Philosophy: CrossFly vs. declarative-reactive

Before the per-origin translation tables, the mental contract that applies to all of them.

The only change that matters

Declarative-reactive frameworks (Flutter, Compose, SwiftUI, React Native) describe the UI as a function of state and rebuild it when the state changes. CrossFly is imperative and object-oriented: you create mutable Component objects once (in onShow()), hold references, change properties, and call repaint().

There is no re-executed build(), no setState, no async/await. What it has in common with Flutter/Compose: everything is rendered via GPU (OpenGL/WebGL), with no native widgets — the look is identical across all platforms.

The mapping of the 4 pillars

In your framework	In CrossFly
re-executed `build()`/`body`	built once in `onShow()`; afterwards you mutate objects
`setState`/`@State`/`useState` → rebuild	change field + `repaint()` (+ `setValidLayout(false)` if the size changed)
nested layout widgets	`add(value, comp)` — `LAY_AUTO`(0f) / `LAY_FILL`(-1f) / fraction
`async`/`await`/`Future`	`Thread` + `Component.onUI(...)` (explicit threading)

The counter, the two models

// Declarative-reactive (pseudo): the state changes → the UI rebuilds itself.
// CrossFly: you keep the reference and update it by hand.
public class Contador extends Window {
   private int n = 0;
   private Label display;
   @Override public void onShow() throws Exception {
      super.onShow();
      setLayout(new VerticalLayout());
      add(LAY_AUTO, display = new Label("0"));
      Button mais = new Button("+");
      mais.onAction(c -> { n++; display.setText(String.valueOf(n)); });  // mutates + repaints
      add(LAY_AUTO, mais);
   }
}

Universal pitfalls (apply to every origin)

Hold references to the components you are going to update (fields of the Window) — there is no way to “find them again” through rebuilding.
Padding/margin are not widgets: they are ingap/outgap in the component’s style.
No hot-reload — it is compiled Java (on the desktop the cycle is fast; see platforms).
Text i18n is manual — there is no built-in string catalog (see i18n).
Colors are int ARGB 0xAARRGGBB — there is no Color class (use UIConstants/ColorUtils).

Choose your origin

Flutter · Jetpack Compose · SwiftUI · React Native · TotalCross/SuperWaba