How to retrieve data from one single userID Firebase Android

问题

In my firebase database, I have list of users that have different information under them. I would like to retrieve information from a single userId, which I will define in the code and I want to only get information from that user.

My data looks like;

UserTable
{
  "fmXWU324VHdDb8v6h7gvNjRojnu33" : {
    "-KbJtw467nl6p253HZ537" : {
      "Name" : "name1",
      "Email" : "something1@something.com",
      "userid" : "fmXWU324VHdDb8v6h7gvNjRojnu33"
    }
  },
  "pJtC45fW0MMi352UiPWnWdIS7h88" : {
    "-Kb012ls9iMnzEL723o9I" : {
      "Name" : "name2",
      "Email" : "something2@something.com",
      "userid" : "pJtC45fW0MMi352UiPWnWdIS7h88"
    },
    "-Kb0aq0q25FJq38256SrC" : {
      "Name" : "name3",
      "Email" : "something3@something.com",
      "userid" : "pJtC45fW0MMi352UiPWnWdIS7h88"
    },
    "-Kb0atopfK64F6jy124Qi1u" : {
      "Name" : "name3",
      "Email" : "something1@something.com",
      "userid" : "pJtC45fW0MMi352UiPWnWdIS7h88"
  }
} 

and I want to, say for example read and display all data from this user "fmXWU324VHdDb8v6h7gvNjRojnu33". I am not sure how I can do that. I tried this, which seems logical but it doesn't seem to work:

df.child("UserTable").child(user.getUid())).addChildEventListener(new ChildEventListener()

it gives this error:

Can't convert object of type java.lang.String to type com.android.example.UserTable

In addition, I have tried:

df.child("UsersTable").child("userid").child(user.getUid()).ad‌​dChildEventListener(‌​new ChildEventListener() 

I can seem to figure out what I am doing wrong, as what I have tried seems logical and should work. Please can someone help me out.

EDITED:

public ArrayList<data> get(String userID){

      df.child("UsersTable").child(userID).ad‌​dChildEventListener(‌​new ChildEventListener()  {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        fetch(dataSnapshot);
    }

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

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {

    }

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

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

return data;

Update

private void fetchData(DataSnapshot dataSnapshot)
{

    for (DataSnapshot ds : dataSnapshot.getChildren())
    {
        Userdetail userdetail =ds.getValue(Userdetail.class);
        userdetails.add(userdetail );
    }
}

回答1:

First initialize your database like this

mDatabase= FirebaseDatabase.getInstance().getReference().child("your_node_name");

then try setting a ValueEventListener to your Database reference. Inside the onDataChange method you can retrieve your data like this

public void onDataChange(DataSnapshot dataSnapshot) {
    User user= dataSnapshot.getValue(User.class);
}

EDIT:

ValueEventListener postListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        User user= dataSnapshot.getValue(User.class);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
};
mDatabase.addValueEventListener(postListener);

回答2:

  DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
mDatabase.child("UsersTable").child(FirebaseAuth.getInstance().getCurrentUser().getUid()).addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if(dataSnapshot.exists())
        {
            for(DataSnapshot userDetails : dataSnapshot.getChildren()) {
                Log.d("valueName:", userDetails.child("Name").getValue());
                Log.d("valueEmail:", userDetails.child("Email").getValue());
                Log.d("valueuserid:", userDetails.child("userid").getValue());
            }
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

use this will solve your problem.

回答3:

Add value event listener instead of child event listener.

df.child("UsersTable").child(user.getUid()).addValueEventListener(newValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
           if(dataSnapshot!=null){
             fetch(dataSnapshot);
           }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });

来源：https://stackoverflow.com/questions/41851973/how-to-retrieve-data-from-one-single-userid-firebase-android