How to fill a Spinner from my code in Java (Android Studio)

Question

I'm making an example with Android Studio and I want to add items to a List that is displayed in a Spinner. Looking here, I found this answer that helped me a lot.

Basically I create an ArrayAdapter and assign it to my Spinner with the modified list every time I press a button. I was wondering if there is a more efficient way of doing this.

I have an EditText where I write a string and when I press the button I add it to an ArrayList and use it to fill the Spinner.

This is the code of my MainActivity (btnAgregar_Click is the method executed when you press the button):

public class MainActivity extends AppCompatActivity {

    private final List<String> lista = new ArrayList<>();

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

    public void btnAgregar_Click(View v) {
        // Create Java objects that refer to XML interface
        EditText txtArticulo = findViewById(R.id.txtArticulo);
        Spinner spinLista = findViewById(R.id.spinLista);

        // Read text in txtArticulo
        String articulo = txtArticulo.getText().toString();

        // If there is text, add it to the list
        if (articulo.length() > 0) {
            lista.add(articulo);
            txtArticulo.setText("");
        } else {
            // Otherwise, show an error
            Toast.makeText(this,"Error: escribe un artículo",Toast.LENGTH_SHORT).show();
        }

        // Add adapter to the Spinner
        ArrayAdapter<String> adapter = new ArrayAdapter<>(
                this, android.R.layout.simple_spinner_item, lista);

        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinLista.setAdapter(adapter);
    }
}

Although it works, I think it's an overkill to create an ArrayAdapter, initialize it and add it to the Spinner every single time I press the button. Is this the best way to do it? Can I just create the adapter once and just change something when I add an item to the ArrayList?

score 0 · Accepted Answer · answered Mar 10 '23 at 12:35

You are right about creating new instance of ArrayAdapter every time you want to insert a new item. ArrayAdapter has a method add(@Nullable T object) which can be useful in your case. What it does under the hood - it just add new item to internal array and calls notifyDataSetChanged() to let adapter redraw its contents.

So I would rewrite your code as follows:

ArrayAdapter<String> adapter;

public void btnAgregar_Click(View v) {
        // Create Java objects that refer to XML interface
        EditText txtArticulo = findViewById(R.id.txtArticulo);
        Spinner spinLista = findViewById(R.id.spinLista);

        // Read text in txtArticulo
        String articulo = txtArticulo.getText().toString();

        if (!articulo.isEmpty()) {
            if (adapter != null) {
                adapter.add(articulo);
            } else {
                adapter = new ArrayAdapter<>(
                        this, android.R.layout.simple_spinner_item, new ArrayList<String>(){{add(articulo);}});
                adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                spinLista.setAdapter(adapter);
            }
            txtArticulo.setText("");
        } else {
            Toast.makeText(this, "Error: escribe un artículo", Toast.LENGTH_SHORT).show();
        }
    }

As you can see there is no need to manually add item to lista ArrayList. Also it is good practice to let Adapter manage its contents - that is what we do by calling add() method instead of manual modification of lista array. So there will be no hard connections and your code will be more maintainable.

How to fill a Spinner from my code in Java (Android Studio)

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