android - database.DatabaseException : Can't convert object of type java. lang.String 类型

Question

我的问题

      08-10 04:23:28.820 21501-21501/my.org.medicare.medicareapp E/AndroidRuntime: FATAL EXCEPTION: main                                              Process: my.org.medicare.medicareapp, PID: 21501                                             com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type my.org.medicare.medicareapp.protest
at com.google.android.gms.internal.zzaln.zzd(Unknown Source)
at com.google.android.gms.internal.zzaln.zzb(Unknown Source)
at com.google.android.gms.internal.zzaln.zza(Unknown Source)
at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
at my.org.medicare.medicareapp.FirebaseHelper.fetchData(FirebaseHelper.java:50)
at my.org.medicare.medicareapp.FirebaseHelper.access$000(FirebaseHelper.java:14)            atmy.org.medicare.medicareapp.FirebaseHelper$1.onChildAdded(FirebaseHelper.java60)at com.google.android.gms.internal.zzahe.zza(Unknown Source)                                      at com.google.android.gms.internal.zzaje.zzcta(Unknown Source)                          at com.google.android.gms.internal.zzajh$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
atcom.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

我的主要 Activity 代码:

 rv = (RecyclerView) findViewById(R.id.rv);
        rv.setLayoutManager(new LinearLayoutManager(this));
        //INITIALIZE FIREBASE DB
        db = FirebaseDatabase.getInstance().getReference().child("Pro");;

        helper = new FirebaseHelper(db);
        //ADAPTER
        adapter = new MyAdapter(this, helper.retrieve());
        rv.setAdapter(adapter);

还有我的 FirebaseHelper:

public class FirebaseHelper {
    DatabaseReference db;
    Boolean saved=null;
    ArrayList<protest> spacecrafts=new ArrayList<>();

    public FirebaseHelper(DatabaseReference db) {
        this.db = db;
    }
    //WRITE IF NOT NULL
    public Boolean save(protest spacecraft)
    {
        if(spacecraft==null)
        {
            saved=false;
        }else
        {
            try
            {
                db.child("Pro").push().setValue(spacecraft);
                saved=true;
            }catch (DatabaseException e)
            {
                e.printStackTrace();
                saved=false;
            }
        }
        return saved;
    }

    //IMPLEMENT FETCH DATA AND FILL ARRAYLIST
    private void fetchData(DataSnapshot dataSnapshot)
    {
        spacecrafts.clear();
        //dataSnapshot.getChildren()
        for (DataSnapshot ds : dataSnapshot.getChildren())
        {
            protest spacecraft=ds.getValue(protest.class);
            spacecrafts.add(spacecraft);
        }
    }

    //READ THEN RETURN ARRAYLIST
    public ArrayList<protest> retrieve() {
        db.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                fetchData(dataSnapshot);
            }
            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                fetchData(dataSnapshot);
            }
            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {
            }
            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) {
            }
            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });
        return spacecrafts;
    }
}

我的观点持有人

public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    TextView nameTxt,propTxt,descTxt;
    ItemClickListener itemClickListener;

    public MyViewHolder(View itemView) {
        super(itemView);
        nameTxt= (TextView) itemView.findViewById(R.id.nameTxt);
        propTxt= (TextView) itemView.findViewById(R.id.propellantTxt);
        descTxt= (TextView) itemView.findViewById(R.id.descTxt);
        itemView.setOnClickListener(this);
    }

    public void setItemClickListener(ItemClickListener itemClickListener)
    {
        this.itemClickListener=itemClickListener;
    }
    @Override
    public void onClick(View view) {
        this.itemClickListener.onItemClick(this.getLayoutPosition());
    }

下面是我的数据结构，我试着读“Pro”

Data Structure

我的抗议结构:

public class protest {
    private String name;
    private String contact;
    private String centre;

    public protest(){};

    public String getName(){return name;}
    public String getContact(){return contact;}
    public String getCentre(){return centre;}
    public void setName(String name) {
        this.name = name;
    }
    public void setContact(String contact) {
        this.contact = contact;
    }
    public void setCentre(String centre) {
        this.centre = centre;
    }
}

我可以知道这是什么问题吗？我是 firebase 的新手，我需要你的帮助。我在这里读了一些类似的问题，但我仍然无法解决我的问题。这里有专家可以帮助我吗？

更新:再次测试打印..当 Datasnapshot 转到

  public ArrayList<protest> retrieve() {
        db.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                System.out.println(dataSnapshot.getValue());
                fetchData(dataSnapshot);
            }

08-10 06:26:47.548 26700-26700/my.org.medicare.medicareapp I/System.out: {name=lee, contact=123456, centre=jalan ipoh}

但是当Datasnapshot转到

 private void fetchData(DataSnapshot dataSnapshot)
    {
        spacecrafts.clear();
        //dataSnapshot.getChildren()
        for (DataSnapshot ds : dataSnapshot.getChildren())
        {
            System.out.println(ds.getValue());
            protest spacecraft=ds.getValue(protest.class);
            spacecrafts.add(spacecraft);
        }
    }

08-10 06:26:47.548 26700-26700/my.org.medicare.medicareapp I/System.out: jalan ipoh

问题是什么？

Answer 1

您的 fetchData 函数已经接收 DataSnapshot 作为子节点，但即使在这里您仍然循环遍历子节点，这些子节点将有效地循环各个键(姓名、联系人、中心)。您应该简单地在 DataSnaphot 上调用 getValue 而无需循环:

private void fetchData(DataSnapshot dataSnapshot)
    {
        spacecrafts.clear();        
        protest spacecraft=dataSnapshot.getValue(protest.class);
        spacecrafts.add(spacecraft);        
    }

希望对您有所帮助。