Retrieve data from firebase database on button click

Question

I'm writing an app that allows users to collaborate on inventory by uploading data to a database hosted by firebase. I can write data to it no problem, however it only wants to let me retrieve data when an event is triggered, such as the data being changed. All I want is to retrieve a string that I've saved to the database and set it as the text value of a TextView element on my page, and I want this to happen when I click a button. How do I do this?

Here's the code for the page where the user writes the data:

addButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            DatabaseReference mDatabase;
            mDatabase = FirebaseDatabase.getInstance().getReference();

            String dbLocationTag = location.getText().toString();
            String itemInfo = "Item Description: " + itemDescription.getText().toString() + "\n" + "Job Number: " + jobNumber.getText().toString();

            mDatabase.setValue(dbLocationTag, itemInfo);

            Context context = getApplicationContext();
            final Intent inventoryHomeScreen = new Intent();
            inventoryHomeScreen.setClass(context, Inventory_Management.class);
            startActivity(inventoryHomeScreen);
        }
    });

Here's where I would like to be able to retrieve the data:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_inventory__view__item);

    final TextView itemInfo = (TextView) findViewById(R.id.itemInfoTextView);

    final Button viewButton = (Button) findViewById(R.id.viewButton);
    assert viewButton != null;
    viewButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            //I would like to set the text of itemInfo to the data I just wrote

        }
    });
}

Answer 1

You need to use addListenerForSingleValueEvent() to retrieve data

DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();
mDatabase.child("<childName>").addListenerForSingleValueEvent(new ValueEventListener(){
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
});

Here in child you need to mention your child node name

If you want to get change of whole database, simply remove child so it look like mDatabase.addListenerForSingleValueEvent()

Answer 2

You can use addValueEventListener() to retrieve data when an event is triggered.

In your onClick() method you can write :

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();

// In the database whenever any data is changed then the below code snipped is going to be executed.
mDatabase.child("<dbLocationTag>").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

                // the changed value is going to be stored into the dataSnapshot
                // to retrieve value from dataSnapshot we write

                String value = dataSnapshot.getValue(String.class);
                mValueView.setText(value);

                // NOTE: if you've multiple childs of same node then you can use Map to display all of them : EG: 
                /*Map<String, String> map = dataSnapshot.getValue(Map.class);
                String val1 = map.get("val1");
                String val2 = map.get("val2");
                String val3 = map.get("val3");
                Log.v("TAG", "Value 1 "+val1);
                Log.v("TAG", "Value 2 "+val2);
                Log.v("TAG", "Value 3 "+val3);
*/
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

                mValueView.setText(firebaseError.toString());

            }
        });

Answer 3

addButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        DatabaseReference mRef = mDatabaseReference.getDatabase().getReference("users");
        ValueEventListener valueEventListener = new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot ds : dataSnapshot.getChildren()) {
                    Log.d(TAG, "" + ds.getKey());
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        };
    }
});
mRef.addListenerForSingleValueEvent(valueEventListener);

The above method worked for me. Hope it helps for you, too.