
private String title;
private String author;
private String ISBN;
private String photo;
private String ownerEmail;
private String ownerID;
private String BookID;
private Date returnDate;
private Status status;
private String borrowerID;
public Book(){}
public Book(String title, String author, String ISBN, String photo, String ownerEmail, String ownerID) {
this.title = title;
this.author = author;
this.ISBN = ISBN;
this.photo = photo;
this.ownerEmail = ownerEmail;
this.ownerID = ownerID;
this.status = Status.Available;
if(this.BookID == null || this.BookID.isEmpty())
this.BookID = UUID.randomUUID().toString();
}
public enum Status{
Available,
Requested,
Accepted,
Borrowed
}
所有变量都有getter和setter,我要做的是使用代码从firebase加载这些信息:
public void loadMyBookFromFirebase(){
final ArrayList<Book> bookList = new ArrayList<>();
DatabaseReference userReference = FirebaseDatabase.getInstance().getReference().child("users").child(this.userID).child("myBooks");
userReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
Log.d("testing","books" + dataSnapshot.toString());
if(dataSnapshot.exists()) {
try {
for (DataSnapshot books : dataSnapshot.getChildren()) {
Book book = dataSnapshot.getValue(Book.class);
Log.d("testing","books" + book.getAuthor());
//load book into ListView
}
} catch (Exception e){
e.printStackTrace();
}
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.w("testing","Error: ", databaseError.toException());
}
});
}
public void loadMyBookFromFirebase(){
最终ArrayList bookList=新ArrayList();
DatabaseReference userReference=FirebaseDatabase.getInstance().getReference().child(“用户”).child(this.userID).child(“myBooks”);
userReference.addValueEventListener(新的ValueEventListener(){
@凌驾
公共void onDataChange(DataSnapshot DataSnapshot){
Log.d(“测试”、“书籍”+dataSnapshot.toString());
if(dataSnapshot.exists()){
试一试{
对于(DataSnapshot书籍:DataSnapshot.getChildren()){
Book Book=dataSnapshot.getValue(Book.class);
Log.d(“测试”、“书籍”+book.getAuthor());
//将书本加载到ListView中
}
}捕获(例外e){
e、 printStackTrace();
}
}
}
@凌驾
已取消的公共void(@NonNull DatabaseError DatabaseError){
Log.w(“测试”,“错误:”,databaseError.toException());
}
});
}
这是我的firebase数据库
我不断地得到一份工作
无法将类型为java.util.ArrayList
的对象转换为类型com.example.cmput301w19t15.Book
行Book Book=dataSnapshot.getValue(Book.class)上出错代码>
我不知道为什么会出现convert对象错误,我不想搜索单个变量并设置它们,这会破坏对象类的用途
我真的很想了解一下这个问题。要解决这个问题,请更改以下代码行:
Book book = dataSnapshot.getValue(Book.class);
到
您需要从books
对象获取数据,而不是从dataSnapshot
对象获取数据。请上传数据库结构数据库很多,这是一个疏忽,根本没有注意到
Book book = books.getValue(Book.class);