Question

我遇到以下错误

com.google.firebase.database.DatabaseException：无法将java.lang.String类型的对象转换为com.mscit_lab_16.school_management.Message

类型

我遇到了问题

m.setMsg（ds.getValue（Message.class）.getMsg（））;

帮我解决这个错误。

有一个Message类

package com.mscit_lab_16.school_management;

import android.support.annotation.Keep;

import com.google.firebase.database.Exclude;

/**
* Created by PC PLANET on 12/05/2018.
*/
//@JsonIgnoreProperties(ignoreUnknown = true)
@Keep
public class Message {

public String msg;

public Message() {
}

@Keep
public String getMsg() {
    return msg;
}

@Keep
public void setMsg(String msg) {
    this.msg = msg;
}
}

Cont_admin.java

package com.mscit_lab_16.school_management;

import android.app.Dialog;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.firebase.client.Firebase;
import com.google.firebase.FirebaseApp;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.internal.FirebaseAppHelper;
import android.database.Cursor;

import java.util.ArrayList;

public class Cont_Admin extends AppCompatActivity {

EditText msgText;
Button sendBtn;
ArrayList<Message> msgs=new ArrayList<Message>();
RecyclerView rv;
MyAdapter adapter;
DatabaseReference databaseReference;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_cont__admin);
    Toolbar toolbar=(Toolbar)findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    FloatingActionButton fab=(FloatingActionButton)findViewById(R.id.fab);

    rv=findViewById(R.id.mRecyclerID);
    rv.setLayoutManager(new LinearLayoutManager(this));

    databaseReference= FirebaseDatabase.getInstance().getReference("admin_messages");

    Firebase.setAndroidContext(this);

    //REFERENCE
   this.refreshData();
}

public void sendMesssage_admin(View view) {
    displayDialog();
}

private void displayDialog(){
    Dialog d=new Dialog(this);
    d.setTitle("Send Message");
    d.setContentView(R.layout.dialoglayout);

    msgText=d.findViewById(R.id.nameEditText);
    sendBtn=d.findViewById(R.id.sendBtn);

    d.show();
}

public void sendMsg(View view) {
    sendMessage(msgText.getText().toString().trim());
    msgText.setText("");
    refreshData();
}

//send msg to firebase database
private void sendMessage(String message){

    Message m=new Message();
    m.setMsg(message);
    databaseReference.push().setValue(m);
}

//retrieve msg from firebase database
private void refreshData(){

    databaseReference.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            getUpdates(dataSnapshot);
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            getUpdates(dataSnapshot);
        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

}

private void getUpdates(DataSnapshot dataSnapshot){
    msgs.clear();

    for (DataSnapshot ds:dataSnapshot.getChildren()){
        Message m=new Message();
        m.setMsg(ds.getValue(Message.class).getMsg());
        msgs.add(m);
    }

    if (msgs.size()>0){
        adapter=new MyAdapter(Cont_Admin.this,msgs);
        rv.setAdapter(adapter);
    }else {
        Toast.makeText(Cont_Admin.this,"No data",Toast.LENGTH_SHORT).show();
    }
}

}

Answer 1

 for (DataSnapshot ds:dataSnapshot.getChildren()){
    Message m=new Message();
    m.setMsg(ds.getValue(Message.class).getMsg());
    msgs.add(m);
}

这部分是有问题的dataSnapshot已经是'admin_messages'的子节点，因此它是由push()方法推送的节点。 dataSnapshot只有child，它是一个键为msg的字符串，因此;循环子女是不必要的所以，删除并保持它像：

Message m = dataSnapshot.getValue(Message.class);
msgs.add(m);

DatabaseException：无法将java.lang.String类型的对象转换为com.mscit_lab_16.school_management.Message类型

1 个答案: