> For the complete documentation index, see [llms.txt](https://ecm-pmdm-flutter.gitbook.io/1.-introduccion-a-flutter/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ecm-pmdm-flutter.gitbook.io/1.-introduccion-a-flutter/4.-conceptos-fundamentales-en-flutter/widgets/stateless-widget.md).

# Stateless widget

Los widgets **stateless** extienden de la clase **`StatelessWidget`** y son **inmutables** y, por ello, una vez creados, ya no van a cambiar sus propiedades durante la ejecución de la aplicación. 

* Todos sus atributos deberían declararse *final* (aunque Dart no obliga)
* Son widgets que se optimizan internamente por el runtime de Flutter
* Deben de utilizarse siempre que el estado del widget no vaya a cambiar, es decir, depende únicamente de sus datos internos (por ejemplo, recibidos en el constructor).

### **Ejemplo 1**

Creamos una aplicación MaterialApp compuesta por un **stateless** **widget:** **HomePage**, donde **count** es un atributo entero declarado como *final* que no cambiará en tiempo de ejecución.

<pre class="language-dart" data-line-numbers><code class="lang-dart"><strong>import 'package:flutter/material.dart';
</strong>
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Homepage(count: 10),
    );
  }
}

class Homepage extends StatelessWidget {
  final int count;

  const Homepage({required this.count});

  @override
  Widget build(BuildContext context) {
    return Text('Count = $count');
  }
}
</code></pre>

<figure><img src="/files/KfN73g76wKlCTUcnYRRl" alt="" width="314"><figcaption></figcaption></figure>

### Ejemplo 2

En este segundo ejemplo vamos a modificar el valor de `count` y comprobar si se visualiza en pantalla el valor actualizado.  &#x20;

* Para ello, **sustituimos** el código de **Homepage** del **Ejemplo 1** por el siguiente código donde se incrementa el valor de `count` al pulsar el botón.

```dart
class Homepage extends StatelessWidget {
  int count;

  Homepage({required this.count});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Example of Stateless widget'),),
      body: ElevatedButton(
        onPressed: () {
          count++;
          print(count);
        },
        child: Text('Try to increment, COUNT= ${count}'),),
    );
  }
}
```

<figure><img src="/files/GxfWSJIsVpaTOuxtWp3V" alt="" width="375"><figcaption></figcaption></figure>

Si lo **ejecutamos**, comprobaremos que pulsando el botón se imprime en la consola el valor real de `count` pero en realidad, como es un **widget** **inmutable,** Flutter ignora cualquier cambio y **no se actualiza su valor en la UI**.  (<mark style="color:blue;">-> necesitaremos un widget Stateful</mark>)


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