# Coming from React Native

> JSX/useState→Component mapping in Java code, with no bridge and no hot-reload.

Source: https://crossfly.dev/docs/migrate/from-react-native — CrossFly documentation. Full docs as one file: https://crossfly.dev/llms-full.txt

# Coming from React Native

In RN you describe the UI in **JSX** and the re-render happens when the state changes. In CrossFly the UI is
**Java code** built once, and you **mutate**. Read [the philosophy](/docs/migrate/overview) first.

## Translation table
| React Native | CrossFly |
|---|---|
| functional component + JSX | subclass of `Window`/`Component` built in `onShow()` (no markup) |
| `useState` / re-render | fields + `repaint()` |
| `props` | **constructor** arguments (no route table) |
| `<View>` / `<Text>` / `<Image>` | `Component` / `Label` / `ImageView` |
| `<FlatList>` | `VirtualListView` |
| `flexbox` (`flex: 1`) | `add(LAY_FILL, c)` + `VerticalLayout`/`HorizontalLayout` |
| `StyleSheet` | `ComponentStyle` / `Skin` (`ingap`/`outgap` = padding/margin) |
| `react-navigation` | stack of `Window` (`show()` / `hide()`) |
| `useEffect` / `Promise` / `async` | `Thread` + `Component.onUI(...)` |
| `AsyncStorage` | **no equivalent** → SQLite or files in `Device.homeFolder` |

## Before / after — list
```jsx
// React Native
function Lista({ itens }) {
   return <FlatList data={itens}
      renderItem={({ item }) => <Text>{item.nome}</Text>} />;
}
```
```java
// CrossFly — props become constructor arguments; UI in Java
public class Lista extends Window {
   private final List<Item> itens;
   public Lista(List<Item> itens) { this.itens = itens; }   // "props"
   @Override public void onShow() throws Exception {
      super.onShow();
      setLayout(new VerticalLayout());
      add(LAY_FILL, new VirtualListView(Relative.ofFont(3f), new DataAdapter() {
         public int getCount() { return itens.size(); }
         public Component createView() { return new Label(""); }
         public void bindView(Component v, int i) { ((Label) v).setText(itens.get(i).nome); }
      }));
   }
}
```

## What changes the most
- **No JS *bridge* and no hot-reload** — it is compiled Java (on the desktop the cycle is fast; see
  [platforms](/docs/platforms)).
- **`props` → constructor:** pass data via `new Tela(dados)` and call `.show()`.
- **`StyleSheet` → `ComponentStyle`:** padding/margin are `ingap`/`outgap`, not flex properties.

## See also
- [Navigate between screens](/docs/ui/navigation/navigate-between-screens) · [Performance and lists](/docs/best-practices/performance-e-listas-grandes)