Spinner & AutoCompleteTextView

Both Spinner and AutoCompleteTextView help a user pick from a list of values, but they suit different situations. RecipeBox uses one of each: a Spinner to filter recipes by category, and an AutoCompleteTextView to suggest ingredient names while typing.

Spinner: A Dropdown for a Fixed Set of Choices

A Spinner shows one selected value and, when tapped, opens a dropdown (or dialog) of the other options. RecipeBox's recipe list screen uses one to filter by category:

<Spinner
    android:id="@+id/spCategoryFilter"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

The data can come from a string-array resource in res/values/arrays.xml:

<resources>
    <string-array name="recipe_categories">
        <item>Breakfast</item>
        <item>Lunch</item>
        <item>Dinner</item>
        <item>Dessert</item>
    </string-array>
</resources>

...or from a plain Java List<String> — either way, an ArrayAdapter<String> bridges the data to the Spinner:

Spinner spCategoryFilter = findViewById(R.id.spCategoryFilter);

ArrayAdapter<String> adapter = ArrayAdapter.createFromResource(
        this, R.array.recipe_categories, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spCategoryFilter.setAdapter(adapter);

spCategoryFilter.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        String selectedCategory = (String) spCategoryFilter.getSelectedItem();
        filterRecipesByCategory(selectedCategory);
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) { }
});

Building an ArrayAdapter From a Java List

If the categories come from a database instead of a fixed resource, build the adapter directly from a List<String>:

List<String> categories = recipeRepository.getAllCategoryNames();

ArrayAdapter<String> adapter = new ArrayAdapter<>(
        this, android.R.layout.simple_spinner_item, categories);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spCategoryFilter.setAdapter(adapter);

AutoCompleteTextView: Suggesting Matches While Typing

An AutoCompleteTextView is a regular editable text field that shows a dropdown of matching suggestions as the user types. RecipeBox uses one when adding an ingredient to a recipe, suggesting names from a list of previously used ingredients:

<AutoCompleteTextView
    android:id="@+id/actvIngredient"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Add an ingredient"
    android:completionThreshold="1" />

AutoCompleteTextView actvIngredient = findViewById(R.id.actvIngredient);

String[] knownIngredients = { "Flour", "Sugar", "Eggs", "Butter", "Basil", "Garlic", "Onion" };

ArrayAdapter<String> ingredientAdapter = new ArrayAdapter<>(
        this, android.R.layout.simple_list_item_1, knownIngredients);
actvIngredient.setAdapter(ingredientAdapter);

The Modern Material Alternative: ExposedDropdownMenu

Material Design's newer ExposedDropdownMenu pattern (a TextInputLayout wrapping a non-editable AutoCompleteTextView) gives you Spinner-like fixed-choice behavior but with Material's floating label, outlined box, and dropdown arrow styling. It's worth adopting once you're using Material Components throughout the app; see Material Components (Java) for the full setup.

Which One Should You Reach For?