无法转换类型为java.util.Arraylist的对象从Firebase Realtim数据库中读取嵌套对象 [英] Cant convert object of type java.util.Arraylist Read from Firebase realtim database nested objects
问题描述
此Firebase数据库结构:
This Firebase database structure:
这是我的设备类别:
Here is my Device Class:
public class Device {
private String title;
private Map<String,Counters> CounterNumber;
private Counters counters;
public void setCounter(Map<String,Counters> CounterNumber){
this.CounterNumber=CounterNumber;
}
public Map<String,Counters> getCounter(){
return CounterNumber;
}
public Counters getCounters(){
return counters;
}
public void setCounters(Counters counters){
this.counters=counters;
}
public Device(){
}
public Device(String title){
this.title=title;
}
public String getTitle(){
return title;
}
public void setTitle(String title){
this.title=title;
}
}
Second class is my nested object I think
第二类计数器类我的问题是我不知道如何使用
FirebaseUI和RecycleView从数据库中读取Counter对象.
Second class Counters Class My Problem is I don't know how to read
Counterobject from the database withFirebaseUIandRecycleView.
public class Counters implements Serializable {
private String countername;
private String counternumber;
public Counters (){
}
public Counters(String counternumber,String countername){
this.counternumber=counternumber;
this.countername=countername;
}
public String getCounterName() {
return countername;
}
public void setCounterName(String counterName) {
this.countername = countername;
}
public String getCounterNumber() {
return counternumber;
}
public void setCounterNumber(String counternumber) {
this.counternumber = countername;
}
}
这是我的HomeActivity，是从Firebase对象中读取的
This My HomeActivity Here read from firebase objects
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_home, container, false);
recyclerView=(RecyclerView)view.findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
firebaseDatabase=FirebaseDatabase.getInstance();
databaseReference=firebaseDatabase.getReference();
mDevice=new ArrayList<Device>();
mdevices=new Device();
databaseReference.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
if (dataSnapshot != null && dataSnapshot.getValue() != null) {
try {
for (DataSnapshot eventSnapshot : dataSnapshot.getChildren()) {
ArrayList<String> counterse= (ArrayList<String>) eventSnapshot.getValue();
Log.e(TAGE, counterse.toString());
Device device = eventSnapshot.getValue(Device.class);
String id = eventSnapshot.getKey();
Counters counters = eventSnapshot.child(id).getValue(Counters.class);
device.setCounters(counters);
mDevice.add(device);
}
} catch (Exception ex) {
Log.e(TAG, ex.getMessage());
}
}
displayDevices();
}
@Override
public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
return view;
}
private void displayDevices(){
options=
new FirebaseRecyclerOptions.Builder<Device>()
.setQuery(databaseReference.child("devices").orderByChild("user_id").equalTo(userid),Device.class).build();
adapter=
new FirebaseRecyclerAdapter<Device, MyRecyclerViewHolder>(options) {
@Override
protected void onBindViewHolder(@NonNull MyRecyclerViewHolder holder, int position, @NonNull Device model) {
mdevices=mDevice.get(position);
holder.txt_title.setText(model.getTitle());
holder.txt_counter.setText(mdevices.getCounters().getCounterNumber());
Log.i(TAG,mdevices.getCounters().getCounterNumber());
}
@NonNull
@Override
public MyRecyclerViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View itemView= LayoutInflater.from(getContext()).inflate(R.layout.device_list,parent,false);
return new MyRecyclerViewHolder(itemView);
}
};
adapter.startListening();
recyclerView.setAdapter(adapter);
}
@Override
public void onStart() {
adapter.startListening();
super.onStart();
}
@Override
public void onStop() {
super.onStop();
if(adapter != null) {
adapter.stopListening();
}
}
这是我的错误代码 在此处输入图片描述
Here is my Error Code enter image description here
推荐答案
您遇到以下错误:
无法将java.util.ArrayList类型的对象转换为com.example.smartappfirebase.Counters类型
can't convert object of type java.util.ArrayList to type com.example.smartappfirebase.Counters
因为您得到一个ArrayList对象，而不是一个Counters对象，并且在Java中无法创建这样的强制类型转换. cRVh ... NHeT节点内存在的counters节点实际上是一个数组.当您尝试在代码中读取该数组时，它将作为ArrayList读取，因此出现该错误.正如您在屏幕截图中看到的那样，该数组包含Counters个对象.不幸的是，您不能简单地将Counters对象的数组映射到ArrayList<Counters>. counters节点实际上是HashMaps的ArrayList.因此，如果您需要一个ArrayList<Counters>，则应该迭代并自己创建该列表.除此之外，Counters类中的属性名称与数据库中的名称不不匹配.请参见，countername与name和counternumber与counter.所有属性必须匹配.
Because you getting an ArrayList object and not a Counters object and there is no way in Java to create such a cast. Your counters node that exists within the cRVh ... NHeT node is actually an array. When you try to read that array in code, it is read as an ArrayList, hence that error. As I see in your screenshot, that array contains Counters objects. Unfortunately, you cannot simply map that array of Counters objects to an ArrayList<Counters>. The counters node is actually an ArrayList of HashMaps. So if you need to have an ArrayList<Counters>, then you should iterate and create that List yourself. Besides that, the name of the properties in your Counters class do not match the names in the database. See, countername vs name and counternumber vs counter. All properties must match.
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