App architecture

CrossFly imposes no architecture and has no DI or reactive binding (see State and data flow). That’s freedom — and responsibility. Below are suggested conventions (compatible, not mandatory) that scale. This is the task-oriented cut of Chapter 32.

Suggested package structure

app/
 ├─ ui/screens/     → uma tela = uma subclasse de Window
 ├─ viewmodel/      → estado + lógica de apresentação por tela
 ├─ data/repository → fachada sobre dev.crossfly.sqlite / rede
 └─ service/        → serviços de app (singletons) + service locator

One screen = one `Window`

public class ClientesScreen extends Window {
   private final ClientesVM vm = new ClientesVM(Services.get(ClienteRepository.class));
   @Override public void onShow() throws Exception {
      super.onShow();               // build the UI here (valid bounds)
      // … links UI ↔ vm …
      vm.observe(this::render);     // re-renders when the state changes
      vm.carregar();
   }
   @Override public void onRemove() { vm.dispose(); super.onRemove(); }  // release resources
}

Lightweight ViewModel (no `setState`)

Since there’s no reactive binding, the ViewModel holds state and exposes an observe(Runnable); the View re-renders manually:

public class ClientesVM {
   private final ClienteRepository repo;
   private Runnable onChange;
   public List<Cliente> clientes = List.of();
   public ClientesVM(ClienteRepository repo) { this.repo = repo; }
   public void observe(Runnable r) { this.onChange = r; }
   public void carregar() {
      new Thread(() -> {
         List<Cliente> dados = repo.listar();
         Component.onUI(() -> { clientes = dados; if (onChange != null) onChange.run(); });
      }).start();
   }
   public void dispose() { onChange = null; }
}

Repository over SQLite

Isolate data access in a facade — the UI never speaks SQL directly:

public class ClienteRepository {
   public List<Cliente> listar() {
      try (SqliteDb db = SqliteDb.open("app.db");
           SqliteCursor c = db.query("SELECT id, nome FROM cliente")) {
         List<Cliente> out = new ArrayList<>();
         while (c.next()) out.add(new Cliente(c.getLong(0), c.getString(1)));
         return out;
      }
   }
}

In place of DI: a simple service locator

The old Registry was removed. Your own Map<Class,Object> resolves it (or constructor injection):

public final class Services {
   private static final Map<Class<?>, Object> reg = new HashMap<>();
   public static <T> void put(Class<T> k, T v) { reg.put(k, v); }
   public static <T> T get(Class<T> k) { return k.cast(reg.get(k)); }
}
// at bootstrap: Services.put(ClienteRepository.class, new ClienteRepository());

Best practices

UI in onShow(), resources released in onRemove().
State in the ViewModel; mutations return to the paint thread via onUI; the View translates state→components.
The Repository hides SQLite/network; the screen knows no SQL.

Common mistakes

Looking for Flutter’s DI/observables — they don’t exist; use a service locator + manual observe(...).
Putting SQL/HTTP directly in the Window (couples and freezes the UI).
Keeping app state in Window fields (gone when you navigate).