问onclick()中的值直到下次单击时才会显示

EN

DatabaseReference myRef;
private double avgrate;
private String category;

private Button button;
private Spinner categories;
private TextView ratetxt;

protected void onCreate(Bundle savedInstanceState) {
    myRef = FirebaseDatabase.getInstance().getReference("user_account");

    //initialize
    avgrate = 0.0;
    button = (Button) findViewById(R.id.button);
    ratetxt = (TextView) findViewById(R.id.ratetxt);
    ratetxt.setVisibility(View.GONE);

    // for category adapter -- it works
    myRef.child("(username)").child("category").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            final List<String> propertyAddressList = new ArrayList<String>();
            for (DataSnapshot ds : dataSnapshot.getChildren()) {
                String propertyAddress = ds.getKey();
                if (propertyAddress != null) {
                    propertyAddressList.add(propertyAddress);
                    for (DataSnapshot ds2 : dataSnapshot.child(propertyAddress).getChildren()) {
                        String sub = (String) ds2.getValue();
                        if (sub != null && !sub.contains("null")) {
                            propertyAddressList.add(sub);
                        }
                    }
                }
            }
            categories = (Spinner) findViewById(R.id.categ);
            ArrayAdapter<String> addressAdapter = new ArrayAdapter<String>(myactivity.this, android.R.layout.simple_spinner_item, propertyAddressList);
            addressAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            categories.setAdapter(addressAdapter);
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show();
        }
    });

    // ON CLICK
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            category = categories.getSelectedItem().toString();

            if (category.isEmpty()) {
                    Toast.makeText(getApplicationContext(), "ERROR - CHOOSE CATEGORY", Toast.LENGTH_SHORT).show();
                } else {

                    // take average rating -- HERE IS THE PROBLEM

                    myRef.child("(username)").child("rating").child(category).addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            for (DataSnapshot ds : dataSnapshot.getChildren()) {
                                String str = (String) dataSnapshot.child("avg").getValue(String.class);
                                if (str != null) {
                                    avgrate = Double.parseDouble(str);
                                }
                            }
                        }
                        @Override
                        public void onCancelled(DatabaseError databaseError) {
                            Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show();
                        }
                    });

                    ratetxt.setVisibility(View.VISIBLE);
                    ratetxt.setText("AVG. RATE: "+avgrate+"");

    }/*close else*/ }});// End of OnClick()
} // END OF OnCreate()