ListView won't load information on the first instance of Activity

Question

I'm developing an app that allows a user to add properties (as in real houses) to their profile in a realtime database and then display those same houses back in the form of a ListView. Ignore any other property details such as size, price etc. I'm only focusing on putting its name into the listview.

Here is the code:

public class agent_home extends AppCompatActivity {

    private ListView lv;

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

        loadProperties();

        lv = (ListView) findViewById(R.id.lvProperties);

        // ListView Item Click Listener
        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                // ListView Clicked item index
                //int itemPosition = position;

                // ListView Clicked item value
                //String itemValue = (String) lv.getItemAtPosition(position);

                //EditText tvCategory = (EditText) findViewById(R.id.tvCategory);
                //tvCategory.setText(itemValue);

                //InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
                //imm.toggleSoftInput(InputMethodManager.SHOW_FORCED,0);
            }
        });
    }

    public void loadProps(View view) {
        loadProperties();
    }

    private void loadProperties() {
        Toast.makeText(getApplicationContext(),"loadProp run",Toast.LENGTH_SHORT).show();

        List<String> propList = new ArrayList<String>();

        lv = (ListView) findViewById(R.id.lvProperties);

        DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
        DatabaseReference propRef = rootRef.child("Properties");

        propRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists()) {
                    for (DataSnapshot ds : dataSnapshot.getChildren()) {
                        String answer = ds.getKey();
                        DatabaseReference agentRef = propRef.child(answer).child("agent");

                        agentRef.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
                            @Override
                            public void onComplete(@NonNull Task<DataSnapshot> task) {
                                if (!task.isSuccessful()) {
                                    Log.e("firebase", "Error getting data", task.getException());
                                }
                                else {
                                    if (task.getResult().getValue().equals(globals.loggedUser)) {
                                        propList.add(answer);
                                    }
                                    else {
                                        Toast.makeText(getApplicationContext(),"Did not populate list",Toast.LENGTH_SHORT).show();
                                    }
                                }
                            }
                        });
                    }
                }
                else {
                    Toast.makeText(getApplicationContext(),"Doesn't exist",Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) { }
        });

        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, propList);

        lv.setAdapter(arrayAdapter);
    }

    public void addProperty(View view) {
        Intent intent = new Intent(this, add_property.class);
        startActivity(intent);
    }

    public void createCategory(View view) {
        Intent intent = new Intent(this, add_category.class);
        startActivity(intent);
    }

    public void goToLogin(View view) {
        Intent intent = new Intent(this, MainActivity.class);
        startActivity(intent);
    }

    public void goToGoals(View view) {
        Intent intent = new Intent(this, goals.class);
        startActivity(intent);
    }
}

Here is the database structure:

The issue that I'm having as that for some reason the data doesn't load into the listview on the first instance of the Activity. The only way I can get the ListView to show the data is if I logout of the app and login in again after which the ListView shows the correct output. The method and code clearly works as I do get the correct output after the second login, however, I ca't seem to figure out why it wont load the first time. My first instinct is that it was a performance issue as I'm using the Android Virtual Device.

Answer 1

Try to initialize adapter before loading data:

List<String> propList = new ArrayList<String>();
lv = (ListView) findViewById(R.id.lvProperties);
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, propList);

lv.setAdapter(arrayAdapter);

After that, when you load data add it to adapter instead of list:

public void onComplete(@NonNull Task<DataSnapshot> task) {
   if (!task.isSuccessful()) {
      Log.e("firebase", "Error getting data", task.getException());
   } else {
      if (task.getResult().getValue().equals(globals.loggedUser)) {
         arrayAdapter.add(answer);
   } else {                                        
      Toast.makeText(getApplicationContext(),"Did not populate 
      list",Toast.LENGTH_SHORT).show();
   }
}

ArrayAdapter handles notifying list by himself.

Or you can add data to list, and then call arrayAdapter.notifyDataSetChanged() after every insert/delete