# The lifecycle > From bootstrap to component — Main, Window.onShow, and the onAdd(firstTime)/onRemove hooks. Source: https://crossfly.dev/docs/concepts/lifecycle — CrossFly documentation. Full docs as one file: https://crossfly.dev/llms-full.txt # The lifecycle The CrossFly lifecycle has three levels: the **application**, the **window** (screen), and the **component**. ## Level 1 — application: the bootstrap (`Main`) `Main` is libGDX's `ApplicationListener`. When the platform comes up, libGDX calls `Main.create()` on the paint thread, and `Main`: 1. detects the platform and initializes the runtime and the device configuration; 2. resolves the name of the **main window** (from a `classname` argument or from `getMainWindow()`); 3. **instantiates that window by reflection** (`Class.forName(...)` → `newInstance()`) and calls its `onShow()`. After that, libGDX calls `render()` (on each rendered frame) and `resize()` — always on the paint thread. ## Level 2 — window: `onShow()` Each screen is a subclass of `Window` that **builds its UI in `onShow()`** (with `super.onShow()`): ```java public class TelaHome extends Window { @Override public void onShow() throws Exception { super.onShow(); setLayout(new VerticalLayout()); add(LAY_AUTO, new Label("Início")); } } ``` **Why `onShow()` and not the constructor?** In the constructor, the **bounds and hierarchy are not yet ready** — `Screen.width/height` and the window size are only valid afterward. Building the UI too early leads to wrong measurements. (The window stack and navigation are in [The window stack](/docs/ui/navigation/the-window-stack).) ## Level 3 — component: `onAdd(firstTime)` / `onRemove()` When a component enters the tree, the framework calls **`onAdd(boolean firstTime)`**; when it leaves, **`onRemove()`**. This is where you initialize and release resources: ```java public class Relogio extends Component { private Timer timer; @Override public void onAdd(boolean firstTime) throws Exception { super.onAdd(firstTime); if (firstTime) timer = iniciarTimer(); // resources that must exist only once } @Override public void onRemove() { if (timer != null) timer.cancel(); // always release on exit super.onRemove(); } } ``` **What does `firstTime` distinguish?** A component can be added, removed, and **re-added**. `firstTime == true` only the first time — use it for setup that should not repeat. `onRemove()` is the cleanup counterpart: cancel timers, listeners, cursors. > General rule: **do not** initialize UI/resources in the constructor. Use `onShow()` (window) and > `onAdd(firstTime)` (component), where bounds and hierarchy are already valid.

## See also - Apply: [Navigate between screens](/docs/ui/navigation/navigate-between-screens) - Next: [State and data flow](/docs/concepts/state-and-data-flow)