Question

我需要从数据库Firebase检索数据。但是我有问题，因为当我尝试检索数据时，应用程序将停止。

这是restoredPoint.java的代码

final FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference ref = database.getReference("reloadPoint");

ref.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        ReloadPoint rp = dataSnapshot.getValue(ReloadPoint.class);
        System.out.println(rp);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        System.out.println("The read failed: " + databaseError.getCode());
    }
});

ref.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        ReloadPoint newPost = dataSnapshot.getValue(ReloadPoint.class);
        System.out.println("Email: " + newPost.getmEmail());
        System.out.println("Point: " + newPost.getmPoint());
        System.out.println("User id: " + newPost.getmUserid());
    }

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

    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {

    }

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

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

这是ReloadPoint类的代码。

public class ReloadPoint {

private String mEmail;
private String mPoint;
private String mUserid;

public ReloadPoint(String email, String point, String userid) {
   this.mEmail = email;
   this.mPoint = point;
   this.mUserid = userid;

}

public String getmEmail() {
 return mEmail;
}

public void setmEmail(String mEmail) {
    this.mEmail = mEmail;
}

public String getmPoint() {
  return mPoint;
}

public void setmPoint(String mPoint) {
  this.mPoint = mPoint;
}

public String getmUserid() {
    return mUserid;
}

public void setmUserid(String mUserid) {
   this.mUserid = mUserid;
}
}

这是我要从Firebase检索的东西。 this is the child that I want to retrieve
这是Android系统，如果检索的过程成功，将显示检索到的数据。retrievedPoint.xml
日志猫的结果。Log cat result

请帮助我。

Answer 1

如错误消息所暗示，您的ReloadPoint类需要一个无参数的构造函数，例如：

public ReloadPoint() {

}

Answer 2

请像这样在ReloadPoint类中包含无参数构造函数

public ReloadPoint() {

}

查看此问题users does not define no argument constructor

Answer 3

public class ReloadPoint {

private String mEmail;
private String mPoint;
private String mUserid;

//Ni hang lupa ni. apa la sakinah
//Klau da soklan lagi, hbungi kt insta id: nyrtron
public ReloadPoint(){

}

public ReloadPoint(String email, String point, String userid) {
   this.mEmail = email;
   this.mPoint = point;
   this.mUserid = userid;

}

public String getmEmail() {
 return mEmail;
}

public void setmEmail(String mEmail) {
    this.mEmail = mEmail;
}

public String getmPoint() {
  return mPoint;
}

public void setmPoint(String mPoint) {
  this.mPoint = mPoint;
}

public String getmUserid() {
    return mUserid;
}

public void setmUserid(String mUserid) {
   this.mUserid = mUserid;
}
}

我想我已经找到你的问题了。

DatabaseReference ref = database.getReference().child("reloadPoint").child("Waniyanazahri");

更新的答案：看起来您还没有叫课。

ref.addValueEventListener(new ValueEventListener() {
   @Override
   public void onDataChange(DataSnapshot dataSnapshot) {
      //Add this one
      ReloadPoint rp = new ReloadPoint();
      rp = dataSnapshot.getValue(ReloadPoint.class);
      System.out.println(rp);
    }
   @Override
   public void onCancelled(DatabaseError databaseError) {
   System.out.println("The read failed: " + databaseError.getCode());
   }
});

如何在Firebase中将数据检索到Android Studio

3 个答案: